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Bones of the Thoracic Region

The skeleton of the thoracic region forms a bony cage, which protects the lungs, heart, and some upper abdominal organs.

This cage is formed by the following bones and cartilages:

1. Thoracic vertebrae and intervertebral discs.
2. Ribs and costal cartilages.
3. The sternum.

The thoracic cage is narrower at its superior end and broader at its inferior end. The cage is flattened anteroposteriorly.

Posteriorly, it is formed by 12 thoracic vertebrae and intervertebral discs. The sidewalls of this cage are made up of 12 ribs on each side.

The posterior end of each arched rib articulates with the vertebral column.

Manubriosternal Angle

The anterior end of each rib is attached to the costal cartilage. Through these costal cartilages, ribs gain attachment to the sternum.

The sternum is a flat narrow bone situated on the anterior aspect of the thoracic cage.

Sternum

The sternum is a flat, elongated bone measuring about 6 inches in length. It is situated anteriorly in the wall of the thorax.

From above downwards, the sternum consists of three portions, i.e., the manubrium, the body, and the xiphoid process.

The body is the middle and largest portion of the sternum. The junction of the manubrium and the upper end of the body forms the manubriosternal joint (the sternal angle).

The junction of the lower end of the body and the xiphoid process forms the xiphisternal joint.

The upper border of the manubrium is concave. It is known as a suprasternal notch.

Manubriosternal Angle

Lateral to the suprasternal notch are clavicular notches that articulate with the medial ends of the clavicles to form sternoclavicular joints.

Read and Learn More Human Osteology Notes

Inferolateral to the clavicular notch there lies a costal notch where the first costal cartilage articulates with the manubrium to form a sternocostal joint. This joint is classified as synchondrosis (primary cartilaginous joint).

The manubrium and the body of the sternum lie in different planes at the manubriosternal joint, therefore the joint projects forwards. This projecting angle is called as angle of Louis or sternal angle.

General Features Manubrium

• The manubrium is the widest and thickest of the three parts of the sternum.
• It is roughly quadrilateral in shape At the sternal angle, the second costal cartilage articulates with the lower end of the manubrium and the upper end of the body.
• As the sternal angle is projecting and subcutaneous it is an easily palpable landmark. This fact is utilized to count the ribs. The rib counting starts with the 2nd rib adjacent to the sternal angle.
• The lower end of the manubrium lies at the level of the lower border of the T4 vertebra.

Body of the Sternum

The body of the sternum is a long and thin plate of bone. Its lateral borders present costal notches for articulation with 2nd to 7th costal cartilages.

All these joints are synovial. In adults, the body of the sternum is made up of four pieces (sternebrae).

These pieces of bones are joined to each other by primary cartilaginous joints. These joints begin to fuse soon after puberty. In an adult, these fusion sites are seen as three transverse ridges.

Xiphoid Process

The xiphoid process is the smallest, triangular part of the sternum. The upper end of the xiphoid process meets the body of the. sternum to form xiphisternal joint.

The lateral border of the xiphoid process has a demi facet for articulation with the 7th costal cartilage.

The xiphoid process is cartilaginous in young people. It begins to ossify at about the third year of age.

Manubriosternal Angle

It gets completely ossified at about 40 years of age. It fuses with the body of the sternum in old people.

Sternum Particular Features

Attachments of Muscles on the Anterior Surface of the Sternum Note the origin of the sternal head of the sternocleidomastoid and pectoralis major muscles and insertion of rectus abdominis with the help.

Muscles attached on the posterior aspect of the sternum. Note the origin of sternohyoid, sternothyroid, and sternocostalis with the help. Also, note the reflection of the pleura on both the sides of sternum.

Sternum Ossification

The sternum develops by the fusion of the right and left cartilaginous plates in the midline. After the fusion, many centers of ossification appear in the cartilaginous model.

Sternum Clinical importance

Fractures

Sternal fractures may occur due to automobile accidents. The sternum is broken into pieces due to crush injuries against the steering wheel.

Sternotomy

For coronary bypass surgery and surgeries on lung, these organs are exposed by cutting the sternum in the midline. A wide gap is exposed between two split parts of the sternum because of the elasticity of the costal cartilage and the flexibility of the ribs. After surgery two splitted parts of the sternum are joined by wire sutures.

Bone marrow biopsy

As the sternum is superficial (subcutaneous) it is best suited for needle biopsy of bone marrow. The bone marrow sample is obtained from the spongy bone of the sternum with the help of a needle. A bone marrow biopsy is needed to diagnose blood abnormalities and for bone marrow transplantation.

Sternum is helpful in the identification of sex To a certain extent the sex of an individual can be identified with the help of the sternum as the female sternum is short and wide as compared to males, Jit, et al. (1980). The determination of the sex of bones is needed in medico-legal cases.

Manubriosternal Angle

Congenital defects of sternum As the sternum develops by the fusion of two halves of the sternum in the midline, if these two pieces fail to fuse then the heart is exposed on the thoracic wall (ectopia cordis).

In this condition, pericardium also fails to form. Sometimes there may be the presence of a foramen in the body of the sternum. This occurs due to faulty ossification.

Ribs

Ribs are curved, flat bones that form the greater part of the thoracic wall.

They are arranged in twelve pairs. The length of the ribs increases from the first to the seventh rib. Thereafter the length gradually decreases from the eighth to the twelfth rib.

Each rib articulates posteriorly with the corresponding vertebra. The anterior ends of ribs (except the eleventh and twelfth ribs) articulate with the sternum through costal cartilages.

Classification of Ribs

There are three types of ribs:

True Ribs

These ribs are directly attached to the sternum through their costal cartilage. The first seven ribs are true ribs and these ribs are also called vertebrosternal ribs.

False Ribs

These ribs are indirectly connected to the sternum. Their costal cartilages are joined to the costal cartilages of superior ribs. The eighth to the tenth ribs are false ribs and are also called vertebrochondral ribs.

Floating Ribs

The eleventh and twelfth ribs are not connected with the sternum. Their anterior ends are free and covered by rudimentary costal cartilage. They are also known as vertebral ribs or floating ribs.

Ribs may also be classified as typical and atypical ribs. The typical ribs are those, that have the same (common) features. The 3rd to the 9th ribs are typical ribs.

Manubriosternal Angle

The atypical ribs have special features therefore can be differentiated from the rest of the ribs. The atypical ribs are 1st, 2nd, 10th, 11th and 12th ribs.

The Typical Ribs

A typical rib consists of a head, neck, tubercle, angle, and shaft. The head is present at the posterior end and bears one or two articular facets.

The tubercle is a knob-like structure present at the junction of the neck and shaft.

The shaft is long and curved. The convex surface is the external surface while the concave surface is the internal surface, which bears a groove called a subcostal groove.

The upper border of the shaft is rounded while the lower border is sharp. The sternal end bears a concave depression for attachment of costal cartilage.

Ribs Side Determination

• The end of the rib having the head, neck, and tubercle (posterior end) should be kept posteriorly.
• The concave curved surface should be kept medially.
• The sharp border (inferior border) of the shaft should be kept downwards.

Thoracic Cage Bones

Ribs Anatomical Position

• The posterior end should be kept near the midline.
• The posterior end is at a higher level as compared to the anterior end.

Ribs General Features

The Posterior or Vertebral End

It includes the head, neck, and tubercle.

• The head presents two articular facets separated by the crest of the head. The lower facet is large and articulates with the body of the numerically corresponding vertebra.
• The upper small articular facet articulates with the body of the adjacent upper vertebra. The crest of the head is connected to the intervertebral disc by intra-articular ligament.
• The neck is short and has a sharp upper border. It is sometimes called as crest of the neck. The neck has an anterior smooth and a posterior rough surface.
• On the posterior aspect of the rib, just lateral to the neck, there is the presence of an elevation called a tubercle. The tubercle has a medial articular (smooth) and lateral non-articular (rough) part.

The Anterior End

The anterior end of the rib has a cup-shaped depression for articulation with the lateral end of the corresponding costal (smooth) cartilage to form a costochondral joint.

The Shaft

The shaft of a typical rib is thin, flat, and curved. It forms the major part of the rib. It
extends between the tubercle and the anterior end of the rib.

• It has a superior rounded border and a sharp inferior border. It has an outer convex and an inner concave surface The inner surface shows a shallow costal groove just above the inferior border.
• The costal groove is well-defined in the middle part of the shaft.
• A short distance lateral to the tubercle rib bends anteriorly. This is called as posterior angle.
• The rib also shows a twisting, because of which, two ends of the rib cannot touch a horizontal plane simultaneously (when kept on the table.

Ribs Particular Features

Thoracic Cage Bones

Joints about the Typical Rib

• The head of a typical rib articulates with the adjacent vertebral bodies (with the numerically corresponding body and a body above it) and intervertebral disc to form a costovertebral joint.
• The costotransverse joint is formed between the costal facet of the transverse process and the articular part of the tubercle.
• This joint is supported by various costotransverse ligaments, i.e., the lateral costotransverse, superior costotransverse, and costotransverse ligaments.

The Muscles Attached to the Rib

The attachments of external intercostal, The various muscles are also attached on the external surface of the ribs, i.e., pectoralis minor, serratus anterior, latissimus torsi, and back muscles.

The parietal pleura is related to the inner surface of the rib.

Nerves and Vessels Related to the Typical Rib

• The sympathetic trunk descends downwards on the anterior aspect of the heads of the typical ribs.
• The intercostal nerve and vessels lie in the costal groove between the internal intercostals and innermost intercostal muscles.

The Atypical Ribs

The First Rib

The first rib is the shortest, broadest, curved, and flat rib. As compared to the typical ribs its head has only one articular facet for the body of the first thoracic vertebra.

The posterior angle of the rib lies at the tubercle itself. The shaft shows inner and outer borders thus superior and inferior surfaces.

(This is in contrast to the typical ribs, which show superior and inferior borders and outer and inner surfaces.)

The superior surface of the first rib is rough and shows the presence of two grooves. The inferior surface is smooth and there is the absence of a subcostal groove.

First Rib Side Determination

• The head, neck, and tubercle are located posteriorly near the midline.
• The broad anterior end lies anteriorly.
• The concave inner border lies medially.
• The rough superior surface of the shaft (having grooves) should face superiorly.

Thoracic Cage Bones

First Rib Anatomical Position

• Keep the posterior or vertebral end near the midline.
• The anterior end is at the lower level as compared to the posterior end. In this position, the upper surface should face anterosuperiorly.

First Rib General Features

First Rib The Posterior End

• The posterior end consists of the head, neck, and tubercle. The head is rounded, small, and bears only one circular articular facet.
• The neck is rounded and extends upwards and posterolaterally.
• The neck shows superior, posterior, inferior, and anterior surfaces.
• The tubercle is large and prominent. The oval articular facet on the tubercle articulates with the transverse process of a first thoracic vertebra.

The Shaft

• The shaft is flat and shows superior and inferior surfaces and outer and inner borders.
• The superior surface of the first rib shows two shallow but wide grooves separated by a faint ridge. This ridge is continuous medially with the scalene tubercle on the inner border.
• The inferior surface is smooth and related to the parietal (costal) pleura.

Particular Features

Attachments of the Muscles on the First Rib

• The subclavius muscle arises from the superior surface near its anterior end.
• The scalenus anterior is inserted on the scalene tubercle. The scalenus medius is attached behind the groove for the subclavian artery.
• The intercostal muscles arise from its outer border.
• The first digitation of the serratus anterior arises from its outer border

Relations of the Nerves, Vessels and Ligaments

• The costoclavicular ligament is attached on its superior surface near its anterior end The inner border gives attachment to the suprapleural membrane.
• The groove anterior to the scalene tubercle lodges the subclavian vein.
• The groove posterior to the scalene tubercle lodges the subclavian artery and lover trunk of the brachial plexus.
• The anterior surface of the neck is related from the medial to lateral side to the sympathetic trunk, first posterior intercostal vein, superior intercostal artery, and ascending branch ofthe ventral ramus of the first thoracic nerve.

The Second Rib

• The second rib is almost twice the length of the first rib. The shaft has an external surface directed laterally and slightly upwards.
• This surface presents a prominent rough area near the middle of the shaft.
• It has a faint, short costal groove in the posterior part of the internal surface, which is directed downwards and medially.

Thoracic Cage Bones

Second Rib Particular Features

• The prominent rough area on the outer surface, just behind the middle of the shaft, gives origin to the 1st and 2nd digitations of the serratus anterior.
• The outer surface in its posterior part gives insertion to the scalenus posterior muscle.
• The intercostal muscles are attached to its upper and lower borders.

The Tenth Rib

It also presents the head, neck, tubercle, posterior angle, and shaft, like a typical rib.

However, it differs from typical ribs because it presents a single articular facet on its head for articulation with the 10th thoracic vertebral body.

The Eleventh Rib

This rib is short as compared to the tenth rib. It has no neck or tubercle.

Its lateral end is tapering while the vertebral end bears a single articular facet for the body of the eleventh thoracic vertebra.

Thoracic Cage Bones

The Twelfth Rib

• The twelfth rib is shorter than the eleventh.
• It is directed downwards, laterally, and forwards.
• Similar to the eleventh rib it has no neck or tubercle.
• It has no angle and there is also the absence of a subcostal groove.
• It has a single facet on the head for articulation with the body of the 12th thoracic vertebra.
• It has a pointed lateral end, which gives attachment to cartilage.
• This rib presents upper and lower borders and anterior and posterior surfaces.

• The anterior surface is smooth and concave and faces slightly upwards.

Particular Features of the 12th Rib

• The medial part of the upper border gives attachment to the intercostal muscles.
• The lateral part of the upper border gives attachment to the diaphragm.
• The quadratus lumborum muscle with its covering (anterior layer of the thoraco¬ lumbar fascia) is attached to the medial half of the anterior surface.
• The transverse abdominis muscle is attached to the lower lateral part of the anterior surface.

• The lower limit of the parietal (costal) pleura crosses the anterior surface of the rib and quadratus lumborum muscle. Thus costodiaphragmatic recess extends on the anterior aspect of the medial half of the rib.
• The attachments of the muscles on the posterior aspect of the twelfth rib.

Ossification of Rib

A typical rib is ossified from one primary and three secondary centers (one for the head and two for the tubercle). Primary and secondary centers fuse after 20 years of age.

The Costal Cartilages

• The costal cartilages are flattened bars of hyaline cartilage.
• They prolong the ribs anteriorly.
• Each costal cartilage has anterior and posterior surfaces and upper and lower borders.

• The first seven costal cartilages join to the sternum.
• The 8th, 9th, and 10th articulate with the cartilage just superior to them. The 11th and 12th costal cartilages form caps on the anterior end of these ribs.
• The length of the costal cartilage increases from the first to the seventh. The length decreases gradually from the 8th to the 12th.
• The costal cartilage provides elasticity and mobility to the thoracic wall.
• They prevent fractures of the sternum and ribs due to their resilience.

Costal Cartilages Clinical Importance

Fractures of Ribs

• When there occurs a direct injury on the sidewall of the chest, the broken ends of the ribs may tear the pleura and lung. This may lead to the collection of air (pneumothorax) or blood (haemothorax) in the pleural cavity.
• When there is indirect violence, due to compression of the chest against the steering wheel in accidents, ribs are commonly fractured near their angles.
• Ribs are Used for Bone Grafting Similar to the fibula ribs are also used for bone grafting. In this procedure, the periosteum of the rib is incised along its length and a segment of the rib is removed for grafting leaving the periosteum intact. After some time, rib regenerates deep to the periosteum.

Extra Ribs

• Sometimes the number of ribs may increase (than normal 12 pairs) due to the presence of a cervical or lumbar rib. The cervical rib articulates with the 7th cervical vertebra but usually fails to attach to the sternum.
• The anterior end of the cervical rib may attach to the first rib. The cervical rib may compress the lower trunk of the brachial plexus.
• This may lead to pain and numbness in the shoulder and upper limb.
• This rib may also compress the subclavian artery resulting in pain in the upper limb due to poor blood supply to the limb muscles. Lumbar ribs are less common as compared to the cervical ribs.

Thoracic Vertebrae

The thoracic part of the vertebral column is formed by the twelve thoracic vertebrae and intervertebral discs. This part of the column is concave anteriorly.

Thoracic vertebrae are larger and stronger than cervical vertebrae.

Compared to the cervical vertebrae they also have longer and larger transverse processes. The following three special features are helpful in the identification of thoracic vertebrae.

• Presence of costal facets or demi-facets on the bodies for articulation with the heads of the ribs.
• Presence of costal facets on their transverse processes for articulation with the tubercle of the ribs (except for Til and T12 vertebrae).
• The spinous processes of T3 to T9 vertebrae are long and slope downwards.
• The spinous process of Til and T12 are shorter, broader, and directed more posteriorly.
• The 2nd to 9th thoracic vertebrae are typical because they bear common bony features. The 1st, 10th 11th, and 12th thoracic vertebrae are atypical.

 

Typical Thoracic Vertebrae

A typical thoracic vertebra is made up of a body and a neural arch (vertebral arch). Each vertebra has seven processes, i.e., four articular processes, two transverse processes, and one spinous process.

Body

The superior and inferior surfaces of the body of a typical vertebra are heart shaped

The lateral aspect of the body, close to its upper and lower borders, shows the presence of two costal demi-facets. The upper demi-facet is usually larger and is close to the pedicle.

It articulates with the numerically corresponding rib. The lower costal demi-facet is smaller and lies in front of the inferior vertebral notch and articulates with the lower rib.

Vertebral Arch

It consists of pedicles and laminae. Pedicles are short and directed backward. Laminae are short, thick, and flat vertical plates of the bone that join in the midline to form the posterior portion of the vertebral arch.

The superior vertebral notch is shallow and present above the pedicle while the inferior vertebral notch is deep and present below the pedicle. The vertebral foramen is small and circular. It is bounded by body, pedicles, and laminae.

Vertebral Arch Processes

The transverse processes are large, club-shaped, and directed laterally and somewhat backward. On their anterior surface, they bear, an oval costal facet for articulation with the tubercle of the rib (costotransverse articulation).

The costal facets on the upper six transverse processes are concave and directed anterolaterally. While the costal facets in the 7th to 10th transverse processes are flat and directed upwards, forwards, and laterally.

The superior articular facets are directed posterolaterally while the inferior articular facets are directed anteromedially. The spinous processes are long and directed downwards

A typical Thoracic Vertebra

First Thoracic Vertebra

• The following features will help to identify the head of rib J’s first thoracic vertebra:
• The body is like cervical vertebrae, i.e., its anteroposterior diameter is less than its transverse diameter.
• There is the presence of a single circular costal facet on the lateral surface of the body for articulation with the head of the first rib.
• Presence of a small costal demi-facet near its lower border for articulation with the upper demi-facet on the head of the 2nd rib.
• The vertebral foramen is large and triangular (similar to the cervical vertebra).
• The spinous process is long and directed backward

Tenth Thoracic Vertebra

The shape of the body is somewhat like lumbar vertebrae.

Mostly it bears a single circular costal facet for the head of the 10th rib.

It means the head of the 10th rib will not articulate with the body of the 9th thoracic vertebra. Hence the body of the 9th vertebra will have only the upper demi-facet.

The costal facet is present on the anterior aspect of the transverse process for the tubercle of the 10th rib.

Eleventh Thoracic Vertebra

• The body is large and somewhat lumbar type.
• A single circular costal facet on the lateral aspect of the body.
• The transverse process is short and bears no costal facet, as the 11th rib is a floating rib.
• The superior and inferior articular facets are thoracic type. (Sometimes inferior articular facet may be lumbar type).
• The spinous process may be somewhat like a lumbar vertebra.

Twelfth Thoracic Vertebra

• The body is large and lumbar-type (kidney-shaped).
• The single circular costal facet for the head of the 12th rib. The facet is present mid-way between the upper and lower borders and tends to encroach on the lateral aspect of the pedicle.
• Similar to the 11th vertebra there is the absence of costal facet on the transverse process.
• The transverse processes of T12 are short (rudimentary) and present three tubercles, i.e., superior, inferior, and lateral. The lateral tubercle represents the true transverse process.
• The inferior articular facets are lumbar-like, i.e., they are convex and face anterolaterally. The superior articular facets are thoracic type, i.e., flat and directed posterolaterally.
• The spinous process is also like a lumbar vertebra, i.e., short, broad, and directed backward.
• Articulation of a Typical Rib with the Vertebrae (Costovertebral and Costotransverse Joints)
• A typical rib articulates posteriorly with the bodies of two adjacent vertebrae and the transverse process of the lower vertebra. Students should practice this articulation with the help of two typical thoracic vertebrae and a typical rib.

The Costotransverse Joint

The articular part of the tubercle of the rib presents an oval facet. It articulates with the articular facet on the transverse process of the corresponding vertebra.

This can be further understood by looking at the articulation of the 7th rib. The head of the 7th rib articulates with the body of the 6th thoracic vertebra (with the demi-facet near its lower border) and with the body of 7th thoracic vertebra (with the demi-facet near its upper border).

The head is also connected with the intervertebral disc between the 6th and 7th thoracic vertebrae. The tubercle of the 7th rib also articulates with the transverse process of the 7th thoracic vertebra.

Ossification of Thoracic Vertebra

A typical thoracic vertebra ossifies by three primary centers, i.e., one for the body and one for each neural arch. These centers unite with each other between 3 to 5 years of age At puberty, five secondary centers appear, i.e., one for the spine, one for each transverse process, and two ring-like centers at the margin of the upper and lower surface of the body.

Tuberculosis of Thoracic Vertebrae Spongy bone in the body of thoracic vertebrae is the most common site of tubercular infection. Tubercular bacilli reach the spongy bone through blood circulation and settle there due to sluggish blood flow and restricted mobility of thoracic coloumn.

The infection leads to the destruction of spongy bone and the production of “Cold pus”. As the chronic injection of tubercle bacilli does not produce the local signs of heat, pain, and redness, it is called a cold abscess. Due to the destruction of spongy bone body is collapsed resulting in the production of kyphosis.

Scoliosis and Kyphosis

The thoracic coloumn is the most common site where scoliosis and kyphosis are produced (See Further Details). Kyphosis is most commonly seen in old age due to weakness of spongy bones of vertebral bodies (Osteoporosis).

Hemivertebra

Sometimes the body of the vertebra ossifies by two primary centers, one for each lateral half of the body. If one of these centers fails to ossify then only half of the vertebral body is formed. This leads to the lateral bending of the column on one side.

Bones Of The Vertebral Column

The vertebral column is present in the central region of the body. It is the main constituent of the axial skeleton.

The column is also called as spine or backbone. The vertebral column extends from the base of the skull to the tip of the coccyx.

The vertebral column is composed of a series of many irregular bones called vertebrae. There are 33 vertebrae in the column, which are connected by intervertebral joints.

The important intervertebral joint is made up of a fibrocartilagenous intervertebral disc that binds the bodies of two adjacent vertebrae.

The length of the vertebral column is about 70 centimeters in an adult male. About l/4th length of the column is formed by intervertebral discs.

The adult vertebral column is divided into 5 different regions:

The Cervical Region: This part of the column is present in the neck and consists of seven cervical vertebrae.

The Thoracic Region: It is present in the thorax and consists of 12 thoracic vertebrae.

The Lumbar Region: It is present in the abdominal part and is made up of 5 lumbar vertebrae.

The Sacral Region: It is present in the pelvic region and consists of five fused sacral vertebrae. These five fused vertebrae are considered as a single bone, the sacrum.

The Coccygeal Region: It is present at the lower end of the column. It is usually a single bone, which is formed by the fusion of four coccygeal vertebrae.

When you shall view the articulated vertebral column from the front (anterior aspect) you shall notice the progressive increase in the width of the vertebral bodies from above downwards (from C2 to L5). This is because, at each vertebral segment, some more load is added to the column.

Read and Learn More Human Osteology Notes

Curves of the Vertebral Column

When viewed from the lateral side, the vertebral column of an adult shows four curvatures, i.e., cervical, thoracic, lumbar, and sacral.

• The cervical and lumbar curves are convex anteriorly, while the thoracic and sacral curves are concave anteriorly.
• The thoracic and sacral curvatures are called primary curvatures. They are present at the time of birth. These curvatures are formed mainly due to the shapes of vertebrae.
• The cervical and lumbar curvatures are called secondary curvatures because they develop after birth. Cervical curvature develops after the child starts holding the head on the neck. The lumbar curvature develops after an infant assumes an upright posture and begins to walk. Thus secondary curvatures develop due to the posture.
• In adults, cervical and lumbar intervertebral discs are thicker anteriorly thus contributing to anterior convexity. The posterior aspect of the column is formed by laminae, spinous processes, and articular facets.
• The adjacent spinous process and laminae are inter¬ connected with the help of ligaments, while facets form joints.

Functions of the Vertebral Column

• The vertebral column acts as a rigid but flexible column.
• It transmits the weight of the body.
• It supports the head.
• The vertebral column protects the spinal cord and part of the spinal nerves.
• It gives attachments to the ribs and muscles of the back.

Structure And Functions Of A Typical Vertebra

In the following paragraphs, only the generalized description of vertebrae is given.

Vertebral Body The detailed description of cervical vertebrae is given in Chapter 7, thoracic vertebrae in Chapter 5, and lumbar, sacral, and coccyx in Chapter 6.

Though the vertebrae of different regions of the vertebral column vary in size, shape, and other characteristics many basic features are common in these vertebrae.

A vertebra from the mid-thoracic region is best suited to study the basic features of a typical vertebra.

The following description of a typical vertebra is based on the features of a mid-thoracic vertebra.

A typical vertebra consists of:

• A vertebral body.
• A vertebral (neural) arch with seven processes.

Vertebral Body

• Hold a typical thoracic vertebra in your hand and note the following:
• The body of a vertebra is situated anteriorly. It is somewhat cylindrical.
• The cylindrical body is rounded from side to side. Its superior and inferior surfaces are flat.
• Thus the body has six surfaces (anterior, posterior, superior, inferior, and two lateral).
• The anterior, lateral, and posterior surfaces contain minute foramina for the vessels.
• The body is made up of spongy bone and covered by a thin layer of compact bone.
• However, its superior and inferior surfaces are not covered by compact bone but by a thin layer of hyaline cartilage in living persons. The upper and lower surfaces give attachments to the intervertebral discs.

Vertebral Arch

The vertebral arch is situated posterior to the body of the vertebra. It consists of a pair of pedicles and laminae. Seven processes arise from the vertebral arch of a typical vertebra.

Pedicles.

• The pedicles are short, stout bars that are attached to the posterolateral aspects of the body.
• They are attached close to the superior border of the body.
• Pedicles project posteriorly and somewhat laterally from the body to unite with the laminae.
• If we look at the lateral aspect of a vertebra there is the presence of an inferior vertebral notch just below the pedicle.
• This notch is bounded anteriorly by the body superiorly by the pedicle and posteriorly by the inferior articular process.
• The superior vertebral notch is situated above The pedicle. It is much shallower as compared to the inferior vertebral notch.

Laminae

• These are flat vertical plates of the bone that join in the midline to form the posterior portion of the vertebral arch.
• They extend backward and medially from the pedicles.
• Posteriorly, the lamina of the right and left sides fuse in the midline to form a spinous process.
• The body, pedicles, and laminae of a vertebra together enclose a foramen called vertebral foramen.
• Collectively the vertebral foramina of the successive vertebrae form the vertebral canal that transmits the spinal cord.

Transverse Processes

The transverse process extends laterally on each side from the point where the lamina and pedicle join each other.

Articular Processes

There are two superior and two inferior articular processes. They also arise from the junction of pedicle and lamina.

Each particular process bears a smooth articular facet. In the thoracic vertebrae, the superior articular facets face posterolaterally, while the inferior ones face anteromedially.

Spinous Process

It projects posteroinferiorly in the midline from the junction of two laminae

Functions of the Various Components of a Vertebra

• The bodies and intervertebral discs are involved in the transmission of the load of the trunk to the lower limbs.
• The intervertebral discs are shock absorbers and also permit various movements between two successive bodies.
• Articular processes (and facet joints) allow and guide the movements between adjacent vertebrae.
• Facet joints are also involved in the transmission of load. The magnitude of the load transmitted by facet joints varies in various regions of the column, i.e., cervical and lumbar facets are highly loaded while thoracic is least loaded.
• Lamina is also involved in the transmission of load as it passes from superior to inferior articular facet joints.
• In the thoracic region, where the column is concave anteriorly, the load passes from the vertebral arch (lamina) to the body.
• While, in the lumbar region, where the column is concave posteriorly, load passes from the body to the vertebral arch. The transmission of load between the body and the vertebral arch is through the pedicles.
• The spinal cord and its meninges are well protected in the vertebral foramen (canal).
• The transverse and spinous processes give attachment to muscles and act as levers for various movements of the vertebral column.
• Transverse processes in the thoracic region are also involved in the transmission of load from the ribs to the laminae.

Articulation between Two Successive Typical Vertebrae

The articulations between two successive thoracic vertebrae are. Adjacent vertebrae are connected at three intervertebral joints, i.e., one median joint between bodies and two joints between the articular processes of successive vertebrae.

The two adjacent vertebral bodies are joined by the intervertebral disc, which is made up of fibrocartilage. Each disc consists of annulus fibrosus (outer fibrous part) and nucleus pulposus (inner soft part).

The two superior articular processes of a vertebra articulate with the two inferior articular processes of the vertebra situated above it.

Similarly, two inferior articular processes of the vertebra articulate with the two superior articular processes of the vertebra situated below it.

The joints between articular processes are synovial and are also known as facet joints.

The vertebral foramina of the successive vertebrae forms a continuous vertebral canal, that contains the spinal cord and its meninges. The superior and inferior vertebral notches of the adjacent vertebrae join to form the intervertebral foramen through which passes the spinal nerves and vessels.

The boundaries of intervertebral foramen are formed anteriorly by the body of the upper vertebra, the intervertebral disc, and a small part of the body of the lower vertebra.

The upper and lower boundaries are formed by pedicles of the upper and lower vertebrae respectively. The posterior boundary is formed by the lamina of the upper vertebra and facet joint

The articular facets are present on the body and transverse processes of the thoracic vertebra. These are called costal facets.

The costal facets of adjacent bodies articulate with the head of the rib. The facet on the transverse process articulates with the tubercle of the rib.

Principle Distinguishing Features of the Vertebrae of the Various Regions of the Vertebral Column Besides the features mentioned, the following features will help students to distinguish cervical, thoracic, and lumbar vertebrae from one another:

A cervical vertebra can be easily identified because of the presence of a foramen in its transverse process. This foramen is called as foramen transversarium.

A thoracic vertebra is recognized by the presence of articular facets on the body and transverse processes. These facets are called costal facets, which articulate with the ribs.

A lumbar vertebra is recognized because it has a large kidney-shaped body. There is the absence of foramen transversarum in the transverse processes. There is also the absence of costal facets on the body and transverse processes.

The sacrum is easily identified because of its shape. As it is formed by the fusion of five sacral vertebrae, it is a single, curved, and triangular bone.

The coccyx is formed by the fusion of four coccygeal vertebrae. Coccyx is identified by its small size and fused nature.

 

Movements Occurring in the Vertebral Column

As the sacral and coccygeal vertebrae are fused, no movements are possible between these vertebrae.

The cervical, thoracic, and lumbar vertebrae are not fused hence, are mobile.

Two adjacent vertebrae are joined with each other at three intervertebral joints, i.e., by intervertebral disc (between two adjacent bodies) and by two synovial joints (between articular. processes).

The movements between two adjacent vertebrae are slight. But when movements between series of vertebrae are added, the column shows considerable flexibility.

The following movements are possible in the vertebral column:

• Flexion: Forward bending.
• Extension: Backward bending.
• Lateral flexion: Side bending.
• Rotation: Twisting.

In different regions, i.e., cervical and lumbar regions are more mobile as compared to thoracic. Almost all types of movements are possible in the cervical region.

Rotation movement is the main movement of the thoracic region, but this movement is not possible in the lumbar region.

Particular Features of a Typical Vertebra

There are many ligaments, which connect adjoining vertebrae. With the help of these ligaments and intervertebral joints, a flexible but rigid column is formed.

Attachments of Ligaments

The anterior longitudinal ligament is attached to the anterior surfaces of the bodies of successive vertebrae. It is a continuous ligament, which extends from the base of the skull to the sacrum.

The posterior longitudinal ligament is also continuous and attached to the posterior surface of the bodies of vertebrae.

The transverse processes of the adjacent vertebrae are connected by intertransverse ligaments.

• The Ligamentum flava connects the laminae of adjacent vertebrae.
• Similarly, the spinous processes of adjacent vertebrae are connected by interspinous ligaments.
• In the cervical region, the tips of the spines are connected by the elastic ligament, called as ligamentum nuchae.
• The supraspinous ligaments are attached to the tips of spinous processes of vertebrae between the 7th cervical vertebra to the sacrum.

Attachments of Muscles

• Various muscles are attached to the various aspects of vertebrae in different vertebral regions. The attachments of these muscles are described along with the bones of that region.

Clinical importance

Abnormal Curvatures

Following abnormal curvature may be present in the vertebral column:

Kyphosis

This is due to the abnormal increase in the thoracic curvature (increase in the thoracic concavity anteriorly). It is usually seen in old age due to osteoporosis. The osteoporosis leads to the erosion of the anterior part of one or more vertebrae, leading to an increase in concavity.

Lordosis

This is due to the abnormal increase in lumbar curvature (increase in the lumbar convexity anteriorly). This results due to the weakness of the abdominal muscles.

Lordosis may also occur in obese people and pregnant ladies. This is due to the shift in the line of gravity because of an increase in the weight of abdominal contents.

Scoliosis

It is the most common deformity of the vertebral column and is predominantly observed in girls in the teens. In this condition, there is an abnormal lateral curvature associated with the rotation of the vertebrae.

In most cases, the cause of the scoliosis is not known. Known causes are hemivertebra, maldevelopment of one upper limb, and asymmetry in the length of the lower limbs.

Fractures

The fracture of the vertebral column may occur due to forceful flexion or hyperextension of the column.

The forceful sudden flexion of the column may occur due to a fall from the height of the feet or the head. This leads to the impression of fracture and dislocation of one or more successive vertebrae.

This kind of fracture may be associated with the injury to the spinal cord resulting in loss of sensation and paralysis of muscles below the level of injury.

Spondylolysis

In this condition there occurs the breakage (cleft) in the vertebral arch (at lamina between superior and inferior articular processes) of one or both sides. This condition is common in the lower lumbar region. Spondylolysis may result due to excessive mechanical stress.

It is now considered as the fatigue fracture of the lamina. This condition is different from spondylolisthesis (described below). In spondylolysis, there is no displace¬ ment of the vertebral body and it is often asymptomatic (without pain).

Tuberculosis of the Spine

The vertebral bodies are the common sites for the tubercular infection. This is due to the spongy nature of the vertebral body and rich blood supply. Due to the infection, the spongy bone of the body is destroyed and pus is formed. This leads to the collapse of vertebral bodies as the load of the trunk is brought by the upper vertebrae.

Human Osteology Introduction

The subject of “Human Anatomy” is mainly studied with the help of the dissection of cadavers (dead bodies).

The structure of various parts of the body (i.e., muscles, blood vessels, nerves, joints, and organs) and their interrelationship can be easily seen by the dissection of dead bodies.

All these soft structures are arranged around bones, i.e., muscles and ligaments are attached to bones while, nerves, vessels, and other soft structures are related (or present) close to the bones.

It should also be realized that bones form the skeletal framework of the body and, therefore, give shape to the body.

Hence, for a proper understanding of the gross anatomy of any region, it is essential to learn the structure of bones of that region first, i.e., before starting the dissection of that region.

Students should note that gross anatomy can’t be learned without a sound knowledge of osteology.

What is Osteology?
Osteology is a branch of gross anatomy, which deals with the study of bones.

Parts Of The Skeletal System

The skeletal system consists of bones and cartilage. The cartilage is present at the ends of the bone. The skeletal system consists of two main parts, i.e., axial and appendicular skeleton.

The Axial Skeleton consists of bones lying close to the central axis of the body, e.g., skull, vertebrae, sacrum, coccyx, hyoid bone, sternum, and ribs.

The Appendicular Skeleton It consists of the bones of the upper limb and lower limb including bones forming shoulder and pelvic girdles.

Read and Learn More Human Osteology Notes

How many bones are present in a human skeleton? There are approximately 206 bones present in an adult human. Out of these 80 are present in the axial skeleton and 126 in the appendicular skeleton.

The total number of bones in the human body may exceed 206. This is because some accessory (supernumerary) bones may appear especially in the skull and lower limbs.

Bone Structure

Bone is a dynamic living tissue of the body. It is a constantly changing tissue, i.e., old bone tissues are constantly replaced by new ones.

Bone is composed of cells and intercellular matrix. Bundles of collagen fibers are embedded in the matrix. It is hard because of the deposition of calcium salts in the matrix.

Gross (Macroscopic) Structure of An Adult Living Long Bone.

A typical long bone (bone of limb) consists of a shaft or body and two ends. Both the ends of a bone are knobby (enlarged) and are covered by articular cartilage. The shaft of a long bone lies between two ends.

It is narrow in the middle and expanded towards each end. It encloses a cavity called a marrow cavity, which in an adult is filled with yellow bone marrow.

The entire bone is covered with a fibrous membrane (periosteum) except for the areas covered by articular cartilage.

Blood vessels and nerves enter the bone through numerous foramina present near the ends and at the middle of the shaft. The prominent foramen of the shaft is called as nutrient foramen.

Further details of a living long bone may be studied by observing a longitudinal section of any long bone from the upper or lower limb.

The section reveals two different kinds 0f bones, i.e., compact and spongy.

Compact Bone

The compact bone is a dense bone in which no spaces are visible on naked eye examination. Its texture is like an ivory.

Though the compact bone covers the entire bone it is well developed in the shaft or body. The compact bone of the shaft encloses the marrow cavity filled with bone marrow.

Spongy or Trabecular Bone

It is also known as cancellous bone. Spongy bone is a meshwork of bony spicules (small rods and thin curved plates), which enclose large spaces.

The spongy bone occurs at the ends of a long bone. On the outer surface, the spongy bone is always covered with a thin layer of compact bone. The spaces between spicules are filled with red bone marrow

Parts of a Living Long Bone

From the above description it becomes evident that a living long bone consists of the following parts:

1. Shaft or body (Diaphysis and Metaphyses).
2. Two ends (Epiphyses).
3. Articular cartilage.
4. Periosteum.
5. Endosteum.
6. Medullary cavity.
7. Bone marrow.

1. Shaft or Body

The shaft of a long bone is a long, cylindrical (tubular) structure, made up of compact bone. It is also called diaphysis.

It encloses a tubular space called a marrow cavity. The compact bone of the shaft provides support and bears the weight. It is also capable of resisting the various stresses produced by movements.

The expanded distal ends of the shaft or body, where they meet with the articular ends (epiphyses), are called metaphyses.

2. Two Ends of Proximal and Distal

Two ends (proximal and distal) are expanded and made up of spongy bone covered with a thin layer of compact bone. At the ends, a long bone forms synovial joints and thus comes in contact with other bones. The ends are covered by hyaline cartilage. This particular end of a long bone is also called an epiphysis.

3. Articular Cartilage

As stated earlier the ends of a long bone are covered by a thin layer of hyaline cartilage at the site where bone comes in contact with other bone (forms a joint). The articular cartilage provides a smooth surface thus reducing friction between two bones during movements. It also helps in the absorption of shock during movements.

4. Periosteum

The entire outer surface of the bone (except where it is covered by articular cartilage) is covered with a tough sheath of dense connective tissue. This membrane is attached to the bone tissue by Sharpey’s fibers.

The periosteum consists of an outer layer of collagen fibers and fibroblasts and an inner layer of fibroblasts-like cells called osteoprogenitor cells.

The osteoprogenitor cells have the potential to divide and change to osteoblasts (bone-forming cells).

The periosteum serves the following functions:

1. It forms an outer limit of bone and thus maintains its shape. It also protects the bone.
2. The periosteum contains bone-forming cells, which help the bone to grow in diameter.
3. It is richly supplied with blood vessels thus helping in providing nutrition to bone and assisting in fracture repair.
4. It is also richly supplied with sensory nerves, making it sensitive to pain.
5. Periosteum provides attachment to ligaments, tendons, muscles, intermuscular septa, and articular capsule of a joint

5. Endosteum

The endosteum is a cellular membrane that lines the medullary cavity of the shaft and the medullary spaces of spongy bone at the ends. It is composed of a single layer of flattened osteoprogenitor cells and a very small amount of connective tissue.

6. Medullary or Marrow Cavity

It is a space within the shaft or body of a long bone. The marrow cavity of the shaft is continuous with the spaces of spongy bone at the ends.

7. Bone Marrow

The marrow cavity of a newborn is filled with red bone marrow that is actively involved in the formation of blood. Red bone marrow consists of adipose and hemopoietic (blood-forming) tissues.

However, with the advancing age, the red marrow in the shaft of bone is replaced by yellow marrow (fatty marrow), which is unable to produce blood cells.

In adults, red marrow only remains at the ends of long bones, sternum ribs, skull bones, and vertebrae. At these places, red marrow is actively involved in the production of blood cells throughout life.

Some important facts about the bone

Students should note that the above description is of a living bone (bone present in a living person).

They should realize that the bones, that they handle in the classroom, are dry and I devoid of many structural components of a living bone.

For example, a dry bone is not covered by hyaline cartilage at its epiphyseal ends. Similarly, it is also devoid of periosteum, endosteum, bone marrow, blood vessels, and nerves.

Bone is not only a living tissue but it is also a dynamic tissue. It is continuously engaged in building new bone and breaking down the old bone.

Students should also realize that each living bone is not just a bone tissue but somewhat similar to an organ.

It is evident by the fact that a bone consists of not only bone tissue proper but also many other tissues like fibrous membranes (periosteum and endosteum), cartilage (articular cartilage), bone marrow (adipose and hemopoietic tissues), nerves and blood vessels.

Similar to any other organ of the body, bone is also involved in various functional activities (locomotion, support, and protection of delicate organs, formation of blood, and storage of calcium).

Features on the surface of dry bone (bone markings)

In your osteology classroom, you will handle the dead dried bones to learn their general features. The structures, which are attached to a bone or are in close contact with it, in living conditions, leave marks on the bone surface.

The following kinds of bony features (smooth areas, surface elevations, surface depressions, and foramina) can be observed on the surface of dried bones:

Smooth Areas

The smooth areas on a bone are found at places where it gives attachment to muscle fibers; where it is covered by articular cartilage; and where it lies directly beneath the skin in living conditions.

Facet

It is a flat and smooth area on the bone. In a living state, it is covered with articular cartilage, e.g., articular facets on the surface of carpal and tarsal bones.

Surface Elevations

These are of many types, i.e., crest, line, lip, and ridge are elongated surface elevations. While tubercle, tuberosity, epicondyle, and trochanter are irregular elevations.

These surface elevations are mostly due to the attachment of tendons, ligaments, or aponeurosis. Some surface elevations are sharp like the spine, cornu, or styloid process.

Crest: It is a bony ridge, which may be quite wide, e.g., the iliac crest of the hip bone or narrow, e.g., the external occipital crest.

Line: An elevated line on the surface of the bone, e.g., the sole line of the tibia and superior nuchal line of occipital bone.

Condyle: A bony mass, that may have a somewhat rounded or circular articular area, e.g., condyles of the femur.

Epicondyle: Bony eminence (protuberance) situated on the surface of the condyle, e.g., lateral and medial epicondyle of the femur.

Protuberance: A projection from the surface of the bone, e.g., the external occipital protuberance.

Malleolus: It is a rounded bony process, e.g., the medial malleolus of fiber

Spinous process: A spine-like projection, e.g., the spinous process of a vertebra

Trochanter: It is a large blunt elevation from the surface of the bone, e.g., greater and lesser trochanters of the femur.

Tuberosity: A large rounded elevation, e.g., the ischial tuberosity

Tubercle: A raised elevation, but smaller than trochanter, e.g., adductor tubercle of femur

Surface Depressions and Foramina

Groove or is an elongated depression on the sulcus: the surface of the bone, e.g., the bicipital groove of the humerus.

The groove or sulcus on a dry bone indicates that the bone in living condition was concerning blood vessels or tendon relation to blood Iliac crest iliac fossa vessels or tendon

Notch: It is a deep indentation at the border of a bone, e.g., greater and lesser sciatic notches of the hip bone and suprascapular notch of the scapula.

Fossa: A depression on the surface of the bone, e.g., the iliac fossa of the hip bone and the olecranon fossa of the humerus.

Foramina: Bones show many openings on the surface, i.e., canals and foramina. A canal is a tunnel-like passage with one opening at each end. These are usually for the passage of blood vessels and nerves.

A bone may also show some other surface features, which you must learn with the help of your teachers.

How to study a bone?

Following guidelines will be of help when you are learning any particular bone for the first time.

While you are studying a bone you should have the same bone before you. There is no sense in reading about a bone, from a book, without having that bone in your hand.

The first step in learning a bone is to identify its ends (upper end, lower end, etc.), borders, and surfaces. This can be learned with the help of your teachers or with the help of diagrams from this book.

The second step is to identify some of the important projections (e.g., spine, tubercle, ridge, condyle, etc.) and depressions (e.g., fossa, foramen, notch, etc.), if present on the bone.

Side Determination of the Bone

Once you have identified the ends, borders, and surfaces and some of the bony features you will be able to determine the side of the bone.

Take the help of your teachers to know which are the bony features of that particular bone which will help to determine the side of bone.

(In the case of bones belonging to the axial skeleton there is no need to determine the side as many of them are unpaired, i.e., some bones of the skull, vertebrae, etc.). Side determination of the Lateral bone is very important.

Bone Anatomical Position

The next step is to learn to hold the bone in an anatomical position. Once you have determined the side of the bone hold it in the position it occupies in the body (as in anatomical position).

All the description of the bone in the textbooks is given considering the position of the bone in an upright posture (anatomical position).

If the bone, while studying, is not held in an anatomical position, confusion will arise regarding its borders and surfaces.

Bone General Features

Now learn the bony features (“General Features”) of bone in detail. After understanding the general feature it will become very easy to know the side of the bone and to keep it in the anatomical position.

Bone Particular Features

Once you have understood the general features of a bone it is now time to study the “particular features” (attachments of muscles and ligaments and relations of nerves and vessels).

This can be practiced by marking the area of origin of the muscle with red chalk and insertion of muscle with blue chalk on the surface of the bone. All the sites for attachments of ligaments should be marked with green chalk.

Mark the area of bone, which is with the nerve, by a solid line with yellow chalk. Similarly, the relation of artery and vein on the surface of a bone can be marked with the red and blue lines respectively.

Bone Anatomical Position Ossification

You may also study the ossification of bone if needed. (Ask your teacher whether you are supposed to know the ossification or not?).

Note the age of appearance of primary centers, secondary centers, and the time of fusion of primary with secondary centers.

Also, note which ends of a long bone is a “growing end”. Students are suggested to learn about the “ossification” and “growing end of bone” from a book of “General Anatomy.

Bone Anatomical Position Clinical Importance

Lastly, you should also learn the “applied” or “clinical importance” of the bone, if any.

Bones Of The Lower Limb

The lower limb consists of many regions. The following bones are present in various regions of the lower limb:

Pelvic (Hip) Region

Bones of Pelvic (Hip) Region region form the pelvic girdle. The pelvic girdle consists of two hip bones. These bones are united to each other in the midline anteriorly to form a joint known as the pubic symphysis.

Both the hip bones unite posteriorly with the sacrum at the sacroiliac joint. The pelvic girdle (two hip bones) and sacrum together form a basin-like structure called a bony pelvis.

Thigh Bones

This region consists of a single bone called as femur. The upper end of this bone articulates with a hip bone to form a hip joint. The lower end of the femur articulates with the upper end of the tibia to form the knee joint.

Leg Bones

This region consists of two long bones, i.e., medially placed tibia and laterally placed fibula. These two bones, at their lower end, articulate with talus to form ankle joint.

Foot Bones

The skeleton of the foot consists of many bones, i.e., tarsals, metatarsals, and phalanges. These bones form many joints, i.e., intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal.

Hip Bone

The hip bone is n large, irregular, and flat bone. The middle portion of the bone is constricted and carries a cup-shaped deep cavity on the lateral aspect of the bone. This cavity is known as the acetabulum. The bone is expanded above and below the acetabulum.

Read and Learn More Human Osteology Notes

There is the presence of a large oval or triangular aperture just below and medial to the acetabulum. It is called as obturator foramen.

The bone above the acetabulum is expanded and flat. This portion is called ilium. The bone below the acetabulum consists of two parts, i.e., the anterior and inferior, pubis and posterior and inferior, ischium.

(Though an adult hip bone is a single bone at birth each hip bone consists of three separate primary bones, i.e., ilium, ischium, and pubis.

These three bones are joined to each other by a Y-shaped tri-radiate hyaline cartilage. These three components of hip bones join each other at the acetabulum. However, these three bones begin to fuse at 15 to 17 years of age.

Though in an adult bone, the site of fusion is not visible between three bones, their names are still used as three parts of hip bone). In Fig. 3.4 medial view of the hip bone is shown.

Hip Bone Side Determination

Take the help of your teacher to determine the side of the hip bone

• The expanded flat part called as ilium, should be kept upwards (superiorly).
• The other expanded part (pubis and ischium) with the obturator foramen should be kept downwards (interiorly).
• The acetabulum should face laterally.
• The lower expanded part (below the acetabulum) has two parts, i.e., thin pubis and thick ischium. The pubis should be directed anteriorly and the ischium posteriorly.
• Many students find it difficult to keep the bone in an anatomical position.
• Therefore you should learn the anatomical position of this bone only after you have learned the general features of all three parts (ilium, ischium, and pubis).

Ilium

Ilium is the largest part of the hip bone. It forms the upper fan-shaped expanded part above the acetabulum. The upper 2/5th of the acetabulum is formed by the ilium.

Ilium General Features

The ilium presents:

• Two ends-Upper and lower.
• Three borders-Anterior, posterior, and medial.
• Three surfaces-Gluteal (lateral), iliac fossa, and sacropelvic.

ilium Ends

• Upper end-The upper end is in the form of an expanded border. It is also called an iliac crest. The iliac crest is a thick and curved border, which is convex upwards.
• This extends between two projections, i.e., anterior superior iliac spine and posterior superior iliac spine.
• The iliac crest is subdivided into ventral and dorsal segments.
• The ventral segment is anterior 2/3rd of the iliac crest and presents an outward convexity, while the dorsal segment forms posterior 1/3 of the crest and presents outward concavity.
• The thick ventral segment of the iliac crest shows an outer lip, intermediate area, and inner lip.
• The outer lip presents a prominence about 5 cm behind the anterior superior iliac spine. This is called as tubercle of the iliac crest.
• The dorsal segment of the iliac crest presents medial and lateral sloping surfaces separated by a ridge.

Lower end-The lower end of the ilium lies in the acetabulum and forms the upper 2/5th of this cup-shaped cavity. At the lower end, ilium becomes continuous with the ischium and pubis. The lower end of the ilium meets with the pubis at iliopubic eminence.

Ilium Borders

Anterior border The anterior border of the ilium extends from the anterior superior iliac spine to the acetabulum. The lowest part of this border projects forwards, near the upper margin of the acetabulum, to form the anterior inferior iliac spine.

The posterior border extends from the posterior superior iliac spine to the greater sciatic notch.

Here it becomes continuous with the upper end of the posterior border of the ischium. This border presents a posterior inferior iliac spine and greater sciatic notch.

Medial border The medial border is present on the inner aspect (medial surface) of the ilium. This border extends from the iliac crest to the iliopubic eminence.

It lies between the iliac fossa and the sapropelic surface of the ileum. The medial border is rough in its upper l/3rd, sharp in its middle third, and rounded in the lower l/3rd. The lower one-third of the medial border is called an arcuate line.

Ilium Surfaces

The ilium has an outer gluteal surface and an inner surface, which is further divided into the iliac fossa and sapropelic surface.

The gluteal surface surface is the lateral surface (outer aspect) of the ilium. It has three rough curved lines (the posterior, anterior, and inferior gluteal lines), which divide the gluteal surface into four areas.

Iliac fossa-The iliac fossa is present on the anterior part of the medial surface of the ilium, in front of the medial border. The Iliac fossa presents shallow concavity and has a smooth surface.

The sapropelic surface is also present on the medial surface of the ilium behind the iliac fossa and medial border. It is subdivided into three parts, i.e., iliac tuberosity, auricular surface, and pelvic surface.

The iliac tuberosity is the upper rough part.

The auricular surface is ear-shaped and articular. It is the middle part of the sacropelvic surface, which articulates with the sacrum to form the sacroiliac joint.

The pelvic surface is the smooth surface below and in front of the auricular surface. This surface is continuous with the pelvic surface of the ischium. This surface may present a pre-auricular sulcus in the females who have given birth to children (multiparous).

Pubis

The pubis or pubic bone is situated ventromedial to ilium and ischium. It consists of a body, a superior ramus, and an inferior ramus.

Body of Pubis

The body is flattened and presents three surfaces, i.e., anterior, posterior (pelvic), and medial (symphyseal). The anterior surface faces downwards, forward, and laterally. The posterior surface is smooth and directed upwards and backward.

The symphyseal surface articulates with the corresponding surface of the opposite pubic bone to form a joint known as a pubic symphysis. This surface shows the presence of ridges that change with increasing age (See Further Details).

The superior border of the body of the pubis is thick and known as a pubic crest. At the lateral end of the pubic crest, there is a projection, the pubic tubercle.

Superior Ramus of Pubis

The superior ramus of the pubis arises from the upper and lateral parts of the body of the pubis.

Laterally it extends above the obturator foramen upto the iliopubic eminence where it joins the ilium. Here it also forms the pubic part (anterior 1/5) of the acetabulum. It has three borders (anterior, posterior, and inferior) and three surfaces (pectineal, pelvic, and obturator).

Pubis Borders

• The anterior border is also known as the obturator crest and extends from the pubic tubercle to the acetabular notch.
• The posterior border or pectineal line (pecten pubis) extends from the pubic tubercle to the iliopubic eminence.
• It is a sharp border, which behind the iliopubic eminence becomes continuous with the arcuate line of ilium.
• The inferior border forms the upper border of the obturator foramen.

Pubis Surfaces

• The pectineal surface is situated between the pectineal line and the obturator crest. It is triangular and extends between the pubic tubercle and iliopubic eminence.
• The pelvic surface lies between the pectineal and inferior border of the superior ramus. It is smooth and continuous medially with the pelvic surface of the body of the pubis.
• The obturator surface is situated between the obturator crest and the inferior border. It is a grooved surface and forms the upper boundary of the obturator canal.

Inferior Ramus of Pubis

It extends downwards and laterally from the lower and lateral parts of the body of the pubis. The inferior ramus of the pubis meets the ramus of the ischium to form the conjoined ischiopubic rami. The conjoined ischiopubic rami form the medial boundary of the obturator foramen. It has an anterior and a posterior surface.

Ischium

The ischium forms the posteroinferior part of the hip bone. It consists of a body and a ramus.

Ischium Body

The body lies postero inferior to the acetabulum. It has two ends (upper and lower), three borders (anterior, posterior, and lateral), and three surfaces (femoral, dorsal, and pelvic).

Ischium Ends

• The upper end of the body forms the 2/5 of the posterior and the inferior part of the acetabulum.
• The lower end forms the ischial tuberosity. The ramus of the ischium extends from the lower end of the body upwards, forwards, and medially to meet the inferior ramus of the pubis.

Ischium Borders

• The anterior border forms the posterior margin of the obturator foramen.
• The posterior border is continuous with the posterior border of the ilium. It presents a triangular projection called an ischial spine.
• The ischial spine is placed between the greater sciatic notch (above) and the lesser sciatic notch (below).
• The lateral border extends from the lower margin of the acetabulum and becomes continuous with the lateral margin of the ischial tuberosity.

Ischium Surfaces

• The femoral surface is situated between the anterior and lateral borders.
• The dorsal surface is continuous above the gluteal surface of the ilium. The lower part of the dorsal surface has a large rough area known as ischial tuberosity.

• This tuberosity is divided by a transverse ridge in an upper quadrilateral part and a lower triangular part. Each of these parts (upper and lower) is again divided into medial land lateral parts.
• The pelvic surface of the ischium is smooth and lies between the anterior and posterior borders.

Ramus of Ischium

• It extends from the lower part of the body and runs upwards, forwards, and medially.
• Here it meets the inferior ramus of the pubis and forms the conjoined ischiopubic ramus.
• The conjoined ischiopubic ramus presents upper and lower borders and an outer and inner surface.

Obturator Foramen

It is a large triangular or oval foramen in the lower part of the hip bone. It is situated between the pubis and ischium.

The obturator foramen is bounded above by the superior ramus of the pubis, medially by the body of the pubis and conjoined ischiopubic ramus, and laterally by the body of the ischium.

Acetabulum

• The acetabulum is a deep cup-shaped cavity facing laterally and anterior inferiorly. It is situated on the constricted middle part of the hip bone. All three parts of the hip bone (pubis, ischium, and ilium) contribute to its formation.
• The acetabulum articulates with the head of the femur to form the hip joint.
• The margin of the acetabulum is sharp and deficient in the anteroinferior part. This gap in the margin is called an acetabular notch.
• The floor of the acetabulum has a horseshoe-shaped articular surface (lunate surface) and a non-articular central acetabular fossa.

Anatomical Position of Hip Bone Keeps the bone in such a way that:

• The pubic bone lies anteriorly and the symphyseal surface of the pubis lies in the median plane.
• The acetabulum faces laterally and slightly anteriorly.
• The pubic tubercle and anterior superior iliac spine should lie in the same coronal plane.
• The posterior surface of the body of the pubic bone should face postero-superiorly.
• The ischial spine and superior end of the pubic symphysis are approximately in the same horizontal plane.

Acetabulum Particular Features

Ilium

• The external oblique muscle of the abdomen is inserted on the outer lip into the anterior 2/3rd of a ventral segment of the iliac crest.
• The internal oblique originates from the intermediate area of the ventral segment of the iliac crest.
• The inner lip gives origin to transverse abdominis.
• The tensor-fascia lata muscle arises from the outer lip of the iliac crest near its anterior part.
• Part of the latissimus dorsi arises from the posterior most of the outer lip of the ventral segment.
• The quadratus lumborum arises from the posterior one-third of the inner lip of the ventral segment of the iliac crest.

Attachment of the Muscles on the Dorsal 1/3rd of the Iliac Crest

• The lateral surface of the dorsal segment of the iliac crest gives origin to the gluteus maximus muscle.
• The erector spinae arises from the medial surface of the dorsal segment of the iliac crest.
• Attachment of the Muscles on the Outer Surface (Gluteal Surface) of Ilium.
• The area behind the posterior gluteal line gives origin to the gluteus maximus.
• The area between anterior and inferior posterior gluteal lines gives origin to gluteus medius.
• The area between the anterior and inferior lines gives origin to the gluteus minimus.
• The area below the inferior gluteal line gives origin to the reflected head of the rectus femoris.

Attachment of Muscles on the Inner Aspect (Sacropelvic Surface and Iliac Fossa) of the Ilium

• The iliacus muscle arises from the upper 2/3rd of the iliac fossa.
• The pelvic part of the sapropelic surface of the vilium above the obturator foramen gives origin to the obturator internus muscle.

Muscles Attached to the Anterior Border and Sciatic Notch of the Ilium.

• The anterior superior iliac spine and an area below it give origin to the sartorius muscle.
• The straight head of the rectus femoris arises from the anterior inferior iliac spine.
• A small part of the piriformis arises from the upper border of the greater sciatic notch.

Pubis

Muscles Attached to the Pubic Bone

• The adductor longus muscle arises from a rounded tendon from the anterior surface of the body of the pubis.
• The origin of pyramidal is just above the origin of the adductor longus.
• Note the attachments of gracilis, adductor brevis, and obturator externus on the anterior surface of the body (from medial to lateral).
• These attachments also extend further downwards on the outer surface of the conjoined ischiopubic ramus.
• The obturator internus arises from the pelvic surface of the body and the superior and inferior ramus of the pubic bone.
• The pelvic (posterior) surface of the body gives origin to the anterior fibers of the levator ani.

• The pectineus arises from the pectineal surface of the superior ramus of the pubis.
• Rectus abdominis arises from the pubic crest.

Ischium

Muscles Attached to Ischium

• Note the origin of superior and inferior gemelli concerning lesser sciatic notch.
• The quadratus fetnoris muscle arises from the femoral surface of the ischium.
• The obturator extemus arises from the body and ramus of ischium close to the obturator foramen.
• Posterior fibers of the levator ani and coccygeus muscles arise from the pelvic surface of the ischial spine.
• The origin of muscles from the ischial tuberosity. The adductor magnus arises from the lower lateral part of the ischial tuberosity. The origin also extends on the outer surface of the ramus of ischium.
• The semi-membranosus arises from the upper lateral part of the ischial tuberosity.

• The upper medial part of ischial tuberosity gives origin to the long head of the biceps fetnoris and Semitenditwsus.

Attachment of Ligaments and Fascia on the Hip Bone

• The inguinal ligament is attached medially on the pubic tubercle and laterally on the anterior superior iliac spine.
• The conjoined tendon is attached to the pubic crest and pectin pubis.
• The lacunar ligament is attached to the pubic tubercle and pectin pubis.
• The anterior wall of the rectus sheath is attached to the pubic crest.
• The fascia lata is attached to the outer lip of the iliac crest, pubic crest, and lower border of the conjoined ischiopubic ramus.
• The anterior and middle layer of thoraco lumbar fascia is attached to the iliac crest, anterior and posterior to the attachment of the quadratus lumborum muscle.
• The superior and inferior fascia of the urogenital diaphragm are attached to the conjoined ischiopubic rami.
• The acetabular labrum is attached to the margin of the acetabulum.

• The iliac tuberosity (on the sapropelic surface) gives attachment to the dorsal and interosseous sacroiliac ligament.
• The posterosuperior and posteroinferior iliac spines and posterior border of the ilium give attachment to the upper end of the sacrotuberous ligament.
• The lower end of this ligament is attached to the medial margin of the ischial tuberosity.
• The sacrospinous ligament is attached to the ischial spine.

Blood Vessels and Nerves to the Hip Bone

• The pudendal nerve, nerve to the obturator interims, and internal pudendal vessels lie about the posterior surface of the ischial spine.
• The obturator vessels and nerve lie close to the inferior border of the superior ramus of the pubis (in the obturator canal).
• The superior gluteal vessels and nerves concern the gluteal surface of the ilium.
• The femoral surface of the body of the ischium is with the sciatic nerve and nerve to the quadratus femoris.

Ischium Ossification

The hip bone is organized by three primary centers. Many secondary centers appear at puberty and fuse with the rest of bone between 20 and 25 years of age (two secondary centers for iliac crest, two for acetabular cartilage, one for anterior inferior iliac spine, one for pubic tubercle, and one for pubic crest).

Clinical importance fractures

• Fractures of the hip bone are not very common. They may occur due to roadside accidents or due to sports injuries.
• The direct anteroposterior compression of the hip bone leads to a fracture of the pubic rami. Lateral compression may produce a fracture of the acetabulum.
• Similarly, a fall on the feet from a roof may lead to a fracture of the superior margin of the acetabulum.
• During sports, a sudden pull of muscles attached to anterior superior and inferior iliac spines, ischial tuberosity, and ischiopubic rami may lead to the tearing of these bony projections. These kinds of fractures are called avulsion fractures.
• In this kind of fracture, a small part of the bone with a piece of tendon or ligament attached is torn away.

Femur

• The femur is the bone of the thigh region. It is the longest, strongest, and heaviest bone in the body. The femur consists of a shaft, an upper end, and a lower end.
• The upper end presents a rounded head, which articulates with the acetabulum of the hip bone to form a hip joint. The head is joined to the shaft by an elongated neck.
• The lower end of the femur is expanded and presents two condyles, i.e., medial and lateral, which articulate with tibia and patella to form the knee joint.
• The anterior surface of the shaft is smooth and convex forwards. There is the presence of a rough and thick vertical ridge (lined aspera) on the posterior aspect of the shaft.

Femur Side Determination

• The rounded head is the upper end of the bone.

• The head should be directed upwards, medially, and slightly forward.
• The smooth convex surface of the shaft should be directed forward.

Femur Anatomical Position

The shaft of the femur is obliquely placed (the lower end of the femur is directed downwards and medially).

Because the upper ends of two femora are widely separated by two hip bones two knee joints are placed close to each other when a person stands in the anatomical position.

As the female pelvis is broader the knee joints are more closely placed in females as compared to males.

• Keep the bone in such a way that the head faces upwards, medially, and slightly forwards.
• The long axis of the shaft should be directed downwards and medially so that the two lower surfaces of both the femoral condyles lie in the same horizontal plane.

Femur General Features

The Upper End

The proximal end of the femur consists of a rounded head, neck, and two trochanters (greater and lesser).

Femur Head

The head is like a ball, which forms about 2/3rd of a sphere. Near its middle, there is the presence of a pit for attachment of ligamentum teres.

Femur Neck

The neck connects the head to the shaft. The head and neck make an angle of about 126 degrees with the long axis of the body of the femur. The neck has a superior and an inferior border and an anterior and a posterior surface.

Femur Trochanters

Greater and lesser trochanters are two large elevations at the junction of the neck with the shaft. The greater trochanter is a large, laterally placed quadrilateral mass.

This trochanter presents three surfaces (anterior, medial, and lateral) and a superior and posterior border. The medial surface of the greater trochanter presents a deep depression called as trochanteric fossa. The lateral surface presents an oblique ridge that runs forward and downwards.

The lesser trochanter is a conical projection, directed medially and situated on the posteromedial surface at the neck-shaft The site where the neck joins the shaft, on the anterior aspect, is indicated by the presence of an intertrochanteric line.

This rough line runs between greater and lesser trochanters. On the posterior aspect, a similar but smoother ridge joins two trochanters.

This is known as the intertrochanteric crest, which marks the junction of the neck with the shaft posteriorly. The middle of the intertrochanteric crest presents a quadrate tubercle.

The Shaft

The shaft or body of the femur shows a slight bowing anteriorly. The shaft is narrowest in the middle but expanded towards the upper and lower ends.

• The shaft presents three surfaces (anterior, medial, and lateral) separated by three borders (medial, lateral, and posterior).
• The medial and lateral borders are rounded and featureless.
• The posterior border or linen aspera is a broad, rough vertical ridge.
• As the linea aspera is broad in the middle part of the shaft it presents a medial lip, a lateral lip, and an intermediate area.
• When the linea aspera is traced upwards its lateral lip continues as broad rough gluteal tuberosity and the medial lip continues as a narrow rough spiral line.
• The upper end of gluteal tuberosity extends upto the greater trochanter.
• There lies a small triangular surface (posterior surface) between the gluteal tuberosity and spiral line in the upper third of the shaft.
• When the linea aspera is traced downwards its medial lip continues below as medial supracondylar line.
• Similarly, the lateral lip of linea aspera continues below a lateral supracondylar line. The triangular surface between these two lines is called as popliteal surface.

Lower End

The lower expanded end of the femur consists of medial and lateral condyles, intercondylar fossa, and articular surfaces (tibial and patellar) for articulation with the tibia and patella.
Two condyles are joined together anteriorly but separated posteriorly by the intercondylar fossa or notch.

• Both the condyles of the femur articulate with the corresponding condyles of the tibia and patella to form the knee joint.
• Each condyle presents five surfaces, i.e., anterior, posterior, medial, lateral, and inferior.
• The anterior surfaces of two condyles present an articular patellar surface. It articulates with the posterior surface of the patella.
• The outer surface of both the condyles (medial surface of medial condyle and lateral surface of lateral condyle) is rough and convex.
• The prominent bony points on the outer surfaces of both condyles are called epicondyles.
• An adductor tubercle is present postero-superior to the medial epicondyle at the lower end of the medial supracondylar ridge.
• The inner surface of both the condyles, i.e., the lateral surface of the medial condyle and the medial surface of the lateral condyle form the medial and lateral walls of the intercondylar fossa.
• The inferior and posterior surfaces of both the condyles are articular and articulate with tibia. Anteriorly, the tibial articular surfaces of both condyles are continuous with the patellar surface.

Femur Particular Features

• Muscles Attached to the Upper End of the Femur
• The obturator interims and two Gemelli are inserted on the medial surface of the greater trochanter.
• The obturator externus is attached into the trochanteric fossa.
• The piriformis is inserted on the upper border of the greater trochanter.
• The gluteus minimus is inserted on the anterior surface of the greater trochanter.
• The gluteus medius is inserted on the lateral aspect of the greater trochanter.
• The psoas major is inserted on the lesser trochanter.
• The quadratus femoris is attached to the quadrate tubercle.

Muscles Attached to the Shaft of the Femur

• The iliacus and pectineus are inserted just below the lesser trochanter.
• The insertion of pectineus lies between the gluteal tuberosity and the spiral line.
• A part of the gluteus maximus is inserted on the gluteal tuberosity.
• The vastus medialis has a linear origin, i.e., from the lower part of the intertrochanteric line, spiral line, the medial lip of linea aspera, and upper 2/3rd of the medial supracondylar line.
• Similarly, the origin of vastus lateralis is also linear. It arises from the upper part of the intertrochanteric line, greater trochanter, lateral margin of the gluteal tuberosity, and lateral lip of linea aspera.

• The vast intermediate originates from the anterior and lateral surfaces of the shaft.
• Students should note the attachments of the following structures on the linea aspera, from medial to lateral side, with the help.
• The vastus mediaiis on the medial lip, medial intermuscular septum, adductor brevis (above) adductor longus (below), adductor magnus, posterior intermuscular septum, short head of biceps femoris, lateral intermuscular septum and vastus lateralis.

Muscles attached to the lower end of the femur

• The popliteus muscle takes its origin from the groove present below the lateral epicondyle.
• The medial head of the gastrocnemius arises from the popliteal surface above the medial epicondyle.
• The lateral head of the gastrocnemius arises from the lateral surface of the lateral condyle.
• The lower part of the lateral supracondylar line gives origin to the plantaris.
• The adductor magnus is inserted on the medial supracondylar line.
• The tendon of the ischial part of the adductor magnus is attached to the adductor tubercle.

Attachments of Ligaments and Intermuscular Septa on the Femur A Few important ligaments and septa are described below:

• The pit or fovea on the head of the femur gives attachment to the ligamentum teres.
• The medial intermuscular septum is attached to the medial lip of linea aspera and the lateral septum is attached to the lateral lip.
• The posterior intermuscular septum is attached to the intermediate area of linea aspera.
• The posterior cruciate ligament is attached to the lateral surface of the medial condyle.
• The anterior cruciate ligament is attached to the medial surface of the lateral condyle.

Blood Vessels Concerning the Bone

• The femoral artery lies anterior to the head of the femur.
• The popliteal artery lies on the popliteal surface of the bone.
• Any major nerve is not directly related to the femur.

Femur Ossification

The femur ossifies by one primary and four secondary centers (three for the upper end and one for the lower end. The lower end is the growing end of the femur.

Clinical importance

• The secondary center for the lower end appears just before birth (ninth months of intrauterine life).
• The presence of this center indicates that the fetus is mature (viable) enough to survive after birth.
• The above fact is used as medicolegal evidence in case if a newborn infant found dead was capable of living at birth or not.
• The fracture of the neck of the femur is common in old people, especially in females.
• The fracture through the neck of the femur is also associated with the injury to blood vessels lying on the surface of the neck.
• These vessels are responsible for the blood supply of the head. Rupture of these blood vessels leads to degeneration of the femoral head (avascular necrosis of the head).
• Fracture of the femur between greater and lesser trochanter is also common in old persons.
• Fracture of the shaft is usually a clue to direct injury as in vehicle accidents.
• If the angle of inclination (the angle between the long axis of the body and the long axis of the neck) is reduced then the condition is called coxa vera.
• If this angle is increased the condition is called coxa valga. The normal angle is about 125.

Tibia

• The skeleton of the leg is formed by two long bones, i.e., the tibia and fibula.
• The tibia is the medial weight-bearing bone of the leg. It consists of an upper end and a lover end and a shaft or body. The upper end of the tibia is expanded and bears medial and lateral condyles.
• These condyles articulate with the lower end of the femur to form the knee joint.
• The lower end of the tibia on its medial aspect bears a downward projection called medial malleolus.
• The shaft or the body of the bone bears a prominent sharp ridge known as an anterior border. The upper end of the anterior border bears a projection called tibial tuberosity.

Tibia Side Determination

• The expanded upper end (bearing medial and lateral condyles) should be directed upwards.
• The sharp and prominent anterior border and the tibial tuberosity should be placed anteriorly.
• Medial malleolus at the lower end should face medially.

Tibia Anatomical Position

Bone should be kept vertically by holding it in the same hand, to the side it belongs.

Tibia General Features

Tibia Upper End

• The upper end consists of medial and lateral condyles, an intercondylar area, and a tibial Shaft tuberosity.
• The upper surface of the medial and lateral condyles is articular.
• The articular surface of the medial condyle is oval and large while that of the lateral condyle is small and circular.
• A non-articular rough area is placed between two articular surfaces. This is known as the intercondylar area.
• There is the presence of an elevation in the middle of the intercondylar area (intercondy- lar eminence). This eminence is formed by two tubercles, i.e., medial and lateral intercondylar tubercles.
• The posterior surface of the medial condyle is deeply grooved.
• The posterolateral surface of the lateral condyle bears a circular articular facet for the head of the fibula. This articulation is known as the superior tibio-fibular joint.
• The anterior surface of both condyles bears a triangular area. The apex of this triangle is directed downwards and there lies a rough projection called tibial tuberosity.

• The shaft of the tibia is triangular in cross-section, hence presenting three borders (anterior, medial, and lateral or interosseous) and three surfaces (medial, lateral, and posterior).
• The anterior border extends from the tibial tuberosity to the anterior margin of the medial malleolus. It is a sharp, subcutaneous border.
• The medial border extends from the medial condyle to the posterior border of the medial malleolus.
• The lateral or interosseous border extends from the lateral condyle to the anterior border of the fibular notch at the lower end of the tibia.
• The lateral surface lies between the anterior and interosseous borders.
• The medial surface lies between the anterior and medial borders. This surface is smooth because it is subcutaneous.
• The posterior surface lies between medial and lateral borders. This surface is marked by the presence of an oblique sole line. Thus posterior surface presents a triangular area above the sole line and a medial and a lateral area below the sole line

Tibia Lower End

• This end of the tibia is much less expanded as compared to the upper end. This end projects downwards and medially as the medial malleolus.
• The posterior surface of the malleolus presents a groove. The lateral surface of the lower end shows a triangular area (fibular notch) for articulation with the fibula to form an inferior tibiofibular joint.
• The inferior surface of the lower end including the medial malleolus is articular and articulates with the body of the talus to form the ankle joint.

Tibia Particular Features

Attachment of Muscles on Tibia

• The tibial tuberosity gives attachment to the lignmentum patellae (tendon of quadriceps femoris).
• The semi-membranosus is inserted in the horizontal groove on the posterior surface of the medial condyle.
• The upper part of the media surface receives the insertion of three muscles from before backward, i.e., sartorius, gracilis, and semitendinosus.
• The upper 2/3rd of the lateral surface gives origin to the tibialis anterior.
• On the posterior surface of the bone, the popliteus is inserted above the sole line.

• The sole line itself gives origin to the soleus muscle.
• The medial area below the soleal line, on the posterior surface, gives origin to the flexor digitorum longus. While the lateral area gives origin to the tibialis posterior.

Attachment of Ligaments on the Tibia

• The anterior and posterior parts of the intercondylar area give attachment to the following structures from before backward anterior horn of medial meniscus, anterior cruciate ligament, anterior horn of lateral meniscus, posterior horn of lateral meniscus, posterior horn of medial meniscus, and posterior cruciate ligament.
• The lower end of the iliotibial tract is attached to a small triangular area on the anterior surface of the lateral condyle.

• The tibial collateral ligament is attached to the medial surface near the upper end of the medial border.
• The interosseous or lateral border gives attachment to interosseous membrane.
• The fibular notch gives attachment to the interosseous tibiofibular ligament.

Tendons, Blood Vessels, and Nerves Related to Tibia

Following tendons, vessels, and nerves are related on the anterior aspect of the lower end (from medial to lateral): tibialis anterior, extensor hallucis longus, anterior tibial vessels, deep peroneal nerve, extensor digitorum longus, and peroneus tertius.

Following tendons, vessels, and nerves are related to the posterior aspect of the lower end of the tibia (from medial to lateral side): tibialis posterior, flexor digitorum longus, posterior tibial vessels, posterior tibial nerve, and flexor hallucis longus.

Tibia Ossification

Tibia ossifies from three centers, i.e., one primary center for the shaft and two secondary centers one each for the upper and lower end. The upper end is the growing end of the tibia.

Tibia Clinical importance

• The most common site for the fracture of the tibia is at the junction of the middle and lower 1/3rd.
• This is because the tibia is narrowest at this point. The fracture of the lower 1/3rd of the tibia is difficult to heal as this part of the tibia is devoid of muscle attachment and the periosteal blood supply is poor.
• The tibia is subjected to severe torsion during various sports, which may lead to diagonal fracture of the tibial body. The body of the tibia is also the most common site for compound fracture.
• In a compound fracture, blood vessels and skin are torn by the fractured end of the tibia. This is because the tibia is subcutaneous hence skin is easily torn.

Fibula

The fibula is the lateral bone of the leg. Though the slender fibula has no weight-bearing function, but gives attachment to muscles and its lower end (lateral malleolus) takes part in the formation of the ankle joint.

The fibula has an upper end, a lower end, and an intervening shaft.

The upper rounded end is also known as the head. The head bears a styloid process and an oval articular surface for articulation with the lateral condyle of the tibia.

The lower end of the fibula is expanded anteroposteriorly to form the lateral malleolus.

The medial surface of the lower end presents a triangular articular surface front and a depression, the malleolar fossa, just posteroinferior to the triangular articular surface.

Fibula Side Determination

The side of the fibula can be determined just by looking at its lower end Keep the lower end (lateral malleolus) downwards.

• The triangular articular surface of the lateral malleolus should face medially.
• The malleolar fossa should face downwards, backward, and medially.

Fibula Anatomical Position

Once you have determined the side of the bone then hold the bone vertically in the hand of the same side to which it belongs.

Fibula General Features

Upper End or Head

• It has a pointed apex known as the styloid process.
• The superior surface of the upper end bears an oval articular facet.
• The neck is the constricted part of the bone just below the head.

Lower The End lateral Lateral malleolus

• The malleolus presents lateral, medial, and posterior surfaces and an anterior border.
• The lateral surface is convex, triangular, and continuous above with anterior border. It is a subcutaneous surface.
• The medial surface bears a triangular articular facet for the articulation with the talus.
• Behind the facet there is a rough depression called a malleolar fossa.
• The posterior surface presents a groove for the tendon.

Shaft

The shaft of the fibula has three borders (anterior, interosseous, and posterior) and three surfaces (medial, lateral, and posterior).

(As the borders and surfaces of fibula are difficult to identify, take the help of your teacher. Hold the bone in the anatomical position and trace these borders as described below).

Anterior Border

It begins just below the anterior surface of the head. Trace this sharp border downwards near the lower end of the bone this border splits to enclose a subcutaneous triangular surface on the lateral aspect of the lateral malleolus.

Interosseous Border

• This border is very close and medial to the anterior border.
• It begins just below the anterior surface of the head. When traced downwards it passes medially to end in a rough triangular surface on the medial surface of the lower end.

Posterior Borders

It extends from the posterior aspect of the head to the lateral lip of a groove on the posterior aspect of the lateral malleolus.

Medial (Extensor) Surface It is a very narrow surface and lies between anterior and interosseous borders. It is also known as the anterior surface.

Lateral (Peroneal) Surface It lies between anterior and posterior borders. At the lower end, this surface becomes continuous with the posterior aspect of the lateral malleolus

Posterior (Flexor) Surface

It lies between the interosseous and the posterior border. This surface in its upper 2/3rd is divided into medial and lateral parts by a sharp vertical ridge called as medial crest, of

Attachment of Intermuscular Septum

• The anterior and posterior borders give attachment to the anterior and posterior intermuscular septum.
• The interosseous border gives attachment to the interosseous membrane.
• The medial crest gives attachment to the transverse intermuscular septum.

Attachment of Muscles on Fibula

The medial or extensor surface gives origin to three muscles, i.e., the extensor digitorum.

• longus (from its upper 3/4th surface), extensor hallucis longus (from its middle 2/ 4th), and peroneus tertius from the lower 1 /4th below the origin of extensor digitorum longus.
• The posterior surface gives origin to the tibialis posterior from the anterior concave surface lying anterior to the medial crest.
• The surface posterior to the medial crest gives origin to the soleus in the upper 3/4th and flexor hallucis longus from its lower 3/4th.
• The lateral surface gives origin to the peroneus longus from its upper 3/4th and peroneus brevis from its lower 2/3rd. In the middle third of this surface peroneus brevis lies in front of peroneus longus.
• The lower end of the fibula is devoid of muscular attachments

Tendons and Nerves with Fibula

• The tendon of the peroneus longus and brevis are related to the posterior surface of the lateral malleolus.
• The common peroneal nerve is related to the lateral aspect of the neck of the fibula.

Fibula Ossification

The fibula is organized by three centers. One primary center for the shaft and two secondary centers, one each for the upper and lower ends.

The fibula is an exception to the law of “growing end” (i.e., the secondary center, which appears first is also the first to fuse with the bone formed by the primary center).

Bones Of The Foot

• The bones of the foot consist of tarsus, metatarsus, and phalanges. Each foot consists of 7 tarsal, 5 metatarsal, and 14 phalanges, which are arranged proximodistally.
• Though we shall study the features of individual bones of the foot students are advised to study an articulated skeleton of the foot to see the arrangement of these bones with each other.
• In my opinion, undergraduate students, need not study every bone of the foot in detail. Therefore, only two tarsal bones (calcaneus and talus) are described in detail.

Tarsal Bones

• These are short bones, which form the posterior half of the foot. They are arranged in three rows. The proximal row consists of the talus and calcaneus.
• The calcaneus is the largest tarsal bone and forms the heel of the foot. Placed above the anterior 2/3rd of the calcaneus.

There is another tarsal bone called a talus. The talus articulates with the lower end of the tibia and fibula to form the ankle joint. Anterior to the calcaneus and talus, the middle row is formed by navicular and cuboid bones.

The proximal end of the navicular bone articulates with the head of the talus and is placed medially.

The cuboid bone is placed laterally and articulates proximally with the calcaneus.

The distal surface of the navicular bone articulates with the other three tarsal bones, i.e., medial, intermediate, and lateral cuneiforms.

Talus

The talus has a body, neck, and head. It is situated on the calcaneus.

Body

• The superior surface of the body is articular and bears a large trochlear articular surface for articulation with the lower end of the tibia.
• The medial surface of the body shows a comma-shaped articular facet for articulation with the medial malleolus. While the lateral surface bears a large triangular facet for articulation with the lateral malleolus of the fibula.
• The inferior surface of the body of the talus presents a concave facet, which articulates with the convex facet on the upper surface of the middle third of the calcaneus to form the talar joint.
• The posterior surface is narrow and has a groove for a tendon. This groove has a prominent lateral tubercle and a less prominent medial tubercle.

Neck

The neck of the talus projects forward and medially from the body of the talus. It is nonarticular and bears a groove (sulcus tali) on its inferior surface.

Head

The rounded head is directed forwards, medially, and slightly downwards. The head bears an extensive convex articular surface, which articulates anteriorly with the navicular bone and below with the upper surface of the sustentaculum tali of the calcaneus and spring ligament.

The talus is the only tarsal bone that has no muscular or tendinous attachments. The sulcus tali gives attachment to the interosseous talocalcanean ligament.

Talus Side Determination

• The rounded articular head should be directed forward.
• The large trochlear articular surface should face upward.
• The large triangular articular surface placed on the side of the body should face laterally.

Talus Anatomical Position

Hold the bone in such a way that the head is directed forwards, medially, and slightly downwards.

Calcaneus

The calcaneus is the largest and strongest tarsal bone of the foot. It forms the heel and is located below the talus.

It articulates superiorly with the talus and anteriorly with the cuboid bone. The calcaneus has six surfaces.

The anterior surface is articular and saddle in shape. It articulates with the cuboid bone.

The posterior surface is non-articular and roughing its middle part for the attachment of tendocalcaneus.

The medial surface is concave and bears a shelflike projection called sustentaculum tali.

The lateral surface of the calcaneus is flat and bears a peroneal tubercle.

The plantar or inferior surface of the calcaneus is rough and shows a large prominence on its posterior part called as calcaneal tuberosity.

The calcaneal tuberosity presents medial and lateral tubercles. The anterior part of the plantar surface bears an anterior tubercle.

The dorsal or superior surface is partly articular and partly non-articular. It bears three articular facets (anterior, middle, and posterior facets) for articulation with the corresponding facets on the inferior surface of the talus.

There is the presence of a deep groove between the middle and posterior facets, sulcus calcanei. The sulcus calcanei and sulcus tarsi, in an articulated foot, form sinus tarsi.

Calcaneus Side Determination

• The anterior articular surface should face anteriorly.
• The superior surface bearing three articular facets should face upward.
• The sustentaculum tali projects medially.

Calcaneus Anatomical Position

Hold the bone in such a way that the articular area for the cuboid should face forward and laterally with a slight upward inclination.

Navicular

The navicular bone is boat-shaped. It articulates distally with the head of the talus and proximally with three cuneiforms. The medial surface of the bone bears a navicular tuberosity.

Cuboid

It is the lateral bone extending in the distal row of the tarsus. It is approximately cubical. Proximally it articulates with calcaneus and distally with the 4th and 5th metatarsals.

On the lateral and inferior aspect, it bears a groove for the tendon of the peroneus longus. On this aspect, behind the groove, there is the presence of tuberosity.

The medial surface of the cuboid has articular facets for lateral cuneiform and navicular bone.

Cuneiform Bones

These are called medial, intermediate, and lateral cuneiforms. These bones articulate with the navicular proximally and with the bases of the 1st, 2nd, and 3rd metatarsals distally.

All these bones articulate with each other. The lateral surface of lateral cuneiform also articulates with the cuboid.

The metatarsal bones

• The metatarsals are classified as miniature long bones. The five metatarsal bones are numbered from medial to lateral side, i.e., 1st, 2nd, etc. The first metatarsal is the shortest and strongest as compared to the others.
• The second metatarsal is the longest. Each metatarsal has a proximally placed base, distally placed head, and intervening body. The heads of metatarsals are rounded and articulate with the proximal phalanges.
• The base of each metatarsal is large as compared to its head and presents five surfaces (medial, lateral, dorsal, plantar, and proximal).
• The base of 5th metatarsal has a large tuberosity for the insertion of the tendon of the peroneus brevis.

Phalanges

• Similar to the metatarsals, phalanges are also classified as miniature long bones. The first toe has two phalanges (proximal and distal).
• The lateral four toes have three phalanges each, i.e., proximal, middle, and distal. Each phalanx consists of a proximally placed base, a distally placed head, and an intervening body.
• The first toe consists of two phalanges and has only one interphalangeal joint. While the rest of the toes have proximal and distal interphalangeal joints.

Particular Features Of The Bones Of The Foot

• The peroneus brevis is inserted on the lateral aspect of the base of the fifth metatarsal bone.
• The peroneus tertius is attached to the dorsal aspect of the base of the fifth metatarsal.
• The extens or digitorum longus is attached to the base of the middle and distal phalanges of the lateral four toes.
• The extensor hallucis longus is inserted on the base of the distal phalanx of the great toe.
• The tendocal caneous is inserted in the middle of the posterior surface of the calcaneus.

Attachment of Muscles on the Plantar Aspect of the Bones of Foot

• The flexor hallucis longus is inserted into the base of the distal phalanx of the great toe.
• The flex or digitorum longus is inserted into the plantar surface of the bases of the distal phalanges of lateral four digits.
• The peroneus longus muscle is inserted at the base of the first metatarsal and on the lateral aspect of the medial cuneiform bone.
• The tibialis anterior is inserted into the medial cuneiform and base of the first metatarsal on the medial and plantar aspects.
• The tendon of the tibialis posterior has very extensive insertion. It is mainly inserted into the tuberosity of the navicular bone and medial cuneiform.
• This tendon also sends slips to all other tarsal bones (except the talus) and bases of the 2nd, 3rd, and 4th metatarsals.
• Origin and Insertion of the Intrinsic Muscles of the Foot The dorsal aspect gives origin to the extensor digitorum brevis.

On the plantar surface, many intrinsic muscles are attached (flexor digitorum brevis, abductor digit minim abductor hallucis, flexor digitorum accessories, flexor hallucis brevis, adductor hallucis, and flexor digit minimi brevis).

Students should learn the origin and insertion of all these muscles with the help of The origin and insertion of plantar interossei shown in the dorsal interossei.

Attachment of Ligaments on the Bones of the Foot

• The bones of the foot give attachment to many ligaments. A few important ligaments are described here:
• The interosseous talocalcaneal ligament is attached between the sulcus tali of talus and sulcus calcanei of calcaneus.
• The spring ligament (plantar calcaneonavicular ligament) is attached to the anterior margin of sustentaculum tali of the calcaneus and the plantar surface of the navicular bone.
• On the plantar surface, the long plantar ligament is attached posteriorly to the tuberosity of the calcaneus and anteriorly to the cuboid bone and bases of the 2nd, 3rd, and 4th metatarsal bones.

• The short plantar ligament is proximally attached to the anterior tubercle of the calcaneus and distally on the cuboid.
• The groove on the posterior aspect of the talus is related to the tendon of flexor hallucis longus.

Ossification

Tarsal Bones

Calcaneus is classified by one primary center and one secondary center. All other tarsal bones ossify by one center only. The ossification of metatarsal and phalanges.

Patella

The patella is also known as the kneecap as it lies in front of the knee joint. It is a small triangular bone present in the tendon of the quadriceps femoris.

The patella is not a true bone as it is devoid of periosteum, hence it is classified as a sesamoid bone.

The patella has an apex, a base, medial and lateral borders, and an anterior and a posterior surface. The base forms the upper border of the bone.

The apex is directed downwards. The anterior surface is rough and subcutaneous while the posterior surface is mostly articular.

The articular surface is divided into a smaller medial and a large lateral surface by a vertical ridge. These surfaces articulate with the corresponding surfaces on the femoral condyles.

Patella Side Determination

• The apex of the patella should be directed downwards.
• The smooth articular surface should face posteriorly.
• The larger lateral part of the articular area should lie on the lateral side. The anterior surface is rough (presents several longitudinal ridges). The base, medial, and lateral borders give attachments to many muscles. The posterior surface is mostly articular.

Only a small portion near the apex is rough and gives attachment to the ligamentum patellae. The articular surface is divided into a large lateral and a small medial articular area by a vertical ridge.

These articular surfaces come in contact with the reciprocal patellar articular surface of the femur, i.e., the larger lateral area of the patella with lateral femoral condyle and medial area with medial condyle.

The medial articular area is further separated by a vertical ridge from the most medial narrow strip, which comes in contact with the medial condyle of the femur during full flexion.

As the patella moves downwards when the knee is flexed, its articular areas move on the articular areas at the lower end of the femur.

The various articular areas come in contact with the femur (from extension to full flexion).

Patella Ossification

The patella is cartilaginous up to three years of age. Several ossification centers appear in the patella between 3 to 6 years of age. These centers unite with each other and complete the ossification.