CERVICAL VERTEBRAE

The cervical vertebrae are the smallest of the movable vertebrae. They are identified by the presence of foramina transversia hence they can be easily differentiated from the other vertebrae. There are 7 cervical vertebrae, out of which 3^rd to 6^th (C3, C4, C5 & C6) are typical; while 1^st (C1), 2^nd (C2) and 7^th (C7) are atypical vertebrae. The C1 is located close to the skull and then proceeding away from the skull to spine rest of the vertebrae situated.

The cervical spine supports the weight of the cranium and head & neck motion. The cervical vertebral bodies are relatively smaller than their thoracic and lumbar counterparts due to the relatively lighter load at this spinal level. Consequently, the cervical spine is also more mobile, making it appropriate for supporting head and neck motion like nodding & rotation. However, the increased mobility and flexibility carry a higher spinal cord injury risk in this region. The cervical spine also protects the spinal cord and the foramina transversia allows passage of the blood vessels and sympathetic nerves through it. The cervical portion of the spine is an important one anatomically and clinically. It is within this region that the nerves to the arms arise via the brachial plexus, and where the cervical plexus forms providing innervation to the diaphragm among other structures.

TYPICAL VERTEBRAE

The typical cervical vertebra has a small, cylindrical and somewhat broad vertebral body. It bears less weight than the other vertebrae. The ventral body has the point for intervertebral articulation. The superior surface is concave transversely with upward projecting lips on each side known as the uncinate processes. The ventral body has a convex anterior surface. The anterior and posterior surfaces are flattened and slightly concave, & the discal margin gives attachment to anterior and posterior longitudinal ligament. The inferior surface is saddle shaped, convex from side-to-side & concave from before backwards.

The two pedicles project posterolaterally and longer laminae posteromedially, encloses in a large roughly triangular vertebral foramen. The vertebral foramen is larger than the vertebral body and it accommodates the spinal cord. The pedicles attach to the body midway between the discal surfaces of the body. The two laminae are thin, slightly curved, with thin superior & inferior vertebral notches are of similar depth.

The spinous process is a bony projection which is short, bifid and has 2 tubercles which are unequal in the size. The process extends from the vertebral arch that is from the junction between lamina and pedicle bulges laterally between superior and inferior articular processes to from lateral mass on each side. The nuchal ligament attaches here at the spinous process.

The transverse process is having foramina transversia on each side. The anterior and posterior roots end in the tubercles which is joined by the costotransverse bar or costal lamella. The transverse process gives passage to vertebral arteries, veins and sympathetic nerves. The attachment of anterior root to the pediculolaminar junction and posterior root to the capitellar process. The anterior tubercle of the sixth cervical vertebra is large and is called the carotid tubercle or Chassaignac tubercle because the common carotid artery can be compressed against it.

The superior and inferior articular facets form the articular pillars, it projects laterally at the junction of pedicle and lamina. The facets are flat and ovoid; the superior facet faces backwards, upwards and slightly medially & the inferior facet faces forwards, downwards and slightly laterally. Both the surfaces have a smooth surface known as articular facet. Both the facets articulate with the vertebra above creating the zygapophyseal joints. The intervertebral foramen is a passage way created by the vertebral arch, articular processes and zygapophyseal joints of adjacent vertebra; it allows spinal nerves to exit the vertebral canal from each vertebral level.

Uncinate Processes are bony projections on the lateral sides of the vertebral bodies contribute to the formation of uncovertebral joints, which provide additional stability and limit excessive lateral movement.

ATYPICAL VERTEBRA

The atypical vertebrae are C1, C2 & C7.

1.      FIRST CERVICAL VERTEBRA (ATLAS or C1)

The atlas is the first cervical vertebra which supports the atlanto-occipital joint. It is unique in that it fails to incorporate a centrum, whose expected position is occupied by the dens, a cranial protuberance from the axis. It is in ring shaped, has no body or spine, has short anterior arch, long posterior arch, transverse processes and right & left lateral masses. Due to its ring shape, it helps in accommodating the spinal cord which exits from the foramen magnum. The lateral masses are connected by the anterior and posterior arch.

The anterior arch is convex anteriorly and has a roughened anterior tubercle to which anterior longitudinal ligament is attached. The posterior surface of the anterior arch has a concave, circular facet which articulates with the dens.

The posterior arch forms the 3/5^th of the circumference of the atlantal ring and is larger than the anterior arch. The superior surface bears a wide groove for the vessels and nerves. The posterior surface is marked by the median posterior tubercle.

The lateral masses are oval and bears a kidney shaped superior articular facet to articulate the occipital condyle. The inferior articular facet is circular, flat or slightly concave. On the medial surface of the lateral masses have a roughened area which bears vascular foramina and a tubercle for attachment of transverse ligament.

The transverse processes are longer than all other cervical vertebrae except the 7^th vertebra. These processes act as strong levers for muscles and to keep head balanced. The apex of the transverse process is broad, flat and palpable between mastoid process and ramus of mandible. A small anterior tubercle is sometimes visible on the anterior aspect of the lateral mass. The costal lamella is sometimes deficient, which leaves the foramen transversarium open anteriorly.

2.      SECOND CERVICAL VERTEBRA (Axis or C2)

The axis or the second cervical vertebra which acts as an axle for rotation of the atlas and head around strong dens or odontoid process which projects cranially from the superior surface of the body. The dens is usually believed to represent the centrum or body of the atlas which has fused with the centrum of the axis.

The dens is conical in shape, slightly tilted on the body of the axis. The posterior surface has a broad groove for transverse ligament and is covered in cartilage. The apex is pointed and from there the apical ligament arises. The anterior surface bears an oval articular facet for the anterior arch of the atlas and surface is pitted by many vascular foramina which are numerous near the apex.

The body is a less compact bone which is composite and consists of partly fused centra of the atlas and axis, rudimentary disc between them which usually remains detectable deep within the body of the axis throughout the life. Large ovoid articular facets are present on either side of the dens at the junction of the body and neural arch which are flat or slightly convex for articulation with the masses of the atlas. The facets lie in a plane anterior to the plane of the intercentral (Luschka) articulations, with which they are, in part, homologous.

The pedicles are stout, and the superior surface carries part of the superior articular facet, which also projects laterally and downwards on to the transverse process. The anterolateral surface is deeply grooved by the vertebral artery, running beneath the thin lateral part of the inferior surface of the superior articular facet, which can become quite thin. The inferior surface of each pedicle bears a deep, smooth inferior intervertebral notch, in which the large root sheath of the third cervical nerve lies. The interarticular part of the pedicle is short and lies between the relatively small inferior posterior articular process (which is located at the pediculolaminar junction and bears a small anteriorly facing facet) and the superior articular surface. The transverse process is pointed, projects inferiorly and laterally, and arises from the pediculolaminar junction and the lateral aspect of the interarticular area of the pedicle. The rounded tip is homologous with the posterior tubercle of a typical cervical vertebrae. The foramen transversarium is directed laterally as the vertebral artery turns abruptly laterally under the superior articular facet. Small anterior tubercles may be present near the junction of the costal lamella with the body. The laminae are thick and give attachment to the ligamenta flava. The spinous process is large, with a bifid tip and a broad base, which is concave inferiorly. The ligamentum nuchae is attached to the apical notch.

3.      SEVENTH CERVICAL VERTEBRA (Vertebra Prominens or C7)

The seventh cervical vertebra (C7), also known as the vertebra prominens, is a distinctive and atypical vertebra characterized by its prominent spinous process, which is the longest among the cervical vertebrae and can be easily palpated through the skin at the lower end of the nuchal furrow. This spinous process is thick, nearly horizontal, and non-bifid, ending in a rounded tubercle that provides attachment for the ligamentum nuchae. The transverse processes of C7 are relatively large, with the posterior roots being more prominent than the anterior roots. The transverse foramina are smaller compared to those of other cervical vertebrae and typically transmit vertebral veins but not the vertebral artery. These foramina may be asymmetrical, double, or absent. Anteriorly, the costal lamella is thin, occasionally deficient, and may present as a cervical rib, which can sometimes compress nearby blood vessels or nerves, causing thoracic outlet syndrome. The vertebra's transverse process is grooved superiorly for the seventh cervical nerve and may feature a small anterior tubercle, though the posterior tubercle is more pronounced. While C7 is the most prominent cervical vertebra in about 70% of individuals, it can sometimes be surpassed in prominence by the spinous processes of C6 or T1. These unique anatomical features make C7 distinct among the cervical vertebrae.

MUSCLE & LIGAMENT ATTACHMENTS

The cervical vertebrae, forming the neck region of the spine, exhibit a complex network of muscle and ligament attachments essential for head movement and spinal stability.

Muscle Attachments

• Anterior Tubercle: The superior oblique parts of the longus colli muscle attach to the anterior tubercle on each side.
• Lateral Mass: The anterior surface of the lateral mass provides attachment for the rectus capitis anterior muscle.
• Posterior Tubercle: Just lateral to the posterior tubercle, the rectus capitis posterior minor muscle attaches.
• Transverse Process: The rectus capitis lateralis muscle attaches to the superior surface of the transverse process, while the obliquus capitis superior is located more posteriorly. The obliquus capitis inferior attaches laterally on the apex, below which are slips of the levator scapulae, splenius cervicis, and scalenus medius muscles.
• Body: The anterior surface of the body carries deep depressions on each side for the attachment of the vertical part of the longus colli muscle. The levator scapulae, scalenus medius, and splenius cervicis muscles attach to the tips of the transverse processes, and the intertransverse muscles attach to their upper and lower surfaces.
• Spinous Process: The lateral surfaces of the spinous process give origin to the obliquus capitis inferior muscle, and the rectus capitis posterior major muscle attaches a little more posteriorly. The inferior concavity of the process receives the semispinalis and spinalis cervicis, multifidus more deeply, and the interspinales near the apex.
• Tubercle of the Spinous Process: The trapezius, spinalis capitis, semispinalis thoracis, multifidus, and interspinales muscles all attach to the tubercle of the spinous process.
• Anterior Border of the Transverse Process: The scalenus minimus (pleuralis) muscle, when present, attaches to the anterior border of the transverse process. The first pair of levatores costarum muscles also attaches to the transverse processes.

Ligamentous Attachments

• Anterior Longitudinal Ligament (ALL): Attaches to the anterior and lateral aspects of the vertebral bodies and intervertebral discs, extending from the sacrum to C2.
• Posterior Longitudinal Ligament (PLL): Runs along the posterior aspect of the vertebral bodies or the anterior aspect of the vertebral canal, extending from the sacrum to C2.
• Ligamentum Flavum: Connects the laminae of adjacent vertebrae, limiting hyperflexion and enclosing the posterior aspect of the vertebral canal.
• Intertransverse Ligament: Connects the transverse processes of adjacent vertebrae.
• Interspinous Ligament: Weak ligament connecting the spinous processes of adjacent vertebrae.
• Nuchal Ligament: Continuation of the supraspinous ligament in the cervical spine, resisting hyperflexion.

Unique Ligaments of the Cervical Spine

• Alar Ligament: Connects the dens of C2 to the lateral margins of the foramen magnum.
• Apical Ligament: Connects the tip of the dens of C2 to the anterior aspect of the foramen magnum.
• Transverse Ligament: Holds the dens against the posterior aspect of the anterior arch of C1, forming part of the cruciate ligament.

These intricate muscle and ligament attachments work in concert to provide stability, support, and facilitate a wide range of head and neck movements.

NERVOUS SUPPLY

The cervical spine functions as the spinal cord's bony protection as it exits the cranium. Despite there being only 7 cervical vertebrae, there are 8 pairs of cervical nerves, termed C1 to C8. The first 7 cervical nerves exit the spine cranially to their associated vertebrae, while the 8th cervical nerve exits caudally to C7. 

Direct innervation of the spinal column is highly complex. The sympathetic trunk, sympathetic rami communicantes, and perineural vascular plexus of the vertebral arteries lie in the cervical spine's ventral compartment. Meanwhile, the posterior aspect of the cervical spine receives innervation from the medial branch of the posterior primary rami. Coursing through the intervertebral foramen with the vertebral arteries are the vertebral nerves, which supply additional sympathetic innervation.

BLOOD SUPPLY

The cervical vertebrae are richly vascularized, with blood supply derived from both arterial and venous systems. These blood vessels play essential roles in supporting the metabolic needs of the cervical vertebrae, associated soft tissues, and the spinal cord. Below is a detailed description of the major blood vessels associated with the cervical vertebrae.

Arterial Supply

The arterial supply to the cervical vertebrae is primarily derived from branches of the subclavian arteries, with contributions from the external carotid arteries.

1. Vertebral Arteries

• The vertebral arteries arise as the first branches of the subclavian arteries and ascend through the transverse foramina of the cervical vertebrae, typically from C6 to C1.
• At the atlas (C1), the vertebral arteries curve posteriorly around the superior articular facet before entering the foramen magnum to supply the brain.
• These arteries provide critical branches to the spinal cord, meninges, and cervical vertebrae through:
• Anterior spinal arteries: Supply the anterior portion of the spinal cord.
• Posterior spinal arteries: Supply the posterior aspect of the spinal cord.
• Radicular arteries: Arise as small branches along the spinal cord and help vascularize the spinal nerve roots and nearby vertebrae.

2. Ascending Cervical Arteries

• Branches of the inferior thyroid artery (a branch of the thyrocervical trunk).
• These arteries ascend along the anterior surface of the cervical vertebrae and contribute to the blood supply of the deep cervical musculature, vertebrae, and spinal cord.

3. Deep Cervical Arteries

• Branches of the costocervical trunk (a branch of the subclavian artery).
• These arteries supply the posterior cervical musculature and contribute to the vascularization of the posterior aspects of the cervical vertebrae.

4. Occipital Arteries

• Branches of the external carotid artery, the occipital arteries supply the suboccipital region and upper cervical vertebrae.

5. Small Segmental Branches

• Other small branches from the external carotid artery and thyrocervical trunk provide supplemental blood supply to cervical vertebrae and adjacent soft tissues.

Venous Drainage

The venous system of the cervical vertebrae is interconnected and drains into larger systemic veins. It includes:

1. Vertebral Venous Plexus

• A complex network of interconnected veins located around the vertebral column.
• Composed of two main components:
• Internal vertebral venous plexus: Located within the vertebral canal and drains the spinal cord and meninges.
• External vertebral venous plexus: Located around the outer surface of the vertebrae, draining the vertebral bodies and adjacent muscles.
• The plexuses communicate freely with each other through intervertebral veins that pass through the intervertebral foramina.

2. Vertebral Veins

• These veins accompany the vertebral arteries and ascend through the transverse foramina of the cervical vertebrae.
• They drain blood from the vertebral bodies, cervical spinal cord, and deep neck muscles.
• Vertebral veins eventually empty into the brachiocephalic veins.

3. Deep Cervical Veins

• Run alongside the deep cervical arteries and drain the posterior neck and cervical vertebrae.
• These veins join the vertebral and brachiocephalic veins.

4. Jugular Venous System

Blood from the cervical vertebrae also drains into the internal jugular vein via smaller tributaries, such as those from the occipital veins.

OSSIFICATION

The cervical vertebrae, like other vertebral structures, develop from the paraxial mesoderm, specifically the sclerotome. During the fourth week of embryogenesis, sclerotome cells aggregate around the notochord and neural tube, initiating the formation of the vertebral column. Each vertebra initially forms from three primary ossification centers, one for each half of the neural arch and one for the centrum.

The ossification process in the cervical vertebrae is characterized by several key features:

• Atlas (C1): Ossifies from three primary centers: one for each lateral mass and one for the anterior arch. The lateral mass centers appear around the seventh week of intrauterine life and fuse posteriorly by the age of three. The anterior arch center appears around the first year of life and fuses with the lateral masses by the age of seven.
• Axis (C2): Ossifies from five primary centers: two for the vertebral arch, one for the centrum, and two for the dens. The dens ossifies separately and may not fuse completely with the body of the axis, leading to conditions like os odontoideum.
• Typical Cervical Vertebrae (C3-C7): Ossify from three primary and six secondary centers. The primary centers appear during the ninth to tenth week of fetal life for the neural arches and the third to fourth month for the centrum. The secondary centers, which include epiphyseal discs and tips of transverse processes, appear during puberty and fuse with the rest of the vertebra by the age of 25.

 

PHALANGES OF THE FOOT

The phalanges are the long bones in the foot, distal to the metatarsals. The phalanges of the foot resemble that of the hand, but these are smaller in size & shafts particularly of proximal row are compressed from side to side. They are named as proximal, middle and distal phalanges; there are 2 in the great toe, 3 in all the other toes (but there can be only 2 phalanges in the little toe), hence there are 14 phalanges in total. The phalanges consist pf proximal base, shaft & distal head.

PROXIMAL PHALANGES

The proximal phalanges have a compressed shaft which is convex dorsally (above) & on the plantar side (below) is concave. The base is concave to articulate with the head of the associated metatarsals and forms the metatarsophalangeal joint. The head presents a trochlear surface to articulate the middle phalanx to form the interphalangeal joint.

MIDDLE PHALANGES

The middle phalanges are smaller than the proximal phalanges but, larger than the distal phalanges. The base forms proximal interphalangeal joint with proximal phalanges. The head forms distal interphalangeal joint which is a type of hinge joint forms with distal phalanges. The hinge joint allows flexion & extension movement which are provided by the plantar ligaments & also by medial and lateral collateral ligaments.

DISTAL PHALANGES

The distal phalanges are flat and small. They have a broad base to articulate the middle phalanges. The head is nonarticular & expanded. It has a rough and crescent shaped tuberosity present on the plantar surface of the head to support pads or pulp of the bone which is a weight bearing area.

MUSCLE ATTACHMENTS

The proximal phalanges have attachments of; lumbricals on the medial aspect of the 4 lateral phalanges and interossei on both the sides of 2^nd,3^rd & 4^th phalanges. The plantar interossei attaches on the medial side & on the lateral side there is attachment to abductor digiti minimi & flexor digiti minimi on the little toe. On the great toe there is attachment of abductor hallucis on the medial side and adductor hallucis on the lateral side.

The middle phalanges have attachments of flexor digitorum brevis on both the sides of the shaft at the plantar surface. On the dorsal side of the shaft there is attachment of extensor expansion. The fibrous flexor sheath is attached to the margins of proximal and middle phalanges of lateral 4 toes.

The distal phalanges have attachments of flexor digital longus and extensor digitorum longus on plantar and dorsal aspects respectively on the lateral four toes. Flexor hallucis longus and extensor hallucis longus are attached to plantar and dorsal surface respectively at the great toe.

VASCULAR & NERVOUS SUPPLY

The proximal phalanges get blood supply from the dorsal digital arteries. The middle phalanges are supplied by the dorsal and plantar digital arteries. The distal phalanges get blood supply from plantar digital arteries. All the phalanges are innervated by dorsal and plantar digital nerves.

OSSIFICATION

Ossification is the process of bone formation where cartilage is replaced by bone tissue through the activity of osteoblasts.

Each phalanx begins as a cartilaginous model and develops from a primary ossification center in the shaft. A secondary ossification center forms in the base.

Distal phalanges: Primary ossification centers appear between the 9th and 12th prenatal weeks. The secondary ossification center appears around the sixth year and fuses with the shaft by the eighteenth year.

Proximal phalanges: Primary ossification centers appear between the 11th and 15th prenatal weeks. The secondary ossification center appears around the second year and fuses with the shaft by the eighteenth year.

Middle phalanges: Primary ossification centers appear slightly later than the proximal phalanges. The secondary ossification center appears around the third year and fuses with the shaft by the eighteenth year.

 

METATARSALS

The five metatarsals are a group of long cylindrical bones in the distal half of the foot between tarsals and phalanges. The metatarsal bones lack individual names hence they are numbered from 1 to 5 from medial to lateral side of the foot. The metatarsals are analogous to metacarpals in the hand. The lengths of metatarsals are in descending order 2^nd, 3^rd, 4^th, 5^th and 1^st.

Metatarsals are dorsally convex long bones having a shaft or body, a head and a base, except for 1^st and 5^th metatarsal. The shafts are long and slender, longitudinally convex & from the plantar surface they are concave. The body is prismatic in form which tapers gradually from proximal to distal. The proximal end is set obliquely in such a way which projects backwards and laterally. The base is wedge shaped articulating proximally with the tarsals. The space between two metatarsal bones is known as interosseous metatarsal space. The dorsal or the plantar surface of the is rough for the attachments of ligaments. The head of each metatarsals represent a convex articular surface which articulates the base of proximal phalanx. The medial and lateral surface of the head is flat which has a depression crossed by dorsal tubercle for a collateral ligament of metatarsophalangeal joint.

FIRST METATARSAL

The first metatarsal is the shortest, thickest and stoutest of all the metatarsals. It has a strong shaft & of marked prismoid form. The base of the bone has an oval lateral facet that is an ill-defined smooth area to articulate the second metatarsal. The proximal surface of the base is large, kidney shaped and indented on medial & lateral margins to articulate medial cuneiform. The circumference of it is grooved to attach the tarsometatarsal ligaments. The head is large, has a plantar elevation, a crista that separates 2 grooved facets where the small sesamoid bones glide.

SECOND METATARSAL

The second metatarsal is the longest and is broad & rough below the base. The base has four articulating facets. The proximal facet is concave and triangular to articulate intermediate cuneiform. The dorsomedial facet is variable in size and articulates medially and some part of intermediate cuneiform. There are two lateral facets; dorsal (upper) & plantar (lower) which are separated by a nonarticular bone. Each of these facets are divided into 2 vertical ridge, 2 anterior facets to articulate with the third metatarsal and two posterior facets that articulate with the lateral cuneiform.

THIRD METATARSAL

The third metatarsal has a smooth, flat triangular base that articulates proximally with the lateral cuneiform. The lateral side of the base has one facet which is placed dorsally to articulate with the 4^th metatarsal bone. The medial side of the base has 2 facets for second metatarsal bone. The medial plantar facet is mostly absent. The third tarsometarsal joint is relatively immobile.

FOURTH METATARSAL

The fourth metatarsal is smaller than the third. The base of it is quadrilateral to articulate cuboid. The lateral side of the base has a single facet dorsally to articulate with the fifth metatarsal bone. The medial side of the base is smooth to articulate third metatarsal bone.

FIFTH METATARSAL

The fifth metatarsal has a rough eminence, tuberosity on the lateral side of the base. The base articulates with cuboid proximally in a triangular and oblique surface; medially with the fourth metatarsal. The lateral side of the base has a tuberosity or the styloid process which projects backwards and laterally. The plantar surface of the base is grooved by the tendon of abductor digiti minimi and origin of flexor digiti minimi brevis.

MUSCLE ATTACHMENTS

The 1^st metatarsal attaches tendon of tibialis anterior medially and tendon of fibularis longus on the plantar aspect. It gives origin to medial head of 1^st dorsal interosseous on proximal aspect of lateral surface.

The 2^nd metatarsal attaches lateral head of first dorsal interosseous & medial head of second dorsal interosseous respectively to the medial and lateral surface of the shaft of the bone.

The 3^rd metatarsal attaches lateral heads of second dorsal interosseous and first plantar interosseous to the medial surface of the shaft. The medial head of the third dorsal interosseous is attached to the lateral surface.

The 4^th metatarsal attaches the lateral head of the third dorsal and second plantar interosseous are attached to the medial surface. The medial head of the fourth dorsal interosseous is attached to the lateral surface of the bone.

The 5^th metatarsal has attachment of fibularis tertius to the medial part of the surface and medial border of the shaft. The fibularis brevis attaches to the dorsal surface of the tuberosity. A strong band of the plantar aponeurosis, sometimes containing muscle, connects the apex of the tuberosity to the lateral process of the calcaneal tuberosity. The lateral heads of fourth dorsal and third plantar interosseous are attached to the medial side of the shaft.

VASCULAR SUPPLY

All the metatarsals are supplied by first dorsal and plantar metatarsal arteries. A nutrient artery enters the lateral surface of mid diaphysis in all metatarsals.

NERVOUS SUPPLY

The first & second metatarsal has nervous supply from the branches of deep fibular and medial plantar nerves. The third & fourth metatarsal is innervated by branches of the deep fibular and lateral plantar nerves. The fifth metatarsal is innervated from the branches of sural, superficial fibular and lateral plantar nerves.

OSSIFICATION

Each metatarsal ossifies from 1 primary and 1 secondary center. The primary center appears in shaft at 10^th week of gestational life in first metatarsal and at 9^th week it appears in the rest of the metatarsals. The secondary center appears in the base of first metatarsal in the 3^rd year and in rest of the bones it appears around 3^rd-4^th year. Both the centers unite by 18^th year.

 

TARSAL BONES

 

Tarsal bones are made up of seven bones which are arranged in two rows. In the proximal row talus is above and calcaneum is below. In the distal row there are four tarsal bones in a line, so from medial to lateral are medial cuneiform, intermediate cuneiform, lateral cuneiform and cuboid. Navicular is between talus and the three cuneiforms. The tarsals are stronger larger than the carpals as they have to support and distribute the body weight. The tarsals occupy half of the foot.

The tarsals and metatarsals are arranged to form intersecting and longitudinal arches of the foot. So they absorb thrust and weight hence which doesn’t transmit to tibia from the ground. The tarsal bones are in cuboidal form and has 6 surfaces.

CALCANEUM

Calcaneum is the largest bone and is held horizontally of the tarsals. It forms the prominence of the heel. Its long axis is directed forwards, upwards and laterally. It has a thin cortex. Calcaneum is roughly cuboidal and has 6 surfaces.

The anterior surface is the smallest surface of the bone. It is covered by a concavoconvex articular surface for cuboid.

The plantar surface is rough and marked by 3 tubercles. The medial and lateral tubercles are posteriorly which are part of calcaneum tuberosity & anterior tubercle is situated at the anterior part. The medial and lateral tubercles are separated by a notch. Medial tubercle is longer and broader than the lateral tubercle. Anterior tubercle has attachment of long plantar ligament.

The lateral surface is rough and mostly flat. It is proximally deeper and palpable on the lateral aspect of the heel distal to the lateral malleolus. At the lower end in the anterior part it presents a small elevation known as peroneal trochlea or tubercle. It bears an oblique groove for the tendon of fibularis longus and a shallower proximal groove for the tendon of fibularis brevis. About 1 cm or more behind and above the fibular trochlea, a second elevation may exist for attachment of the calcaneofibular part of the lateral ligament.

The posterior surface is divided into 3 areas; upper, middle and lower. The upper area is smooth and is separated from the calcaneal tendon by bursa and adipose tissue. The middle area is rough, largest and limited by the groove from above and from below by a rough ridge for calcaneal tendon. The lower area is rough, vertically striated and is inclined downwards and forwards also it is subcutaneous weight bearing surface.

The medial surface is concave and downwards. The concavity is accentuated by the sustentaculum tali that projects medially from the distal part of its upper border like a shelf. The upper surface of this projection assists in the formation of talocalcaneonavicular joint. Its lower surface is grooved; and the medial margin is in the form of a rough strip convex from before backwards.

The superior or proximal surface is divisible into three areas. The posterior third is rough and concavo-convex, supporting fibroadipose tissue (Kager’s fat pad) between the calcaneal tendon and ankle joint. The middle third carries the posterior talar facet, which is oval and convex anteroposteriorly. The anterior third is partly articular, with a rough depression (calcaneal sulcus) narrowing into a groove on the medial side, completing the tarsal sinus with the talus. Distal and medial to this groove, an elongated articular area covers the sustentaculum tali (talar shelf) and extends distolaterally on the bone. This facet is often divided into middle and anterior talar facets by a non-articular interval at the anterior limit of the sustentaculum tali. Rarely, all three facets on the upper surface of the calcaneus are fused into one irregular area.

Muscle & Ligamentous Attachments

1. Posterior Surface:
• Middle rough area: Insertion of tendocalcaneus and plantaris.
• Upper area: Covered by a bursa.
• Lower area: Covered by dense fibrofatty tissue, supports body weight while standing, similar to ligamentum patellae attachment.
2. Anterior Dorsal Surface:
• Lateral nonarticular area:
• Origin of extensor digitorum brevis.
• Attachment to the stem of the inferior extensor retinaculum.
• Attachment to the stem of the bifurcate ligament.
• Medial nonarticular area:
• Forms sulcus calcanei.
• Attachment to interosseous talocalcanean ligament (medially) and cervical ligament (laterally).
3. Plantar Surface:
• Medial tubercle:
• Origin for abductor hallucis (medially).
• Attachment to flexor retinaculum (medially).
• Origin to flexor digitorum brevis (anteriorly).
• Attachment to plantar aponeurosis (anteriorly).
• Lateral tubercle: Origin for abductor digiti minimi.
• Anterior tubercle and rough area: Attachment to short plantar ligament.
• Rough strip between tubercles: Attachment to long plantar ligament.
4. Lateral Surface:
• Peroneal tubercle: Between tendons of peroneus brevis (above) and peroneus longus (below).
• Trochlea: Attachment to a slip from the inferior peroneal retinaculum.
• Calcaneofibular ligament: Attached about 1 cm behind the peroneal trochlea.
5. Medial Surface:
• Groove on lower surface of sustentaculum tali: Occupied by tendon of flexor hallucis longus.
• Medial margin of sustentaculum tali: Related to tendon of flexor digitorum longus, provides attachment to:
• Spring ligament (anteriorly).
• Slip from tibialis posterior (middle).
• Superficial fibres of deltoid ligament (whole length).
• Medial talocalcanean ligament (posteriorly).
• Below groove for flexor hallucis longus: Origin for medial head of flexor digitorum accessorius.

• Calcaneal Sulcus: Attachment for interosseous talocalcanean and cervical ligaments, and medial root of inferior extensor retinaculum.
• Nonarticular Area Distal to Posterior Talar Facet: Attachment for extensor digitorum brevis (part), principal band of inferior extensor retinaculum, and stem of bifurcate ligament.
• Medial Process of Calcaneal Tuberosity:
• Attachment for abductor hallucis, superficial part of flexor retinaculum, plantar aponeurosis, and flexor digitorum brevis.
• Primary weight-bearing portion, often associated with plantar fasciitis.
• Lateral Process of Calcaneal Tuberosity: Attachment for abductor digiti minimi, extending medially.
• Long Plantar Ligament: Attached to rough region between processes, extends to anterior tubercle.
• Plantar Calcaneocuboid Ligament: Attached to tubercle and area distal to it.
• Lateral Tendinous Head of Flexor Accessorius: Attached distal to lateral process near long plantar ligament.
• Posterior Surface: Attachment for plantaris near medial side of calcaneal tendon.
• Anterior Lateral Surface: Crossed by fibular tendons, largely subcutaneous.
• Calcaneofibular Ligament: Attached 1-2 cm proximal to fibular trochlea.
• Dorsal Surface of Sustentaculum Tali: Part of talocalcaneonavicular joint.
• Plantar Surface of Sustentaculum Tali: Grooved by tendon of flexor hallucis longus, margins give attachment to deep part of flexor retinaculum.
• Plantar Calcaneonavicular Ligament: Attached distally to medial margin of sustentaculum.
• Proximal Attachments: Slip from tibialis posterior, superficial fibres of deltoid ligament, and medial talocalcaneal ligaments.
• Distal Attachments: Tendon of flexor digitorum longus related to margin of sustentaculum tali, may groove it.
• Medial Head of Flexor Accessorius: Attached distal to groove for flexor hallucis longus.

 

Vascular & Nervous Supply

The calcaneum receives its blood supply from medial and lateral calcaneal arteries, fibular artery, posterior calcaneal aponeurosis and medial & lateral plantar arteries.

The calcaneus is innervated by the branches of tibial, sural and deep fibular nerves.

 

Ossification

The ossification of calcaneus has 1 primary center and 1 secondary center. The primary center appears during the 3rd month of gestational life. The secondary center appears between 6th – 8th year and appears in a scale like epiphysis on the posterior surface and fuses with rest of the bone by 14th – 16th year.

 

TALUS

The talus is the 2nd largest tarsal bone. It is one of the bones of human body which has the highest percentage of surface area covered by the articular cartilage. The talus has a retrograde blood supply wherein arterial blood enters the bone at the distal end. It is an intercalated bone with no tendinous attachments and is a link between foot and leg via ankle joint. Talus is held horizontally with head anteriorly, neck and body posteriorly.

Head

The head of talus is directed forwards and slightly downwards and medially. The distal or the anterior surface of the head of talus is large, oval and convex where there is articular surface for the proximal navicular bone.

The inferior or plantar surface is marked by 3 articular areas which are separated by indistinct and smooth ridges. The posterior facet is the largest, oval and slightly convex which articulates with the middle facet on sustentaculum tali of calcaneum. The anterolateral facet articulates with the anterior facet of the calcaneum. The middle facet articulates with spring ligament and fibrocartilage. Hence when foot is inverted passively, dorsolateral aspect is palpable and visible; it is hidden when toes are dorsiflexed.

Neck

The neck of the talus is narrow and anteromedially between head and body. The plantar surface medially has a deep sulcus tali, articulates with calcaneus and forms a roof known as tarsal sinus which is occupied by interosseous talocalcaneal and cervical ligaments. The long axis of the neck of talus directed downwards, forwards and medially has a neck body angle of 130 - 140° in infants and 150° in adults. The smaller the angle in children accounts for inverted position of their feet. The medial articular facet of talus and a part of trochlear surface extends onto the neck. A dorsolateral known as squatting facet is commonly present on the talar neck in individuals who have a habit of squatting position; it articulates with the anterior tibial margin in extreme dorsiflexion.

Body

The body of talus is cuboidal in shape and is covered by trochlear surface articulating with the distal end of tibia. The body has 5 surfaces; lateral, medial, superior, inferior and posterior.

The superior surface or trochlear surface bears articular surface that articulates with lower end of tibia. The surface is convex from before backwards and concave from side to side. It is broader anteriorly than posteriorly. The medial border is straight and lateral border is directed forwards and laterally.

The inferior surface is having two articular surfaces; posterior calcaneal and middle calcaneal. These surfaces are separated by a groove known as sulcus tali. The groove runs obliquely forwards and laterally. The groove becomes broader gradually and deeper in front. In the hindfoot articulating surface lies above such a groove upon the upper surface of the calcaneus and forms a canal known as sinus tarsi that lies in interosseous talocalcaneal ligament.

The medial surface in its upper part has a pear-shaped articular facet for the medial malleolus. It continues above with trochlea and below with the rough depression which articulates deep part of deltoid ligament to the ankle joint.

The posterior surface is an articulating surface which is large and oval. It also articulates with upper surface of calcaneus and is concave in its long axis which runs forward and laterally at an angle of 45 degrees with the medial plane. The middle calcaneal articular surface is small, oval and convex that articulates with upper surface of sustentaculum tali of calcaneus.

The lateral surface carries a large triangular facet, concave from above downwards to articulate with lateral malleolus. The anterior half is continuous above with trochlea and in front of it is rough depression for the attachment of anterior talofibular ligament.

Vascular Supply

The talus has a limited blood supply due to its lack of muscle attachments. Its primary blood sources are the posterior tibial, dorsalis pedis, and fibular arteries.

The artery of the tarsal canal is crucial. It originates from the posterior tibial artery and enters the tarsal canal. Here, it forms an anastomosis with the artery of the tarsal sinus, creating a vascular sling under the talar neck. Branches from these arteries supply different parts of the talus.

The deltoid branch of the artery of the tarsal canal is particularly important as it is often the sole blood supply to the talus after a fracture. The dorsalis pedis artery also contributes significantly to talar blood flow. While the fibular artery supplies some branches, its contribution is minimal.

Overall, the talar blood supply is complex and essential for understanding potential complications related to talar injuries.

Ossification

There is only single ossification center which appears at 6 months in intra uterine life.

NAVICULAR

The bone is a boat shaped which is situated on the medial side of the foot, in front of head of talus and behind the 3 cuneiforms. Navicular has 6 surfaces. The anterior surface is convex and is divided into 3 facets for cuneiforms to articulate. The posterior surface is concave and oval to articulate head of talus. The posterior surface is broader laterally than medially. The dorsal surface is broad, rough, non-articular and convex from side to side. The medial surface has a blunt and prominent tuberosity which is downwards, tuberosity is separated from plantar surface by a groove. The medial surface has attachment of spring ligament and insertion of posterior tibial tendon. The lateral surface is rough and irregular but frequently has a facet for cuboid.

Muscle Attachments

The navicular tuberosity is main attachments of tibialis posterior. The plantar calcaneonavicular ligament is attached to a slight projection lateral to the groove. The calcaneonavicular is a part of bifurcate ligament is attached to the rough part of lateral surface.

Vascular Supply

The dorsal part of navicular is supplied from the dorsalis pedis artery. The medial plantar artery supplies plantar aspect of the bone.

Nervous Supply

The navicular is innervated by deep fibular and medial plantar nerves.

Ossification

It ossifies from one center at the 3^rd year of life in females and 4^th year in males.

CUBOID

The cuboid is the lateral most bone in the distal row of tarsal bones. It roughly cuboidal in shape. It is situated in front of calcaneum and behind 4^th & 5^th metatarsal bone. It is held anteroposteriorly. The cuboid has 6 surfaces.

The dorsal surface is directed upwards and laterally, and is rough for the ligaments attachments.

The plantar surface has a deep groove in front of it known as peroneus sulcus that runs obliquely forwards and medially. It lodges the tendon of the peroneus longus and is bounded by prominent ridge to which long plantar ligament is attached. The ridge ends laterally at the tuberosity where there is an oval facet that glides on the sesamoid bone or cartilage of tendon of peroneus longus. The surface of bone behind groove is rough and has many attachments of ligaments.

The lateral surface has deep notch by the commencement of peroneal sulcus.

The posterior surface is smooth, triangular and concavoconvex that articulates with distal calcaneal surface; its medial plantar angle projects proximally and inferiorly to the distal end of calcaneus.

The anterior surface is of small in size, irregular and triangular. The surface is divided by vertical ridge into 2 facets forming 4^th & 5^th tarsometatarsal joints.

The medial surface is broad, irregularly quadrilateral, has a middle & upper part of smooth oval facet to articulate the 3^rd cuneiform. At the back of them is a smaller facet to articulate navicular that is rough to attach strong interosseous ligaments.

Muscle Attachments

Its dorsal surface serves as an attachment point for multiple ligaments, including the calcaneo-cuboid, cubonavicular, cuneocuboid, and cubometatarsal ligaments.

On its plantar surface, the cuboid connects to the deep fibers of the long plantar ligament and receives attachments from the tibialis posterior and flexor hallucis brevis tendons. The medial side of the bone articulates with several ligaments, including the interosseous, cuneocuboid, cubonavicular, and medial calcaneocuboid ligaments.

Due to its trapezoidal shape and position, the cuboid functions as the keystone of the foot's lateral longitudinal arch. Its role in stabilizing the foot is evident during movement, as tension in the calcaneocuboid joint helps lock the midtarsal joint.

Vascular & Nervous Supply

Cuboid is supplied by deep branches of medial & lateral plantar arteries and branches of dorsal arterial network. It is innervated by branches of lateral plantar, sural and deep fibular nerves.

Ossification

The primary ossification center appears just before birth.

CUNEIFORMS

There are three cuneiforms are wedge shaped. There are 3 cuneiforms; medial, intermediate and lateral. They are located between navicular and first three metatarsals & medial to cuboid bone. The dorsal surface of intermediate and lateral cuneiforms forms the base of the wedge. The wedge is reversed in medial cuneiform. The proximal surface of all the 3 cuneiforms form concavity for distal surface of navicular. The medial and lateral cuneiforms project distally beyond the intermediate cuneiform and so form a recess or mortise for the second metatarsal base.

MEDIAL CUNEIFORM

The medial cuneiform is the largest of the cuneiforms. The medial cuneiform articulates with navicular and base of the first metatarsal. The dorsal surface is rough and narrow, also is directed upwards and laterally to attach the ligaments. The distal surface is a kidney shaped facet for the base of first metatarsal with its hilum directed laterally. The proximal surface has a piriform facet to articulate navicular which is concave, vertically and dorsally narrowed. The plantar surface is formed by the base of the wedge and its back has a tuberosity for the insertion of part of tendon of tibialis posterior and part of tendon of tibialis anterior. The lateral surface is concave, partly nonarticular and has a smooth right-angled strip along its proximal and dorsal margins for intermediate cuneiform. The rest of the surface is rough for attachments of ligaments.

INTERMEDIATE CUNEIFORM

The intermediate (middle) cuneiform is the smallest of the cuneiforms and has a wedge-shaped dorsal base and apex plantar. It articulates proximally with navicular and distally with 2^nd metatarsal bone. The distal and proximal surfaces are both triangular articular facets. The medial surface is somewhat articular which is smooth and angled region that is sometimes doubled with medial cuneiform. The lateral surface is also somewhat articular; along its proximal margin a vertical segment, it is usually indented and next to it is lateral cuneiform. The plantar surface is formed by the edge of the wedge.

LATERAL CUNEIFORM

The lateral cuneiform lies between intermediate cuneiform and cuboid. It articulates with navicular and base of 3^rd metatarsal. The dorsal surface is rough and rectangular; it is a base of the wedge. The plantar surface is narrow. The distal surface is a triangular articular facet for 3^rd metatarsal base. The proximal surface is rough at the plantar aspect but the dorsal 2/3^rd articulates with the navicular. The medial surface is partly non articular and has a vertical segment indented by intermediate cuneiform. On its proximal margin, distal margin and a narrow strip articulates with lateral side of 2^nd metatarsal base. The lateral surface is also partly nonarticular and has an oval proximal facet for cuboid. A semilunar facet on its dorsal and distal margin articulates with the dorsal part of medial side of 4^th metatarsal base.

Muscle Attachments

Most of the part of tibialis anterior is inserted to an impression on the anteroinferior angle of medial surface of medial cuneiform. The plantar surface of medial cuneiform has a slip of tibialis posterior. On the lateral surface of medial cuneiform there is insertion of peroneus longus into rough anteroinferior part.

The plantar surface of intermediate cuneiform has an attachment of tibialis posterior.

The plantar surface of lateral cuneiform has a slip from the tendon of tibialis posterior and sometimes of flexor hallucis brevis.

Vascular Supply

The medial cuneiform is supplied via its dorsal, medial and lateral surfaces, mainly from the dorsal arterial network.

The intermediate cuneiform is supplied via its dorsal, medial and lateral surfaces, mainly from the dorsal arterial network.

The lateral cuneiform is supplied via its dorsal, medial and lateral surfaces, mainly from the dorsal arterial network.

Nervous Supply

The medial cuneiform is supplied by the deep fibular and medial plantar nerves. The intermediate cuneiform is innervated by the deep fibular and medial plantar nerves. The lateral cuneiform is innervated by branches of the deep fibular and lateral plantar nerves.

Ossification

Each cuneiform bone ossifies from one centre, which appears during the first year in the lateral cuneiform, during the second year in the medial cuneiform, and during the third year in the intermediate cuneiform bone.

 

 WRITTEN & COMPLIED BY Dr. Palak Shah