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