EDITOR'S NOTE: The following is a small sample of the Interactive Foot and Ankle CD in the ground breaking Primal Pictures 3-D Anatomy CD ROM series.
Dorsal Digital Expansions
There are four dorsal digital expansions in the foot, one for each of the lateral four toes. Each dorsal digital expansion is a flattened, distal continuation of the tendon of extensor digitorum longus for that toe and commences dorsal to the corresponding metatarsophalangeal joint. Dorsal to the proximal phalanx, each digital expansion splits longitudinally into three slips: a central (or axial) slip and two collateral slips.
The axial slip crosses the dorsal aspect of the proximal interphalangeal joint, blending with its fibrous capsule before inserting onto the dorsal surface of the base of the middle phalanx.
The two collateral slips cross the proximal interphalangeal joint on either side of the axial slip and unite before inserting onto the dorsal aspect of the base of the distal phalanx.
The collateral slips of the dorsal extensor expansions receive extensions from the appropriate plantar and dorsal interosseous muscles.
The dorsal digital expansions to the 2nd, 3rd and 4th toes receive, in addition, the tendons of extensor digitorum brevis.
Each lumbrical tendon is attached to the medial aspect of the digital expansion of the corresponding toe. It is significant that the attachment of the lumbrical tendon to the digital expansion is distal to the point of attachment of any of the interossei.
Because the extensor expansions insert onto the middle as well as distal phalanges, muscular action effects extension both at the proximal and distal interphalangeal joints.
Distal Phalanx of Great Toe
The distal plalanx of the great toe is a miniature long bone and comprises a base proximally, a head distally and an intervening shaft. The base of the distal phalanx of the hallux articulates with the head of the proximal phalanx. The dorsal aspect of the base of the distal phalanx receives the insertion of the tendon of extensor hallucis longus, while the plantar aspect of the base receives the insertion of the tendon of flexor hallucis longus. Tubercles on either side of the base provide attachment for the collateral ligaments of the interphalangeal joint
Extensor Digitorum Longus
Proximally, the extensor digitorum longus arises contiguously from the inferior aspect of lateral tibial condyle, upper three-fourths of the medial (extensor) surface of fibula, anterior surface of interosseous membrane, anterior intermuscular septum and from the overlying deep fascia.
The extensor digitorum longus muscle becomes tendinous in the distal part of the leg. The tendon passes over the anterior aspect of the ankle joint lateral to the tendon of extensor hallucis longus. The tendon of extensor digitorum longus then splits into four slips beneath the inferior extensor retinaculum. The four slips (one for each of the lateral four toes) diverge on the dorsum of the foot and insert onto the dorsal aspects of the middle and distal phalanges of the corresponding toes, via the dorsal digital expansions.
- Nerve Supply: Deep peroneal nerve (L4, L5 and S1)
- Action: Extensor digitorum longus, extends the lateral four toes at the interphalangeal and metatarsophalangeal joints and assists in dorsiflexion of the ankle.
Extensor Digitorum Brevis
Extensor digitorum brevis is an intrinsic muscle of the foot and the only one to be situated on the dorsum of the foot. It lies deep to the tendons of extensor digitorum longus. The belly of the muscle can be palpated inferomedial to the lateral malleolus on the dorsum of the foot
Proximally, extensor digitorum brevis originates from the anterolateral part of the upper surface of the calcaneus and contiguously from an adjacent area on the lateral calcaneal surface. The muscle also takes attachment from the stem of the inferior extensor retinaculum that overlies it.
From its origin, the muscle runs in a distomedial direction on the dorsum of the foot and gives rise to four tendons, one for each of the medial four toes. The most medial of the four tendons is that of extensor hallucis brevis; it attaches to the dorsal aspect of the base of the proximal phalanx of the hallux. The next three tendons attach, in sequence, to the lateral aspects of the extensor digitorum longus tendons to the 2nd, 3rd and 4th toes.
- Nerve Supply: Deep peroneal (L5 and S1)
- Action: Assists extensor hallucis longus in dorsiflexion of the hallux at the proximal interphalangeal joint and assists extensor digitorum longus in dorsiflexing the 2nd, 3rd and 4th toes.
The smallest of three wedge-shaped bones that lie between the distal aspect of the navicular and the medial three metatarsals. It articulates with the navicular proximally and with the base of the 2nd metatarsal distally. In addition, it articulates with the medial cuneiform medially and the lateral cuneiform laterally. It is wide and square on its dorsal surface and narrow on its plantar aspect. The dorsal and plantar aspects are roughened for the attachments of a number of interosseous ligaments. The plantar surface receives a small slip of insertion of tibialis posterior and gives attachment to part of the origin of flexor hallucis brevis.
The calcaneus is the largest and most plantar of the tarsal bones and forms the heel of the foot. It is an irregularly cuboidal bone presenting six surfaces: the superior surface articulates with the talus; the distal surface articulates with the cuboid; the medial surface has a shelf-like projection called the sustentaculum tali, which supports the head of the talus; the lateral surface features the peroneal trochlea, which separates the tendons of peroneus longus and brevis; the posterior surface receives the tendo calcaneus; and the inferior surface is roughened posteriorly and forms the major weightbearing area of the calcaneus. This surface provides attachment for the plantar aponeurosis, several plantar muscles and ligaments.
The calcaneus articulates with the cuboid and talus and embryologically forms the posterior part of the lateral column of the foot. It is often fractured by direct vertical force, as when landing on the heel in a fall from a height. When the calcaneus is fractured in this manner, there is a loss of height of the bone, broadening of the heel, and there are classical intra-articular fracture patterns. Radiologically, Bohler's angle is markedly decreased and may in some instances be reversed.
Calcaneus: Superior Surface
The upper surface of the calcaneus presents three articular facets as follows:
- Occupying the middle third of the upper surface of the calcaneus is the posterior talar facet. This is an oval, smooth and convex facet with its long axis running obliquely in a distolateral direction. It engages a reciprocally concave facet on the inferior surface of the talar body to form the subtalar talocalcaneal joint.
- Anteromedial to the posterior articular facet and occupying the entire upper surface of the sustentaculum tali is an elongated and concave facet, also with its long axis running in a distolateral direction. This is the middle talar facet. It is part of the talocalcaneonavicular joint and engages the inferomedial aspect of the talar head.
- Immediately anterolateral to the middle talar facet and often confluent with it is the anterior talar facet. It is part of the talocalcaneonavicular joint and engages the inferolateral aspect of the talar head.
Situated on the upper surface of the calcaneus in front of the posterior talar facet and behind the middle and anterior talar facets is the sulcus calcanei, an obliquely disposed groove. The sulcus calcanei gives attachment to the interosseous talocalcaneal ligament.
The upper surface of the calcaneus, anterior to the lateral end of the sulcus calcanei, gives attachment to the cervical ligament, bifurcate ligament, the origin of extensor digitorum brevis and the stem of the inferior extensor retinaculum.
Behind the posterior talar facet on the upper surface of the calcaneus is a somewhat rough, non-articular area, which is covered by fibrous and adipose tissue and represents the interval between the tendo calcaneus posteriorly and the ankle joint anteriorly.