Attachments

No muscles are attached to the distal tibia. The interosseous ligament, the deltoid ligament, and the anterior and posterior tibiofibular ligaments are attached to the distal tibia.

Vascular supply

The distal tibia is supplied by an arterial network formed by branches of the dorsalis pedis, posterior tibial and fibular arteries.

Innervation

The distal tibia is innervated by branches from the deep fibular, posterior tibial, saphenous and sural nerves.

Attachments

No muscles are attached to the distal fibula below the level of the interosseous ligament. The ligamentous attachments are those of the lateral ligament complex, i.e. the anterior talofibular, the calcaneofibular and the posterior talofibular ligaments. The interosseous ligament is attached on its medial aspect.

Vascular supply

The distal fibula is supplied by an arterial network made up of branches of the dorsalis pedis, posterior tibial and fibular arteries.

Innervation

The distal fibula is innervated by the deep fibular, tibial, saphenous and sural nerves.

Head

Directed distally and somewhat inferomedially, the head has a distal surface which is ovoid and convex; its long axis is also inclined inferomedially to articulate with the proximal navicular surface. The plantar surface of the head has three articular areas, separated by smooth ridges. The most posterior and largest is oval, slightly convex and rests on a shelf-like medial calcaneal projection, the sustentaculum tali. Anterolateral to this and usually continuous with it, a flat articular facet rests on the anteromedial part of the dorsal (proximal) calcaneal surface; distally it continues into the navicular surface. Between the two calcaneal facets, a part of the talar head, covered with articular cartilage, is in contact with the plantar calcaneonavicular ligament, which is covered here, superiorly, by fibrocartilage (see Fig. 84.15A,B). When the foot is inverted passively, the dorsolateral aspect of the head is visible and palpable approximately 3 cm distal to the tibia; it is hidden by extensor tendons when the toes are dorsiflexed.

Fig. 84.15 A, Disarticulated talocalcaneal and talocalcaneonavicular joints, seen from above. B, Disarticulated talus (seen from below).

(From Sobotta 2006.)

Neck

The neck is the narrow, medially inclined region between the head and body. Its rough surfaces are for ligaments. The medial plantar surface has a deep sulcus tali which, when the talus and calcaneus are articulated, forms a roof to the sinus tarsi, which is occupied by inter-osseous talocalcaneal and cervical ligaments.

The long axis of the neck, inclined downwards, distally and medially, makes an angle of approximately 150° with that of the body; it is smaller (130–140°) at birth, accounting in part for the inverted foot in young children. The dorsal talonavicular ligament and ankle articular capsule are attached distally to its dorsal surface. Thus the proximal part of this surface lies within the capsule of the ankle joint. The medial articular facet of the talar body and part of the trochlear surface may extend onto the neck. The anterior talofibular ligament is attached on the lateral aspect of the neck, spreading along the adjacent anterior border of the lateral surface. The interosseous talocalcaneal and cervical ligaments are attached to the inferior surface of the neck. A dorsolateral, so-called ‘squatting facet’ is commonly present on the talar neck in those individuals who habitually adopt the squatting position: it articulates with the anterior tibial margin in extreme dorsiflexion and may be double.

Body

The body is cuboidal, covered dorsally by a trochlear surface articulating with the distal end of the tibia. It is anteroposteriorly convex, gently concave transversely, widest anteriorly and, therefore, sellar. The triangular lateral surface is smooth and vertically concave for articulation with the lateral malleolus. Superiorly, it is continuous with the trochlear surface; inferiorly its apex is a lateral process. Proximally, the medial surface is (posterosuperiorly) covered by a comma-shaped facet, which is deeper in front and articulates with the medial malleolus. Distally, this surface is rough and contains numerous vascular foramina. The small posterior surface features a rough projection termed the posterior process. The process is marked by an oblique groove between two tubercles which lodges the tendon of flexor hallucis longus. The lateral tubercle is usually larger; the medial is less prominent and immediately behind the sustentaculum tali (Fig. 84.8A). The plantar surface articulates with the middle one-third of the dorsal calcaneal surface by an oval concave facet, its long axis directed distolaterally at an angle of approximately 45° with the median plane. The medial edge of the trochlear surface is straight, but its lateral edge inclines medially in its posterior part and is often broadened into a small elongated triangular area which is in contact with the posterior tibiofibular ligament in dorsiflexion.

Fig. 84.8 Skeleton of the foot. A, Foot bones. B, Calcaneus. C, Talus.

(From Drake, Vogl, Mitchell, Tibbitts and Richardson 2008.)

The posterior talofibular ligament is attached to the lateral tubercle of the posterior process. Its attachment extends up to the groove, or depression, between the process and posterior trochlear border. The posterior talocalcaneal ligament is attached to the plantar border of the posterior process. The groove between the tubercles of the process contains the tendon of flexor hallucis longus and continues distally into the groove on the plantar aspect of the sustentaculum tali. The medial talocalcaneal ligament is attached below to the medial tubercle, whereas the most posterior superficial fibres of the deltoid ligament are attached above the tubercle. The deep fibres of the deltoid ligament are attached still higher to the rough area immediately below the comma-shaped articular facet on the medial surface (Fig. 84.8A,C).

Muscle attachments

No muscles are attached to the talus. However, many ligaments are attached to the bone, and these confer stability to the ankle, subtalar and talocalcaneonavicular joints (Fig. 84.8A–C).

Vascular supply

The talar blood supply is rather tenuous because of the lack of muscle attachments. The first comprehensive account of talar blood supply was provided by Wildenauer in 1950. The extraosseous blood supply is via the posterior tibial, dorsalis pedis and fibular arteries (Fig. 84.9). The ‘artery of the tarsal canal’ arises from the posterior tibial artery approximately 1cm proximal to the origin of the medial and lateral plantar arteries (Fig. 84.10) and passes anteriorly between the sheaths of flexor digitorum longus and flexor hallucis longus to enter the tarsal canal in which it lies anteriorly, close to the talus. (The ‘tarsal canal’ is the term that is commonly used to describe the tunnel-shaped medial end of the sinus tarsi.) Branches from the arterial network in the tarsal canal enter the talus. The artery continues through the tarsal canal into the lateral part of the tarsal sinus, where it anastomoses with the artery of the tarsal sinus, forming a vascular sling under the talar neck. A branch of the artery of the tarsal canal known as the deltoid branch passes deep to the deltoid ligament and supplies part of the medial aspect of the talar body. Sometimes it arises from the posterior tibial artery; rarely, it arises from the medial plantar artery. In talar fractures it may be the only remaining arterial supply to the talus to maintain the viability of the talar body. The dorsalis pedis artery supplies branches to the superior aspect of the talar neck and also gives off the artery of the tarsal sinus. This large vessel is always present and anastomoses with the artery of the tarsal canal. The artery of the tarsal sinus receives a contribution from the anterior perforating branch of the fibular artery and supplies direct branches to the talus. The fibular artery provides small branches which form a plexus of vessels posteriorly with branches of the posterior tibial artery, however, the contribution that the fibular artery makes to the talar blood supply is thought to be insignificant.

Fig. 84.9 The arterial anastomoses of the ankle, tarsus and metatarsus.

Fig. 84.10 Branches of the posterior tibial artery, posteromedial view of ankle.

The intraosseous blood supply of the talar head comes medially from branches of the dorsalis pedis and laterally via vessels that arise from the anastomosis between the arteries of the tarsal canal and tarsal sinus. The middle one-third of the talar body, other than its most superior aspect, and the lateral one-third, other than its posterior aspect, are supplied mainly by the anastomotic arcade in the tarsal canal. The medial one-third of the talar body is supplied by the deltoid branch of the artery of the tarsal canal.

Innervation

The talus is innervated by branches from the deep fibular, posterior tibial, saphenous and sural nerves.

Ossification

A single ossification centre appears prenatally at 6 months (Fig. 84.7). The posterior process (Stieda’s process) is a separate bone in 5% of individuals and arises from a separate ossification centre, which appears between 8 and 11 years. In athletes and dancers, it may be susceptible to impingement against the posterior tibia, resulting in pain and sometimes requires surgical removal. Another accessory bone (although rare) is the os supratalare, which lies on the dorsal aspect of the talus; it rarely measures more than 4 mm in length.

Talar fractures

The talus has no muscular attachments and 70% of its surface is covered by articular cartilage: displaced talar neck fractures, where the blood supply to the talar body is interrupted, can therefore result in avascular necrosis and non-union. In general, these complications do not occur in undisplaced fractures. If a subchondral lucency is seen in the talar dome on radiographs at 8 weeks after fracture of the talar neck (Hawkin’s sign), it may be assumed that vascularity to the talar body is intact and that the fracture is likely to heal satisfactorily.

Muscle and ligament attachments

The interosseous talocalcaneal and cervical ligaments and the medial root of the inferior extensor retinaculum are attached in the calcaneal sulcus. The non-articular area distal to the posterior talar facet is the site of attachment of extensor digitorum brevis (in part), the principal band of the inferior extensor retinaculum and the stem of the bifurcate ligament.

Abductor hallucis and the superficial part of the flexor retinaculum and, distally, the plantar aponeurosis and flexor digitorum brevis, are all attached to the medial process of the calcaneal tuberosity at its prominent medial margin. Abductor digiti minimi is attached to the lateral process, extending medially to the medial process. The long plantar ligament is attached to the rough region between the processes proximally, and extends to the anterior tubercle distally. The short plantar ligament is attached to the tubercle and the area distal to it. The lateral tendinous head of flexor accessorius is attached distal to the lateral process near the lateral margin of the long plantar ligament. Plantaris is attached to the posterior surface near the medial side of the calcaneal tendon. The anterior part of the lateral surface is crossed by the fibular tendons, but is largely subcutaneous. The calcaneofibular ligament is attached 1–2 cm proximal to the fibular trochlea, usually to a low, rounded elevation.

The dorsal surface of the sustentaculum tali is part of the talocalcaneonavicular joint; its plantar surface is grooved by the tendon of flexor hallucis longus and margins of the groove give attachment to the deep part of the flexor retinaculum. The plantar calcaneonavicular ligament is attached distally to the medial margin of the sustentaculum, which is narrow, rough and convex. A slip from the tendon of tibialis posterior, and superficial fibres of the deltoid ligament and medial talocalcaneal ligaments, are attached proximally. Distal to the attachment of the deltoid ligament, the tendon of flexor digitorum longus is related to the margin of the sustentaculum and may groove it. The large medial head of flexor accessorius is attached distal to the groove for flexor hallucis longus.

Vascular supply

The calcaneus receives its arterial supply from the medial and lateral calcaneal arteries (arising from the posterior tibial and fibular arteries, respectively), fibular artery, posterior calcaneal anastomosis (formed from the posterior tibial and fibular arteries), medial and lateral plantar arteries, artery of the tarsal sinus and tarsal canal, branches of the lateral tarsal artery and perforating fibular arteries.

Innervation

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

Ossification

The calcaneus is the only tarsal bone that always has two ossification centres (Fig. 84.7). In addition to the main ossification centre, there is a scale-like posterior apophysis that covers most of the posterior, and part of the plantar, surfaces. The main centre appears prenatally in the third month, whereas the posterior apophysis appears in the sixth year in females and the eighth in males, fusing in the 14th and 16th years, respectively.

An os calcaneus secondarius, an accessory bone rather than a secondary ossification centre, occurs in 2% of individuals. When present, it is located on the dorsal beak or anterior process of the calcaneus in an interval between the anteromedial aspect of the calcaneus, the proximal ends of the cuboid and navicular, and the head of the talus. Other rare accessory bones of the calcaneus include the calcaneus accessorius in the region of the fibular trochlea, the os sustentaculi on the posterior aspect of the sustentaculum, the os subcalcis on the plantar aspect of the calcaneus slightly posterior to the origin of the plantar aponeurosis, and the os aponeurosis plantaris, which lies within the plantar aponeurosis in close proximity to the medial process of the calcaneal tuberosity.

Muscle and ligament attachments

The navicular tuberosity is the main attachment of tibialis posterior and a groove lateral to it transmits part of the tendon distally to the cuneiforms and middle three metatarsal bases. The plantar calcaneonavicular ligament is attached to a slight projection lateral to the groove and adjacent to the proximal surface. The calcaneonavicular part of the bifurcate ligament is attached to the rough part of the lateral surface (Fig. 84.5B).

Vascular supply

The dorsal aspect of the navicular is supplied either from a branch of, or directly from, the dorsalis pedis artery. Its plantar aspect is supplied from the medial plantar artery, and the tuberosity is supplied by an anastomosis from the dorsalis pedis and medial plantar arteries.

Innervation

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

Ossification

The navicular ossification centre appears during the third year (Fig. 84.7). It is sometimes affected by avascular necrosis between the ages of 4 and 7 years (Köhler’s disease). An accessory navicular bone, which is considered an anatomic variant, occurs in approximately 5% of individuals. It arises from a separate ossification centre in the region of the navicular tuberosity. There are three distinct types of accessory navicular. Type I is probably a sesamoid bone within the plantar aspect of the tendon of tibialis posterior at the level of the inferior calcaneonavicular ligament. In type II, the accessory bone is separated from the body of the navicular by a synchondrosis. Type III is commonly called ‘the cornuate navicular,’ where the accessory bone is united to the navicular by a bony ridge, and may represent the possible end stage of type II. An accessory navicular may be the source of pain in athletes. Type II is the most commonly symptomatic variant: it has been suggested that the pull of the tendon of tibialis posterior, the degree of foot pronation, and the location of the accessory bone in relation to the undersurface of the navicular may produce tension, shear, and/or compression forces on the synchondrosis.

Rarely, the navicular is bipartite and it arises from two distinct centres of ossification. This can lead to premature degeneration within the talocalcaneonavicular joint (Muller–Weiss disease). Occasionally, a small bone is found within the talocalcaneonavicular joint on its dorsal aspect. Referred to as an os talonaviculare dorsale, it represents either a separate accessory bone or a fractured osteophyte of the proximal dorsal aspect of the navicular.

Muscle (and ligament) attachments

The dorsal calcaneo-cuboid, cubonavicular, cuneocuboid and cubometatarsal ligaments are attached to the dorsal surface. Deep fibres of the long plantar ligament are attached to the proximal edge of the plantar ridge. Slips from the tendons of tibialis posterior and flexor hallucis brevis are attached to the projecting proximomedial part of the plantar surface. Interosseous, cuneocuboid and cubonavicular ligaments are attached to the rough part of the medial cuboidal surface. Proximally, the medial calcaneocuboid ligament, which is the lateral limb of the bifurcate ligament, is also attached to this surface.

Vascular supply

The cuboid is supplied by deep branches of the medial and lateral plantar arteries and by branches from the dorsal arterial network.

Innervation

The cuboid is innervated by branches from the lateral plantar, sural and deep fibular nerves.

Ossification

The cuboid frequently begins to ossify before birth, the primary ossification centre appearing just before birth (Fig. 84.7). An os cuboides secundarium is a rare accessory bone situated on the plantar aspect of the cuboid.

Muscle attachments

The plantar surface receives a slip from the tendon of tibialis posterior, in addition to part of the insertion of the tendon of fibularis longus. The medial surface receives the attachment of most of the tendon of tibialis anterior.

Vascular supply

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

Innervation

The medial cuneiform is supplied by the deep fibular and medial plantar nerves.

Ossification

The medial cuneiform may have two separate ossification centres, which appear during the second year of life (Fig. 84.7). Very rarely, the medial cuneiform is bipartite and there is a horizontal cleavage plane between the two moieties.

The os cuneo-1 metatarsale-I plantare is a rare accessory bone that occurs on the plantar aspect of the foot at the base of the first metatarsal and articulates with the plantar base of the first metatarsal and the medial cuneiform.

Muscle attachments

Part of the tendon of tibialis posterior is attached to the intermediate cuneiform.

Vascular supply

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

Innervation

The intermediate cuneiform is innervated by the deep fibular and medial plantar nerves.

Ossification

The ossification centre appears during the third year of life (Fig. 84.7). The os cuneo-2 metatarsale-II dorsale, a rare accessory bone, lies on the dorsal aspect of the joint between the intermediate cuneiform and the second metatarsal. It is wedge-shaped with its base orientated dorsally.

Muscle attachments

The plantar surface of the lateral cuneiform receives a slip from the tendon of tibialis posterior and, occasionally, part of flexor hallucis brevis.

Vascular supply

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

Innervation

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

Ossification

The lateral cuneiform ossifies during the first year of life (Fig. 84.7).

Muscle attachments

The first metatarsal receives attachments from the tendon of tibialis anterior medially, and the tendon of fibularis longus on its plantar aspect. It gives origin to the medial head of the first dorsal interosseus on the proximal aspect of the lateral surface.

Vascular supply

The first metatarsal is supplied by the first dorsal and first plantar metatarsal arteries and a superficial branch of the medial plantar artery, which together form a periosteal network. A nutrient artery enters the lateral surface of the mid-diaphysis. The head receives a medial, lateral and plantar supply from these arteries.

Innervation

The first metatarsal is innervated by the deep fibular and medial plantar nerves.

Ossification

The first metatarsal has two centres of ossification, one in the shaft, the other in the base (unlike the other metatarsals, in which the secondary ossification centre is distal). They appear during the tenth week of prenatal life and the third year of life, respectively (Fig. 84.7) and fuse between the 17th and 20th years. There may be a third centre in the first metatarsal head.

Muscle attachments

The lateral head of the first dorsal interosseous and the medial head of the second, are attached to the medial and lateral surfaces of the shaft, respectively.

Vascular supply

The blood supply of the second, third and fourth metatarsals follows the same pattern as that described for the first metatarsal, i.e. the bones are all supplied by branches of the dorsal and plantar metatarsal arteries. The nutrient artery enters the diaphysis on its lateral side near the metatarsal base. A constant plantar vessel supplies the head.

Innervation

The second metatarsal is innervated by branches of the deep fibular and branches of medial plantar nerve.

Ossification

There are two centres of ossification, one in the shaft and one distally in the metatarsal head (Fig. 84.7). Ossification of the shaft starts during the ninth prenatal week and ossification of the metatarsal head starts between the third and fourth years; fusion occurs between the 17th and 20th years.

Muscle attachments

The lateral head of the second dorsal interosseous and first plantar are attached to the medial surface of the shaft. The medial head of the third dorsal interosseous is attached to its lateral surface.

Vascular supply

The blood supply of the third metatarsal is the same as that of the second metatarsal, described above.

Innervation

The third metatarsal is innervated by the deep fibular and lateral plantar nerves.

Ossification

There are two centres of ossification, one in the shaft and one distally in the metatarsal head (Fig. 84.7). Ossification of the shaft starts during the ninth prenatal week and ossification of the metatarsal head starts between the third and fourth years; fusion occurs between the 17th and 20th years.

Muscle attachments

The lateral head of the third dorsal and second plantar interossei are attached to the medial surface. The medial head of the fourth dorsal interosseous is attached to the lateral surface.

Vascular supply

The blood supply of the fourth metatarsal is the same as that of the second and third metatarsals, described above.

Innervation

The fourth metatarsal is innervated by the deep fibular and lateral plantar nerves.

Ossification

There are two centres of ossification, one in the shaft and one distally in the metatarsal head (Fig. 84.7). Ossification of the shaft starts during the ninth prenatal week and ossification of the metatarsal head commences between the third and fourth years; fusion occurs between the 17th and 20th years.

Muscle attachments

The tendon of fibularis tertius is attached to the medial part of the dorsal surface and medial border of the shaft, and that of fibularis brevis 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. It is this attachment, and not that of fibularis brevis, which is responsible for avulsion fractures of the tuberosity. The plantar surface of the base is grooved by the tendon of abductor digiti minimi, and flexor digiti minimi brevis is attached here. The lateral head of the fourth dorsal and the third plantar interossei are attached to the medial side of the shaft.

Vascular supply

The fifth metatarsal is supplied by dorsal and plantar metatarsal arteries and an inconstant fibular marginal artery. The nutrient artery enters the diaphysis proximally and medially.

Innervation

The fifth metatarsal is innervated by branches from the sural, superficial fibular and lateral plantar nerves.

Ossification

There are three centres of ossification, one at the base in the region of the tuberosity (an apophysis), one in the shaft and one distally in the metatarsal head. Ossification of the shaft starts during the tenth prenatal week and ossification of the metatarsal head starts between the third and fourth years (Fig. 84.7). Fusion of the distal and shaft centres occurs between the 17th and 20th years, the proximal apophysis fuses earlier. An os vesalianum is a rare variant that should not be confused with the basal apophysis. (Fig. 84.12)

Fig. 84.12 Sites of sesamoid and accessory bones found in the left foot. A, Medial aspect; B, lateral aspect; C, plantar aspect.

Muscle attachments

Tendons of the long digital flexors and extensors are attached to the plantar and dorsal aspects of the bases of the distal phalanges of the lateral four toes. Flexor hallucis longus and extensor hallucis longus are similarly attached to the hallux. The bases of the middle phalanges receive the tendons of flexor digitorum brevis and extensor digitorum brevis. The proximal phalanges of the second, third, fourth and fifth toes each receive a lumbrical on their medial side; those of the second, third and fourth toes also receive an interosseous muscle on both sides. For further details of muscular, capsular and ligamentous arrangements in the toes refer to Fig. 84.5A,B. The terminal phalanx of the hallux normally shows a small degree of valgus (lateral) deviation, as may the proximal phalanx. This is presumed to be unrelated to footwear, because this degree of. deviation has also been observed in fetal specimens.

Vascular supply

The proximal phalanges receive most of their blood supply from the dorsal digital arteries. The middle phalanges are supplied by plantar and dorsal digital arteries. The distal phalanges receive their supply mainly from plantar digital arteries.

Innervation

The phalanges are innervated by the plantar and dorsal digital nerves.

Ossification

Phalanges are ossified from a primary centre for the shaft and a basal epiphysis (Fig. 84.7). Primary centres for the distal phalanges appear between the ninth and twelfth prenatal weeks, somewhat later in the fifth digit. Primary centres for the proximal phalanges appear between the 11th and 15th weeks, and later for intermediate phalanges, but there is wide variation. Basal centres appear between the second and eighth years (usually second or third in the hallux), and union with the shaft occurs by the 18th year. There is considerable variation in ossification and fusion dates.

Muscle attachments

The medial sesamoid receives an attachment from abductor hallucis, which provides a medial stabilizing influence on the sesamoid complex. The lateral sesamoid receives some fibres from the tendon of adductor hallucis, and this provides lateral stabilization. The medial and lateral sesamoids are connected by the intersesamoid ligament, which forms the floor of the tendinous canal for the tendon of flexor hallucis longus.

Vascular supply

There are three patterns of blood supply to the sesamoid bones. In 50% of cases the arterial supply is derived from the medial plantar artery and the plantar arch, in 25% of cases it is predominantly from the plantar arch and in 25% of cases it is from the medial plantar artery alone. The major arterial blood supply to the sesamoids enters from the proximal and plantar aspects, and only a minor contribution enters through the distal pole. The pattern of vascular supply determines the vulnerability of a sesamoid to avascular necrosis after injury to the bone.

Innervation

The medial and lateral sesamoids are innervated by the plantar digital nerves.

Ossification

The ossification centres of the sesamoids can be multiple or single.

Articulating surfaces

Articular surfaces are covered by hyaline cartilage. The talar trochlear surface, which is convex parasagittally and gently concave transversely, is wider in front; the distal tibial articular surface is reciprocally curved. The talar articular surface for the medial malleolus is a proximal area on the medial talar surface, and is fairly flat, comma-shaped and deeper anteriorly. The larger lateral talar articular surface is triangular and vertically concave, while the articular surface on the lateral malleolus is reciprocally curved. Posteriorly, the edge between the trochlear and fibular articular surfaces of the talus is bevelled to a narrow, flat triangular area that articulates with the inferior transverse tibiofibular ligament (Fig. 84.13A); all surfaces are contiguous. The bones are held together by a fibrous capsule, and by medial (deltoid), anterior and posterior talofibular and calcaneofibular ligaments.

Fig. 84.13 The left ankle and tarsal joints. A, Posterior aspect. B, Medial aspect. C. Lateral aspect.

Fibrous capsule

Around the joint, the fibrous capsule is thin in front and behind. It is attached proximally to the borders of the tibial and malleolar articular surfaces, and distally to the talus near the margins of its trochlear surface, except in front where it reaches the dorsum of the talar neck. The capsule is strengthened by strong collateral ligaments. Its posterior part consists mainly of transverse fibres. It blends with the inferior transverse ligament and is thickened laterally where it reaches the fibular malleolar fossa.

Ligaments

The ligaments of the talocrural joint are the medial and lateral collateral ligaments.

Synovial membrane

The joint is lined by synovial membrane which projects into the inferior (distal) tibiofibular joint.

Vascular supply and lymphatic drainage

The talocrural joint is supplied by malleolar branches of the anterior and posterior tibial and fibular arteries. Lymphatic drainage is via vessels accompanying the arteries and via the long and short saphenous veins superficially.

Innervation

The talocrural joint is innervated by branches from the deep fibular, saphenous, sural and tibial nerves (or medial and lateral plantar nerves, depending on the level of division of the tibial nerve). Occasionally, the superficial fibular nerve also supplies the ankle joint.

For a comprehensive account of the innervation of the ankle joint (and other foot joints) see Gardner & Gray (1968).

Relations

Anteriorly, from medial to lateral, are tibialis anterior, extensor hallucis longus, the anterior tibial vessels, deep fibular nerve, extensor digitorum longus and fibularis tertius; posteromedially from medial to lateral, are tibialis posterior, flexor digitorum longus, the posterior tibial vessels, tibial nerve, flexor hallucis longus; in the groove behind the lateral malleolus are the tendons of fibularis longus and brevis. The tendon of fibularis brevis lies anterior to the tendon of fibularis longus at this level (Fig. 84.14). The long saphenous vein and saphenous nerve cross the ankle joint medial to the tendon of tibialis anterior and anterior to the medial malleolus, the nerve lying posterior to the vein.

All of the above structures are at risk during surgery on the ankle: the main structures at risk are the neurovascular structures anteriorly and posteromedially. Branches of the superficial fibular nerve are at risk on the anterolateral aspect of the ankle, particularly during ankle arthroscopy.

Factors maintaining stability

Passive stability is conferred upon the ankle mainly by the medial and lateral ligament complexes, the distal tibiofibular ligaments, the tendons crossing the joint, the bony contours and the capsular attachments. Dynamic stability is conferred by gravity, muscle action and ground reaction forces. Stability requires the continuous action of soleus assisted by gastrocnemius: it increases when leaning forward, and decreases when leaning backwards. If backward sway takes the projection of the centre of gravity (‘weight line’) posterior to the transverse axes of the ankle joints, the plantar flexors relax and the dorsiflexors contract.

Failure of the fibular muscles can lead progressively to varus instability, whereas long-standing failure of the tendon of tibialis posterior, which is relatively common in the elderly female, can result in valgus instability of the ankle and particularly a planovalgus foot deformity.

Muscles producing movement

Dorsiflexion is produced by tibialis anterior, assisted by extensors digitorum longus and hallucis longus, and fibularis tertius. Plantar flexion is produced by gastrocnemius and soleus, assisted by plantaris, tibialis posterior, flexors hallucis longus and digitorum longus.

Articulating surfaces

The distal tibiofibular joint is between the rough, medial convex surface on the distal end of the fibula and the rough concave surface of the fibular notch of the tibia. These surfaces are separated distally for approximately 4 mm by a synovial prolongation from the ankle joint, and may be covered by articular cartilage in their lowest parts.

Fibrous capsule

The distal tibiofibular joint does not have a capsule.

Ligaments

The ligaments of the inferior (distal) tibiofibular joint are the anterior, interosseous and posterior ligaments.

Synovial membrane

The synovial membrane of the ankle joint projects into the distal 4 mm or so of the inferior tibiofibular joint.

Vascular supply and lymphatic drainage

The inferior tibiofibular joint is supplied by the perforating branch of the fibular artery and the medial malleolar branches of the anterior and posterior tibial arteries. Lymphatic drainage is via vessels corresponding to the arteries, and via vessels that accompany the long and short saphenous veins.

Innervation

The inferior tibiofibular joint is innervated by branches from the deep fibular and sural nerves.

Relations

No significant structures pass anterior to the anterior aspect of the inferior tibiofibular joint, but the superficial fibular nerve is at risk during surgery to this area. Posteriorly, the fibular artery passes over the posterior tibiofibular ligament and is at risk in the posterolateral approach to the fibula.

Factors maintaining stability

Stability is maintained in part by the bone contours, but mainly by the dense anterior and posterior tibiofibular and the interosseous ligaments.

Muscles producing movement

No muscles act on the inferior tibiofibular joint, which moves only slightly. Because of the varying slope of the lateral surface of the body of talus, the fibula undergoes a small degree of lateral rotation during dorsiflexion at the ankle, and this results in slight widening of the interval between the bones. Testing for a significant disruption of this joint is usually carried out with the patient under anaesthetic and involves applying an external rotation and abduction force, looking for abnormal widening of the syndesmosis. Excessive anterior/posterior glide of the fibula relative to the tibia also indicates a disruption of the joint.

Articulating surfaces

The subtalar joint proper involves the concave posterior calcaneal facet on the posterior part of the inferior surface of the talus and the convex posterior facet on the superior surface of the calcaneus (Fig. 84.15A,B).

Fibrous capsule

The fibrous capsule envelops the joint, its fibres are short and attached to its articular margins.

Ligaments

The ligaments of the talocalcaneal joint are the lateral, medial and interosseous talocalcaneal ligaments and the cervical ligament.

Synovial membrane

The synovial cavity of the talocalcaneal joint is usually quite separate and does not communicate with those of other tarsal joints. However, direct communication with the ankle joint has been observed in rare instances.

Innervation

The talocalcaneal joint is innervated by branches of the posterior tibial, medial plantar and sural nerves.

Relations

Posteromedially, in the region of the posterior aspect of the talocalcaneal joint, and viewed from anterior to posterior, lie the veins on either side of the posterior tibial artery, the tibial nerve and the tendon of flexor hallucis longus. These neurovascular structures are at risk in posteromedial approaches to the ankle and talocalcaneal joints. On the lateral side, the tendon of fibularis brevis lies anterior to the tendon of fibularis longus, both passing behind the fibular malleolus in proximity to the talocalcaneal joint. The sural nerve lies just posterior to the fibular tendons and is at risk during lateral exposure of the joint.

Factors maintaining stability

Stability is conferred by the bony contours of the hindfoot plus the above mentioned ligaments; it is not known which ligaments provide the most stability. An additional ligamentous restraint is provided by the calcaneofibular component of the lateral ligament complex. The tendons crossing the articulation also aid stability.

Muscles producing movement

Heel inversion is controlled by tibialis anterior, tibialis posterior and the gastrocnemius–soleus complex via the calcaneal tendon; the long flexors of the toes also contribute. Heel eversion results from the pull of fibularis longus, brevis and tertius in addition to the long extensors of the toes.

Articulating surfaces

The ovoid talar head is continuous with the triple-faceted anterior area of its inferior surface. The whole fits the concavity formed collectively by the posterior surface of the navicular, the middle and anterior talar facets of the calcaneus, and the superior fibrocartilaginous surface of the plantar calcaneonavicular ligament (spring ligament). The bones are connected by a fibrous capsule and by the talonavicular and plantar calcaneonavicular ligaments, and the calcaneonavicular part of the bifurcate ligament.

Fibrous capsule

The fibrous capsule is poorly developed, except posteriorly, where it is thick and blends with the anterior part of the interosseous ligament filling the tarsal sinus.

Ligaments

The ligaments of the talocalcaneonavicular joint are the talonavicular and plantar calcaneonavicular (spring) ligaments.

Plantar calcaneonavicular (spring) ligament

The plantar calcaneonavicular (spring) ligament is a broad, thick band connecting the anterior margin of the sustentaculum tali to the plantar surface of the navicular (Figs 84.13B; 84.15A; 84.17). It ties the calcaneus to the navicular below the head of the talus as part of its articular cavity and it sustains the medial longitudinal arch of the foot. The dorsal surface of the ligament has a triangular fibrocartilaginous facet on which part of the talar head rests (Fig. 84.15A). Its plantar surface is supported medially by the tendon of tibialis posterior and laterally by the tendons of flexors hallucis longus and digitorum longus; its medial border is blended with the anterior superficial fibres of the medial (deltoid) ligament. The calcaneonavicular ligament is described below as the medial band of the bifurcate ligament.

Fig. 84.17 Ligaments on the plantar aspect of the foot.

(From Sobotta 2006.)

Synovial membrane

The talocalcaneonavicular joint is a synovial joint whose cavity sometimes communicates with that of the talocalcaneal joint.

Innervation

The talocalcaneonavicular joint is innervated by the deep fibular and medial plantar nerves.

Relations

On the medial side from dorsal to plantar lie the tendon of tibialis posterior and the tendon of flexor digitorum longus above the sustentaculum tali, and the flexor hallucis longus tendon below. At this point, flexor hallucis longus lies deep to the medial and lateral plantar branches of the posterior tibial artery and nerve. The latter structures are at risk during medial approaches to the joint, e.g. resection of talocalcaneal coalition. Dorsally from medial to lateral lie the tendons of tibialis anterior and extensor hallucis longus, the deep fibular nerve and the dorsalis pedis artery, the muscle belly of extensor hallucis brevis passing medially and deep to the tendons of extensor digitorum longus and fibularis tertius. Structures at risk during the dorsal approach to the talonavicular joint include the branches of the superficial fibular nerve superficially and the dorsalis pedis artery and deep fibular nerve deep to the inferior extensor retinaculum.

Factors maintaining stability

Stability of the joint is due to a combination of factors: bony contours, the strong plantar calcaneonavicular (spring) ligament, and the calcaneonavicular component of the bifurcate ligament.

Muscles producing movement

The muscles producing movement are as described above for the talocalcaneal joint.

Articulating surfaces

The articular surfaces of the calcaneocuboid joint, which is 2 cm proximal to the tubercle on the fifth metatarsal base, are between the anterior (distal) surface of the calcaneus and the posterior (proximal) surface of the cuboid.

Fibrous capsule

The fibrous capsule is thickened dorsally as the dorsal calcaneocuboid ligament. The synovial cavity of this joint is separate, and does not communicate with those of other tarsal articulations (Fig. 84.6).

Ligaments

The ligaments of the calcaneocuboid joint are the bifurcate, long plantar and plantar calcaneocuboid ligaments.

Synovial membrane

A synovial membrane lines the calcaneo-cuboid joint.

Innervation

The calcaneocuboid joint is innervated on its plantar aspect by the lateral plantar nerve, and dorsally by the sural and deep fibular nerves.

Relations

Fibularis longus and abductor digiti minimi pass in proximity to the joint, and the lateral plantar nerve passes medially. Extensor digitorum brevis overlies the lateral aspect of the joint. The sural nerve and the tendon of fibularis longus are at risk during approaches to an os peroneum.

Factors maintaining stability

The calcaneocuboid joint only permits a small amount of movement; its stability reflects the bony contours and strong ligaments described above.

Muscles producing movement

Gliding occurs between the calcaneus and cuboid, with conjunct rotation upon each other during inversion and eversion of the entire foot. The movements are brought about by the same muscles that act on the talocalcaneal and talocalcaneonavicular joints.

Articulating surfaces

The navicular articulates distally with the cuneiform bones where the distal navicular surface is transversely convex and divided into three facets by low ridges that are adapted to the proximal, slightly curved surfaces of the cuneiforms.

Fibrous capsule

The fibrous capsule is continuous with those of the intercuneiform and cuneocuboid joints and it is also connected to the second and third cuneometatarsal joints and intermetatarsal joints between the second to fourth metatarsal bones.

Ligaments

The ligaments of the naviculocuneiform joint are the dorsal and plantar ligaments.

Synovial membrane

The synovial membrane lines the fibrous capsule in the manner outlined above.

Innervation

The naviculocuneiform joint is innervated dorsally by branches from the deep fibular nerve. The medial and intermediate naviculocuneiform joints receive a plantar innervation from the medial plantar nerve, and the lateral naviculocuneiform joint is innervated from the lateral plantar nerve.

Relations

The tendon of tibialis posterior sends fibres to the medial cuneiform and crosses the joint on its medial side; it is vulnerable to injury when a medial surgical approach is used, as are the dorsal venous arch and the saphenous nerve. The tendon of tibialis anterior passes over the dorsomedial aspect of the joint and the tendon of extensor hallucis longus is lateral. Running over the intermediate cuneiform, from medial to lateral, are the deep fibular nerve, the dorsalis pedis artery and the muscle belly of extensor hallucis brevis, all of which are vulnerable during dorsal exposure of the joint. On the lateral aspect of the joint, the superficial structures at risk are the superficial fibular nerve and the dorsal venous arch.

Muscles producing movement

Movements at the naviculo-cuneiform, cuboideonavicular, intercuneiform and cuneocuboid joints are slight and subtle gliding and rotational movements that occur during pronation or supination of the foot: when alterations occur in a loaded foot in contact with the ground, they increase suppleness when the forefoot is stressed, e.g. in the initial thrust of running and jumping. The muscles responsible for these slight movements are tibialis anterior, tibialis posterior, fibularis longus and brevis and the long flexors and extensors of the toes.

Ligaments

The ligaments of the intercuneiform and cuneocuboid joints are the dorsal, plantar and interosseous ligaments.

Innervation

The intercuneiform and cuneocuboid joints are innervated dorsally via the deep fibular nerve. The plantar aspect of the medial two joints is innervated from the medial plantar nerve, and the plantar aspect of the lateral joints is innervated from the lateral plantar nerve.

Muscles producing movement

The muscles producing movement are as described above for the naviculocuneiform joint.

Articulating surfaces

The first metatarsal articulates with the medial cuneiform; the second is recessed between the medial and lateral cuneiforms and articulates with the intermediate cuneiform; the third articulates with the lateral cuneiform; the fourth articulates with the lateral cuneiform and the cuboid; the fifth articulates with the cuboid. The joints are approximately on a line from the tubercle of the fifth metatarsal to the tarsometatarsal joint of the hallux, except for that between the second metatarsal and intermediate cuneiform, which is 2–3 mm proximal (Figs 84.5A; 84.11).

Fibrous capsule

The hallucal joint has its own capsule. The articular capsules and cavities of the second and third are continuous with those of the intercuneiform and naviculocuneiform joints, but are separated from the fourth and fifth joints by an interosseous ligament between the lateral cuneiform and fourth metatarsal base.

Ligaments

The bones are connected by dorsal and plantar tarsometatarsal and interosseous cuneometatarsal ligaments.

Synovial membrane

The first tarsometatarsal joint has its own capsule, with a synovial lining. The other joints are similarly arranged, but there is a communication between the second and third and between the fourth and fifth tarsometatarsal joints.

Innervation

The interosseous cuneometatarsal ligaments are innervated dorsally via the deep fibular nerve. The plantar aspects of the medial two joints are innervated from the medial plantar nerve, and the plantar aspects of the lateral joints are innervated by the lateral plantar nerve.

Relations

From medial to lateral, the following structures cross the dorsal aspect of the tarsometatarsal joints: the saphenous nerve, the dorsal venous arch, the tendon of extensor hallucis longus, the dorsalis pedis artery, the deep fibular nerve, extensor hallucis brevis, the tendons of extensor digitorum longus, extensor digitorum brevis, fibularis tertius and fibularis brevis. Branches of the superficial fibular nerve are variable in location on the dorsum. The sural nerve lies just inferior to the tendon of fibularis brevis in the subcutaneous tissues. Surgery involving the tarsometatarsal joints is performed through a dorsal approach, and therefore all of these structures are potentially at risk.

Factors maintaining stability

The major stabilizers of the tarsometatarsal joints are the associated ligaments. However, despite the strength of the ligaments, this joint complex is vulnerable to injury because of the lack of ligamentous connection between the first and second metatarsal bases. The medial interosseous ligament or Lisfranc’s ligament is responsible for the tell-tale avulsion fracture of the second metatarsal base, which may be the only radiographic indication of abnormality after injury to this part of the foot. It is a highly significant injury that is often missed: failure to recognize and treat this injury by surgical reduction and fixation can lead to long-term disability.

Muscles producing movement

Movements between the tarsal and metatarsal bones are limited to flexion and extension, except in the first tarsometatarsal joint, where some abduction and rotation also occur. The muscles that produce this motion are tibialis anterior and fibularis longus. Flexion and extension are brought about by the long and short flexors and extensors of the toes. Movement between the medial cuneiform and first metatarsal, and between the fourth and fifth metatarsal bases and the cuboid, is moderate and allows the foot to adapt to uneven surfaces, whereas movement between the second and third metatarsal bases and their corresponding cuneiforms is very limited.

Ligaments

The ligaments of the intermetatarsal joints include the dorsal and plantar intermetatarsal ligaments.

Articulating surfaces

Articular surfaces cover the distal and plantar, but not the dorsal, aspects of the metatarsal heads. The plantar aspect of the first metatarsal head has two longitudinal grooves separated by a ridge (the crista). Each articulates with a sesamoid bone embedded in the capsule of the joint, formed here by the two tendons of flexor hallucis brevis. The sesamoids are connected to each other by the intersesamoid ligament, which forms the floor of the tendinous canal for the tendon of flexor hallucis longus. The medial sesamoid receives an attachment from abductor hallucis and the lateral sesamoid receives an attachment from adductor hallucis.

Articular areas on the proximal phalangeal bases are concave. The ligaments are capsular, plantar, deep transverse metatarsal and collateral.

Fibrous capsules

Fibrous capsules are attached to their articular margins. They are thin dorsally, and may be separated from the long extensor tendons by small bursae, or they may be replaced by the tendons, but they are inseparable from the plantar and collateral ligaments. The plantar aponeurosis blends with the plantar capsule to form the so-called ‘plantar plate’ which inserts distally into the base of the proximal phalanx via medial and lateral bundles. Proximally, the plate is attached to the metatarsal head via a thin synovial fold. It also receives an attachment from the accessory collateral ligament.

Ligaments

The ligaments of the metatarsophalangeal joints are the plantar, deep transverse metatarsal and collateral ligaments.

Synovial membrane

Each metatarsophalangeal joint is a separate synovial joint.

Innervation

The main nerve supply of the metatarsophalangeal joints is from the plantar interdigital nerves, which supply the first, second, third and medial half of the fourth metatarsophalangeal joint on their plantar aspects. Digital branches of the lateral plantar nerve supply the lateral half of the fourth joint, and both medial and lateral aspects of the fifth joint, on their plantar sides. The dorsomedial side of the hallucal metatarsophalangeal joint is supplied by the medial dorsal cutaneous branch of the superficial fibular nerve. The deep fibular nerve supplies the dorsolateral side of the hallucal metatarsophalangeal joint and the medial side of the metatarsophalangeal joint of the second toe.

Relations

Dorsally, the tendon of extensor hallucis longus lies medial to the tendon of extensor hallucis brevis. The same arrangement occurs in the lesser toes with the tendons of extensor digitorum longus and brevis. The interossei are plantarmedial and plantarlateral, dorsal to the intermetatarsal ligament, whereas the lumbrical tendons and the digital artery and nerve are plantar to the intermetatarsal ligament. The long and short flexors lie on the plantar aspect of the joint in the midline. If approaching the metatarsophalangeal joint surgically from the plantar surface, it is important not to stray from the midline.

Factors maintaining stability

The first metatarsophalangeal joint owes its stability to its capsuloligamentous structures, and to flexor and extensor hallucis brevis, with a small contribution from flexor and extensor hallucis longus or the bony contours. The metatarsophalangeal joints of the lesser toe are stabilized principally by the collateral ligaments and plantar plates. Rupture of the plantar plate leads to hammer toe deformity.

Muscles producing movement

The types of movements that occur at these joints are like those that occur at the corresponding joints in the hand, but the range of movement is quite different. In contrast to the metacarpophalangeal joints, the range of active extension that can occur at the metatarsophalangeal joints (50–60°) is greater than that of flexion (30–40°): this is an adaptation to the needs of walking, and is most marked in the hallucal joint, where flexion is a few degrees while extension may reach 90°. When the foot is on the ground, metatarsophalangeal joints are already extended to at least 25° because the metatarsals incline proximally in the longitudinal arches of the foot (Fig. 84.8A). The range of passive movements in these joints is 90° (extension) and 45° (flexion), according to Kapandji (1974). The following muscles produce movements at the metatarsophalangeal joints:

Hallux valgus

Hallux valgus is a common condition, occurring mainly in individuals who have a genetic predisposition. Footwear is implicated in the condition, which presumably accounts for the greater incidence in females. Metatarsus primus varus, an adduction deformity of the first metatarsal, is commonly associated with hallux valgus.

The more spheroidal the shape of the first metatarsal head, the more likely it is to be unstable. Conversely, a flat metatarsal head is less likely to be associated with hallux valgus. No muscle inserts into the first metatarsal head, and therefore its position is determined by the position of the proximal phalanx. As the proximal phalanx moves laterally on the metatarsal head, it pushes the head medially. This leads to attenuation of the medial soft tissue structures and contracture of the lateral ones. The sesamoid sling, which is anchored laterally by adductor hallucis, remains in place as the head moves medially, displacing the sesamoids from beneath the metatarsal head. As this happens, the weakest point of the medial capsule fails, so that abductor hallucis slips under the metatarsal head. This leads to failure of the intrinsic muscles to stabilize the joint, and the pull of abductor hallucis leads to spinning of the proximal phalanx, which results in a pronation deformity. Failure to intervene surgically inevitably results in a progressive deformity.

Innervation

The interphalangeal articulations are innervated by branches from the plantar interdigital nerves. The medial dorsal cutaneous branch of the superficial fibular nerve also supplies the hallucal interphalangeal joint. Branches of the deep fibular, intermediate dorsal cutaneous and sural nerves sometimes supply the joints of the lesser toes.

Muscles producing movement

Movements are flexion and extension, which are greater in amplitude between the proximal and middle phalanges than between the middle and distal. Flexion is marked, but extension is limited by tension of the flexor muscles and plantar ligaments. Abduction, adduction and rotation occur to a minor extent.

Vascular supply

The blood supply to the calcaneal tendon is poor: the predominant artery is a recurrent branch of the posterior tibial artery which mainly supplies peritendinous tissues (Taylor & Razaboni 1994). There is an additional supply proximally from intramuscular arterial branches and distally from the calcaneus. The vascularity of the mid-substance of the tendon is relatively poor, although some blood enters the tendon at this point through its anterior surface. During surgery, the paratenon is therefore best left intact in this region.

The calcaneal tendon is not the only plantar flexor of the ankle, which is one of the reasons ruptures of the calcaneal tendon may not always be clinically apparent. However, it is a frequent site of pathology because of its susceptibility to rupture, degenerative change (tendinosis) and inflammation (paratendonitis): the area of relative avascularity in the mid-substance of the tendon is where the majority of problems occur.

Relations

The calcaneal tendon is subcutaneous. The sural nerve crosses its lateral border about 10 cm above its insertion: the nerve is especially vulnerable here to iatrogenic injury during surgery. Distally, there are bursae superficial and deep to the tendon. The muscle belly of flexor hallucis longus lies deep to the deep fascia on the anterior surface of the tendon.

Action

Plantar flexion of the ankle joint. The tendon fibres spiral laterally through 90° as they descend, so that the fibres associated with gastrocnemius come to insert on the bone more laterally, and those associated with soleus more medially.

Heel bursae

There are three locations about the heel where bursae occur. The most common is the retrocalcaneal bursa, which lies between the calcaneal tendon and the posterior surface of the calcaneus. An almost constant finding, it has an anterior bursal wall composed of fibrocartilage and a thin posterior wall which blends with the thin epitenon (epitendineum) of the calcaneal tendon. Dorsiflexion of the ankle results in compression of the bursa. Less common are an adventitious bursa superficial to the calcaneal tendon, and a subcalcaneal bursa between the inferior surface of the calcaneus and the origin of the plantar aponeurosis. A prominent superolateral calcaneal tuberosity may impinge on the deep aspect of the calcaneal tendon where it inserts onto the calcaneus (Haglund’s disease). It is often associated with a retrocalcaneal bursa, and symptoms are exacerbated by dorsiflexion of the ankle, because this movement increases the pressure within the bursa and causes impingement of calcaneus against the tendon insertion.

Attachments

Abductor hallucis arises principally from the flexor retinaculum, but also from the medial process of the calcaneal tuberosity, the plantar aponeurosis, and the intermuscular septum between this muscle and flexor digitorum brevis. The muscle fibres end in a tendon that is attached, together with the medial tendon of flexor hallucis brevis, to the medial side of the base of the proximal phalanx of the hallux. Some fibres are attached more proximally to the medial sesamoid bone of this toe. The muscle may also derive some fibres from the dermis along the medial border of the foot.

Relations

Abductor hallucis lies along the medial border of the foot and covers the origins of the plantar vessels and nerves (Fig. 84.20).

Fig. 84.20 Plantar nerves and vessels in relation to muscle layers.

(From Sobotta 2006.)

Vascular supply

Abductor hallucis is supplied by the medial malleolar network, medial calcaneal branches of the lateral plantar artery (Fig. 84.9), the medial plantar artery (directly and via superficial and deep branches), the first plantar metatarsal artery and perforators from the plantar arterial arch.

Innervation

Abductor hallucis is innervated by the medial plantar nerve, S1 and S2. Contraction of the muscle confirms an intact medial plantar nerve when the integrity of this nerve is in question.

Action

Abductor hallucis produces abduction of the hallux.

Testing

Abductor hallucis is tested clinically by instructing the subject to resist a forcibly applied lateral deviation of the proximal phalanx.

Clinical anatomy

The deep fascia has been implicated in chronic heel pain, because it can cause entrapment of the first branch of the lateral plantar nerve that lies immediately deep to it. The abductor hallucis fascia is strong and can be used in soft tissue augmentation following correction of hallux valgus. Rarely, persistent, exaggerated tonus in the muscle may be a cause of varus deformity of the foot, necessitating surgical intervention. An abductor hallucis flap is sometimes used for provision of soft tissue cover.

Attachments

Flexor digitorum brevis arises by a narrow tendon from the medial process of the calcaneal tuberosity, from the central part of the plantar aponeurosis, and from the intermuscular septa between it and adjacent muscles. It divides into four tendons, which pass to the lateral four toes; the tendons enter digital tendon sheaths accompanied by the tendons of flexor digitorum longus, which lie deep to them. At the bases of the proximal phalanges, each tendon divides around the corresponding tendon of flexor digitorum longus; the two slips then reunite and partially decussate, forming a tunnel through which the tendon of flexor digitorum longus passes to the distal phalanx. The short flexor tendon divides again and attaches to both sides of the shaft of the middle phalanx. The way in which the tendons of flexor digitorum brevis divide and attach to the phalanges is identical to that of the tendons of flexor digitorum superficialis in the hand. The slip to a given toe may be absent, or it may be replaced by a small muscular slip from the long flexor tendon or from flexor accessorius. Conversely, the slip may be joined by a second, supernumerary slip.

Relations

Flexor digitorum brevis lies immediately deep to the central part of the plantar aponeurosis (Fig. 84.19A). Its deep surface is separated from the lateral plantar vessels and nerves by a thin layer of fascia.

Vascular supply

Flexor digitorum brevis is supplied by the lateral and medial plantar arteries, the plantar metatarsal arteries and the plantar digital arteries to the lateral four toes.

Nerve supply

Flexor digitorum brevis is innervated by the medial plantar nerve, S1 and S2.

Actions

Flexor digitorum brevis flexes the lesser toes at the proximal interphalangeal joint, with equal effect in any position of the ankle joint.

Testing

To test the action of flexor digitorum brevis, the examiner passively extends the distal interphalangeal joint and asks the individual to flex the toes at the proximal interphalangeal joint. Contracture of the flexor tendon can lead to toe deformities, and release or lengthening procedures may be required. The muscle belly is sometimes excised as a flap to cover a soft tissue defect.

Attachments

Abductor digiti minimi arises from both processes of the calcaneal tuberosity, from the plantar surface of the bone between them, from the plantar aponeurosis and from the intermuscular septum between the muscle and flexor digitorum brevis. Its tendon glides in a smooth groove on the plantar surface of the base of the fifth metatarsal and is attached, with flexor digiti minimi brevis, to the lateral side of the base of the proximal phalanx of the fifth toe; hence it is more a flexor than an abductor. Some of the fibres arising from the lateral calcaneal process usually reach the tip of the tuberosity of the fifth metatarsal (Figs 84.8B; 84.11) and may form a separate muscle, abductor ossis metatarsi digiti quinti. An accessory slip from the base of the fifth metatarsal is not infrequent.

Relations

Abductor digiti minimi lies along the lateral border of the foot, and its medial margin is related to the lateral plantar vessels and nerve (Fig. 84.20).

Vascular supply

Abductor digiti minimi is supplied by the medial and lateral plantar arteries (Fig. 84.20; see Fig. 84.24A), the plantar digital artery to the lateral side of minimus, branches from the plantar arch, the fourth plantar metatarsal artery and end twigs of the arcuate and lateral tarsal arteries (Fig. 84.9).

Fig. 84.24 The plantar arteries of the left foot. A, Superficial dissection. B, Deep dissection.

Innervation

Abductor digiti minimi is innervated by the lateral plantar nerve, S1, S2 and S3.

Action

Despite its name, abductor digiti minimi is more a flexor than an abductor of the metatarsophalangeal joint of the little toe.

Attachments

Flexor digitorum accessorius (Fig. 84.19B), also known as quadratus plantae, arises by two heads, with the long plantar ligament situated deeply in the interval between the two heads. The medial head is larger and more fleshy and is attached to the medial concave surface of the calcaneus, below the groove for the tendon of flexor hallucis longus. The lateral head is flat and tendinous and is attached to the calcaneus distal to the lateral process of the tuberosity, and to the long plantar ligament. The muscle belly inserts into the tendon of flexor digitorum longus at the point where it is bound by a fibrous slip to the tendon of flexor hallucis longus and where it divides into its four tendons.

The muscle is sometimes absent altogether. Its distal attachment to the tendons of flexor digitorum longus may vary, which means that the fourth and fifth long flexor tendons may, at times, fail to receive slips from the accessorius.

Relations

The medial plantar nerve passes medial to and the lateral plantar nerve passes superficial to flexor accessorius.

Vascular supply

Flexor digitorum accessorius is supplied by the stem of the medial plantar artery (to the medial head), the lateral plantar artery and the plantar arch.

Innervation

Flexor digitorum accessorius is innervated by the lateral plantar nerve, S1, S2 and S3.

Action

By pulling on the tendons of flexor digitorum longus, flexor digitorum accessorius provides a means of flexing the lateral four toes in any position of the ankle joint.

Attachments

The lumbrical muscles are four small muscles (numbered from the medial side of the foot) which are accessory to the tendons of flexor digitorum longus (Fig. 84.19A,B). They arise from these tendons as far back as their angles of separation, each springing from the sides of two adjacent tendons, except for the first lumbrical, which arises only from the medial border of the first tendon. The muscles end in tendons that pass distally on the medial sides of the four lesser toes and are attached to the dorsal digital expansions on their proximal phalanges.

Relations

The lumbricals are intimately related to the tendons of flexor digitorum longus before the latter enter their corresponding fibrous flexor sheaths. The lumbricals remain outside the fibrous flexor sheaths and cross the plantar aspects of the deep transverse metatarsal ligaments before reaching the dorsal digital expansions.

Vascular supply

The lumbricals are supplied by the lateral plantar artery and plantar arch, and by four plantar metatarsal arteries (four distal perforating arteries joined by three proximal perforating arteries). Their tendons are supplied by twigs from the dorsal digital arteries (and their parent dorsal metatarsal arteries) to the lateral four toes.

Innervation

The first lumbrical is supplied by the medial plantar nerve, and the remainder are supplied by the deep branch of the lateral plantar nerve, S2 and S3.

Action

The lumbricals help to maintain extension of the interphalangeal joints of the toes. In injuries of the tibial nerve, and in conditions such as the hereditary motor–sensory neuropathies (e.g. Charcot–Marie–Tooth disease), lumbrical dysfunction contributes to clawing of the toes.

Attachments

Flexor hallucis brevis has a bifurcate tendon of origin (Figs 84.19A,B; 84.21). The lateral limb arises from the medial part of the plantar surface of the cuboid, posterior to the groove for the tendon of fibularis longus, and from the adjacent part of the lateral cuneiform. The medial limb has a deep attachment directly continuous with the lateral division of the tendon of tibialis posterior, and a more superficial attachment to the middle band of the medial intermuscular septum. The belly of the muscle divides into medial and lateral parts, the twin tendons of which are attached to the sides of the base of the proximal phalanx of the hallux. The medial part blends with the tendon of abductor hallucis, and the lateral with that of adductor hallucis, as they reach their terminations.

A sesamoid bone usually occurs in each tendon near its attachment. Clinical problems with flexor hallucis brevis are usually related to the associated sesamoid bones. However, excision of both sesamoids leads to disruption of both tendons and a subsequent extension deformity at the first metatarsophalangeal joint: such surgery is therefore not recommended.

Accessory slips may arise proximally from the calcaneus or long plantar ligament. A tendinous slip may extend to the proximal phalanx of the second toe.

Relations

Flexor hallucis brevis lies on the underside of the first metatarsal shaft; abductor hallucis lies medially. The medial digital nerve to the hallux and the tendon of flexor hallucis longus pass to the hallux on its plantar surface. The medial plantar nerve lies more superficially on its lateral side.

Vascular supply

Flexor hallucis brevis is supplied by branches of the medial plantar artery, the first plantar metatarsal artery, the lateral plantar artery and the plantar arch.

Innervation

Flexor hallucis brevis is supplied by the medial plantar nerve, S1 and S2.

Action

Flexor hallucis brevis flexes the proximal phalanx of the hallux.

Testing

The individual is asked to flex the first metatarsophalangeal joint with the interphalangeal joint extended, thereby eliminating the action of flexor hallucis longus.

Attachments

Adductor hallucis arises by oblique and transverse heads (Figs 84.19B; 84.21). The oblique head springs from the bases of the second, third and fourth metatarsal bones, and from the fibrous sheath of the tendon of fibularis longus. The transverse head, a narrow, flat fasciculus, arises from the plantar metatarsophalangeal ligaments of the third, fourth and fifth toes (sometimes only from the third and fourth), and from the deep transverse metatarsal ligaments between them. The oblique head has medial and lateral parts. The medial part blends with the lateral part of flexor hallucis brevis and is attached to the lateral sesamoid bone of the hallux. The lateral part joins the transverse head and is also attached to the lateral sesamoid bone and directly to the base of the first phalanx of the hallux. There is no phalangeal attachment for the transverse part of the muscle; fibres that fail to reach the lateral sesamoid bone are attached with the oblique part.

The transverse part of adductor hallucis is sometimes absent; part of the muscle may be attached to the first metatarsal, constituting an opponens hallucis; a slip may also extend to the proximal phalanx of the second toe.

Relations

Adductor hallucis lies plantar to the metatarsal shafts and interossei and the long and short toe flexors. The medial and lateral plantar arteries and nerves are superficial, and flexor hallucis brevis is proximal and medial.

Vascular supply

Adductor hallucis is supplied by branches of the medial plantar artery, the lateral plantar artery, the plantar arch and the first to fourth plantar metatarsal arteries.

Innervation

Adductor hallucis is innervated by the deep branch of the lateral plantar nerve, S2 and S3.

Action

Adductor hallucis partly flexes the proximal phalanx of the hallux, but also stabilizes the metatarsal heads.

Clinical anatomy

Adductor hallucis is one of the deforming forces in hallux valgus and needs to be released during a distal soft tissue release when there is a fixed deformity.

Attachments

Flexor digiti minimi brevis arises from the medial part of the plantar surface of the base of the fifth metatarsal bone, and from the sheath of fibularis longus (Figs 84.19B; 84.21). It has a distal tendon that inserts into the lateral side of the base of the proximal phalanx of the minimus; this tendon usually blends laterally with that of abductor digiti minimi. Occasionally, some of its deeper fibres extend to the lateral part of the distal half of the fifth metatarsal bone, constituting what may be described as a distinct muscle, opponens digiti minimi.

Relations

The fifth metatarsal shaft lies on the deep surface of flexor digiti minimi brevis, the interossei lie medially and abductor digiti minimi is lateral. The most lateral branch of the lateral plantar nerve lies superficially and just medial to flexor digiti minimi brevis.

Vascular supply

Flexor digiti minimi brevis is supplied by end twigs of the arcuate and lateral tarsal arteries, and the lateral plantar artery and its digital (plantar) branch to the lateral side of minimus.

Innervation

Flexor digiti minimi brevis is innervated by the super-ficial branch of the lateral plantar nerve, S2 and S3.

Action

Flexor digiti minimi brevis flexes the metatarsophalangeal joint of the little toe.

Attachments

The dorsal interossei (Fig. 84.22A) are situated between the metatarsal bones. They consist of four bipennate muscles, each arising by two heads from the sides of the adjacent metatarsal bones. Their tendons are attached to the bases of the proximal phalanges and to the dorsal digital expansions. The first inserts into the medial side of the second toe; the other three pass to the lateral sides of the second, third and fourth toes.

Fig. 84.22 The interossei of the left foot. A, Dorsal interossei viewed from the dorsal aspect. B, Plantar interossei viewed from the plantar aspect. The axis to which the movements of abduction and adduction are referred is indicated.

Relations

Between the heads of each of the three lateral muscles, there is an angular space through which a perforating artery passes to the dorsum of the foot. Between the heads of the first muscle, the corresponding space transmits the terminal part of the dorsalis pedis artery to the sole (see Fig. 84.1).

Vascular supply

Dorsal interossei are supplied by the arcuate artery, lateral and medial tarsal arteries, the first to fourth plantar arteries and the first to fourth dorsal metatarsal arteries (receiving proximal and distal perforating arteries), and by the dorsal digital arteries of the lateral four toes.

Innervation

Dorsal interossei are supplied by the deep branch of the lateral plantar nerve (S2 and S3), except that of the fourth interosseous space, which is supplied by the superficial branch of the lateral plantar nerve.

Action

Dorsal interossei abduct the toes relative to the longitudinal axis of the second metatarsal. They also flex the metatarsophalangeal joints and extend the interphalangeal joints of the lesser toes. The hallux and little toe have their own abductors.

Clinical anatomy

Denervation of the interossei leads to claw-toe deformities. Development of claw toes should alert the clinician to the possibility of a neuropathic process (e.g. Charcot–Marie–Tooth disease, diastematomyelia).

Relations

The plantar interossei lie plantar to the dorsal interossei and deep to the muscles of the third layer.

Vascular supply

Plantar interossei are supplied by the lateral plantar artery, the plantar arch, the second to fourth plantar metatarsal arteries and the dorsal digital arteries of the lateral three toes.

Innervation

Plantar interossei are supplied by the deep branch of the lateral plantar nerve (S2 and S3), except that of the fourth interosseous space, which is supplied by the superficial branch of the lateral plantar nerve.

Action

Plantar interossei adduct the third, fourth and fifth toes, flex the metatarsophalangeal joints and extend the interphalangeal joints.

Clinical anatomy

The clinical anatomy of the plantar interossei is similar to that of the dorsal interossei.

Attachments

Extensor digitorum brevis (Fig. 84.2A) is a thin muscle which arises from the distal part of the superolateral surface of the calcaneus in front of the shallow lateral groove for fibularis brevis, from the interosseous talocalcaneal ligament, and from the deep surface of the stem of the inferior extensor retinaculum. It slants distally and medially across the dorsum of the foot, and ends in four tendons. The medial part of the muscle is usually a more or less distinct slip, ending in a tendon that crosses the dorsalis pedis artery superficially to insert into the dorsal aspect of the base of the proximal phalanx of the hallux; this slip is sometimes termed extensor hallucis brevis. The other three tendons attach to the lateral sides of the tendons of extensor digitorum longus for the second, third and fourth toes.

The muscle is subject to much variation, e.g. accessory slips from the talus and navicular, an extra tendon to the fifth digit, an absence of one or more tendons. It may be connected to the adjacent dorsal interosseous muscles.

Relations

The most medial tendon, that of extensor hallucis brevis, courses dorsomedially and passes superficial to the dorsalis pedis artery and the deep fibular nerve. The remaining three tendons pass obliquely deep to the corresponding tendons of extensor digitorum longus.

Vascular supply

Extensor digitorum brevis is supplied by the anterior perforating branch of the fibular artery, the anterior lateral malleolar artery, lateral tarsal arteries, dorsalis pedis arteries, arcuate artery, the first, second and third dorsal metatarsal arteries, proximal and distal perforating arteries, and the dorsal digital arteries to the medial four toes (including the hallux).

Innervation

Extensor digitorum brevis is supplied by the lateral terminal branch of the deep fibular nerve, L5, S1.

Actions

The muscle assists in extending the phalanges of the middle three toes via the tendons of extensor digitorum longus; in the hallux, it assists in extension of the metatarsophalangeal joint.

Clinical anatomy

Laceration of extensor digitorum brevis leads to little in the way of functional impairment, because the long extensors can compensate for the loss of the muscle. The proximal part of the muscle can be used as interposition material to prevent bone fusion after resection of a calcaneonavicular bar (a common tarsal coalition). The muscle belly and tendon of extensor hallucis brevis serve as guides to the location of the dorsalis pedis artery and deep fibular nerve. The tendon of extensor hallucis brevis can be used as a local graft.

Tarsal arteries

There are two tarsal arteries, lateral and medial (Fig. 84.23). They arise as the dorsalis pedis artery crosses the navicular. The lateral runs laterally under extensor digitorum brevis; it supplies this muscle and the tarsal articulations, and anastomoses with branches of the arcuate, anterior lateral malleolar and lateral plantar arteries, and the perforating branch of the fibular artery. Two or three medial tarsal arteries ramify on the medial border of the foot and join the medial malleolar network.

Arcuate artery

The arcuate artery (Fig. 84.23) arises near the medial cuneiform, passes laterally over the metatarsal bases, deep to the tendons of the digital extensors, and anastomoses with the lateral tarsal and plantar arteries. It supplies the second to fourth dorsal metatarsal arteries, running distally superficial to the corresponding dorsal interossei, and divides into two dorsal digital branches for the adjoining toes in the interdigital clefts. Proximally, in the interosseous spaces, these branches receive proximal perforating branches from the plantar arch. Distally, they are joined by distal perforating branches from the plantar metatarsal arteries. The fourth dorsal metatarsal artery sends a branch to the lateral side of the fifth toe.

First dorsal metatarsal artery

The first dorsal metatarsal artery (Fig. 84.23) arises just before the dorsalis pedis artery enters the sole. It runs distally on the first dorsal interosseous and divides at the cleft between the first and second toes. One branch passes under the tendon of extensor hallucis longus and supplies the medial side of the hallux; the other bifurcates to supply the adjoining sides of the hallux and the second toe.

Cutaneous vessels from the dorsalis pedis artery

The dorsalis pedis artery and its first dorsal metatarsal branch give rise to small direct cutaneous branches that supply the dorsal foot skin between the extensor retinaculum and the first web space. This vessel provides the basis for a fasciocutaneous flap raised from this region, and which may be used to cover superficial defects elsewhere.

Medial plantar artery

The medial plantar artery is the smaller terminal branch of the posterior tibial artery (Fig. 84.24). It arises midway between the medial malleolus and the medial calcaneal tubercle and passes distally along the medial side of the foot, with the medial plantar nerve lateral to it. At first deep to abductor hallucis, it runs distally between abductor hallucis and flexor digitorum brevis, supplying both. Near the first metatarsal base, when its calibre is already diminished as a result of supplying numerous muscular branches, it is further diminished by a superficial stem. It passes to the medial border of the hallux, where it anastomoses with a branch of the first plantar metatarsal artery. Its superficial stem then trifurcates and supplies three superficial digital branches that accompany the digital branches of the medial plantar nerve and join the first to third plantar metatarsal arteries.

Lateral plantar artery

The lateral plantar artery is the larger terminal branch of the posterior tibial artery (Fig. 84.24). It passes distally and laterally to the fifth metatarsal base; the lateral plantar nerve is medial. The plantar nerves lie between the plantar arteries. Turning medially, with the deep branch of the nerve, it gains the interval between the first and second metatarsal bases, and unites with the dorsalis pedis artery to complete the plantar arch. As it passes laterally, it is first between the calcaneus and abductor hallucis, then between flexor digitorum brevis and flexor accessorius. Running distally to the fifth metatarsal base, it passes between flexor digitorum brevis and abductor digiti minimi and is covered by the plantar aponeurosis, superficial fascia and skin.

Muscular branches supply the adjoining muscles. Superficial branches emerge along the intermuscular septum to supply the skin and subcutaneous tissue over the lateral part of the sole. Anastomotic branches run to the lateral border, and join branches of the lateral tarsal and arcuate arteries. Sometimes, a calcaneal branch pierces abductor hallucis to supply the skin of the heel.