Compartments of the leg

Anterior surface

Tibialis anterior originates from the proximal half to two-thirds of the lateral tibia. Descending inferomedially across the anterior aspect of the leg, the muscle becomes tendinous before inserting on to the first metatarsal and medial cuneiform. Lying lateral to tibialis anterior, extensor digitorum longus arises from the lateral condyle of the tibia and proximal three-quarters of the medial fibula. The muscle passes inferiorly, becoming tendinous at approximately the same level as tibialis anterior, prior to dividing into four slips and inserting on to phalanges two to five. Extensor hallucis longus lies between, and is partially overlapped by, tibialis anterior and extensor digitorum longus. Its origin is from the middle half of the medial fibula, medial to that of extensor digitorum longus; its fibres end in a tendon that runs along the anterior aspect of the muscle and passes deep to the inferior extensor retinaculum to insert on to the dorsal aspect of the base of the distal phalanx of the great toe. Fibularis tertius arises from the distal third of the medial fibula and inserts on to the dorsal surface of the fifth metatarsal.

The anterior tibial artery emerges into the anterior compartment above the interosseous membrane. It then runs along the anterior aspect of the interosseous membrane, lying proximally between tibialis anterior and extensor digitorum longus, and distally between tibialis anterior and extensor hallucis longus. The common fibular nerve can often be palpated as a firm cord curving laterally around the neck of the fibula. It proceeds deep to fibularis (peroneus) longus, bifurcating into the superficial and deep fibular nerves. Proximally, the superficial fibular nerve runs deep to fibularis longus. It emerges anterolaterally in the distal third of the fibula, passing between fibularis longus and brevis and extensor digitorum longus before branching into the medial and intermediate dorsal cutaneous nerves. The deep fibular nerve runs anterior to the interosseous membrane, travelling with the anterior tibial artery in the distal two-thirds of the leg ( Fig. 84.1A ).

Posterior surface

Gastrocnemius is the most superficial muscle of the posterior leg. Its two heads have tendinous attachments to the lateral and medial condyles of the femur. Its muscle fibres extend to approximately mid-calf, where they begin to insert into a broad aponeurosis on its anterior surface. The aponeurosis gradually narrows and receives the tendon of soleus on its deep surface to form the calcaneal (Achilles) tendon. Soleus lies deep to gastrocnemius, originating from the posterior aspect of the head of the fibula, the proximal quarter of the body of the fibula, and the soleal line. Tibialis posterior, flexor digitorum longus and flexor hallucis longus comprise the deep flexor group of the leg. Flexor digitorum longus lies deep to soleus, originating from the posteromedial tibia. Flexor hallucis longus arises from the distal two-thirds of the posterior fibula and travels inferolaterally to pass posterolateral to flexor digitorum longus at the ankle. It lies deep to the calcaneal tendon and soleus, and lateral to flexor digitorum longus. Tibialis posterior arises between flexor hallucis longus and flexor digitorum longus from the upper two-thirds of the posteromedial fibula, lateral posterior tibia and intraosseous membrane.

The posterior tibial artery runs through the flexor compartment and bifurcates into the medial and lateral plantar arteries midway between the medial malleolus and calcaneal tubercle, deep to abductor hallucis. The artery travels posterior to tibialis posterior, flexor digitorum longus, the tibia and the ankle joint, sitting lateral to extensor hallucis longus. The fibular artery branches off the posterior tibial artery, travelling obliquely to the fibula, and descending either between tibialis posterior and flexor hallucis longus or within flexor hallucis longus. The long saphenous vein arises anterior to the medial malleolus and follows an anteroposterior course over the distal third of the medial tibia before travelling superiorly along the medial aspect of the leg. The tibial nerve descends alongside the posterior tibial artery and veins. It begins deep to soleus and gastrocnemius, passing superficially in the distal third of the leg. Distally, the sural nerve descends lateral to the calcaneal tendon, near the short saphenous vein, and supplies the posterior and lateral skin of the distal third of the leg. It then passes distal to the lateral malleolus along the lateral side of the foot and fifth toe, supplying the overlying skin ( Fig. 84.1B ).

Lateral surface

Fibularis longus, the most superficial of the two lateral compartment muscles, originates on the head and proximal two-thirds of the lateral fibula, the deep surface of the deep fascia and the anterior and posterior intermuscular septa; the common fibular nerve passes between its attachments to the head and shaft of the fibula. Proximally, fibularis longus lies posterior to extensor digitorum longus and anterior to soleus and flexor hallucis longus. Distally, it runs posterior to fibularis brevis and ends in a tendon that passes posterior to the lateral malleolus, crosses the sole of the foot obliquely and is attached to the lateral side of the base of the first metatarsal and the lateral aspect of the medial cuneiform ( Ch. 86 ). Fibularis brevis originates from the distal two-thirds of the lateral fibula and posterior crural intermuscular septum. It passes downwards, ending in a tendon that passes behind the lateral malleolus together with, and anterior to, that of fibularis longus. It is inserted into a tuberosity on the lateral side of the base of the fifth metatarsal.