This muscular compartment lies between the peroneal surface of the fibula and deep fascia of the leg and is bounded in front and behind by the anterior and posterior intermuscular septa. It contains the peroneus longus and brevis muscles and the superficial peroneal nerve. Its blood supply is derived from branches of the peroneal artery which pierce flexor hallucis longus and the posterior intermuscular septum. Its veins drain, for the most part, into the small saphenous vein.
Peroneus longus and peroneus brevis
Peroneus (fibularis) longus arises from the head and the upper two-thirds of the peroneal surface of the fibula and from the intermuscular septa. Peroneus (fibularis) brevis arises from the lower two-thirds of the fibula; in the middle third of the bone its origin lies in front of that of peroneus longus and the two muscles, and their tendons maintain this relationship.
The broad tendon of peroneus brevis lies behind (and grooves) the lateral malleolus. The narrower tendon of peroneus longus lies on that of brevis and does not come into contact with the malleolus. The two tendons pass forwards to the peroneal trochlea on the lateral surface of the calcaneus, which separates them. The tendon of brevis passes above the peroneal trochlea to be inserted into the tubercle at the base of the fifth metatarsal bone. The tendon of peroneus longus passes below the peroneal trochlea and enters the sole of the foot, lying against the posterior ridge of the groove on the cuboid bone. Here the tendon possesses a sesamoid fibrocartilage which often ossifies. The tendon crosses the sole obliquely to be inserted into the lateral side of the base of the first metatarsal and the adjoining part of the medial cuneiform (Fig. 3.38).
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Figure 3.38 Plantar muscles and tendons of left foot: fourth layer. |
The tendons are bound down at the lateral malleolus by the superior peroneal retinaculum, a band of deep fascia that extends from the back of the malleolus to the lateral surface of the calcaneus; and at the peroneal trochlea by the inferior peroneal retinaculum, a band of fascia attached to the peroneal trochlea and to the calcaneus above and below the peroneal tendons. Its upper part is continuous with the stem of the Y-shaped inferior extensor retinaculum. The two tendons are enclosed in a common synovial sheath from above the lateral malleolus to the peroneal trochlea, where the sheath divides to accompany each tendon separately to its insertion.
Nerve supplies. Both muscles are supplied by the superficial peroneal nerve (L5, S1).
Action. Both muscles evert, and weakly plantarflex, the foot; they are the plantarflexors when the tibial nerve is paralysed. In addition, peroneus longus is a factor in maintaining the lateral longitudinal and transverse arches of the foot (see p. 161).
Test. The foot is everted and the tendons can be seen and felt below the lateral malleolus.
The superficial peroneal (superficial fibular) nerve begins in the substance of peroneus longus at the division of the common peroneal nerve. It passes downwards in the muscle and emerges at its anterior border behind the anterior intermuscular septum. It supplies both peronei, pierces the deep fascia between the middle and lower third of the leg, and divides into medial and lateral branches. (The distribution on the dorsum of the foot has been described on page 145.) It also supplies the skin of the anterolateral aspect of the lower leg (Fig. 3.46).
