Peroneus longus is one of the muscles of the lateral crural compartment of the leg. It arises from the:
- superior two thirds of the lateral shaft of the fibula
- head of the fibula
- anterior and posterior crural intermuscular septa
From these sites it forms a narrow muscle passing distally from the fibula. Throughout this course, it is superficial to peroneus brevis. Nearing the ankle it becomes tendinous and passes posterior to the lateral malleolus which it uses as a pulley. It is constrained posterior to bone by the superior peroneal retinaculum. At this point, it is in a common synovial sheath with peroneus brevis. Beyond the lateral malleolus it passes anteroinferiorly to descend posterior to the peroneal trochlea on the calcaneus into a groove on the inferior surface of the cuboid bone. This groove redirects the tendon anteriorly and medially across the sole of the foot to insert into the base of the plantar surface of the first metatarsal and the plantar surface of the medial cuneiform bone.
It is innervated by the superficial peroneal nerve (L5,S1).
Peroneus longus acts to:
- plantarflex the foot
- evert the foot
- support the transverse and longitudinal arches