The peroneus longus originates from the proximal lateral fibula and inserts on the plantar aspect of the medial cuneiform and the base of the first metatarsal. The peroneus brevis originates from the distal lateral fibula and inserts on the base of the fifth metatarsal. On axial images, the peroneus longus tendon is located posterolateral to the peroneus brevis tendon (Fig. 19). Both are innervated by the superficial peroneal nerve and act to evert the foot. The peroneus longus also inhibits varus displacement of the first metatarsal . Although peroneal tendon pathology is common, it can be difficult clinically to distinguish injuries to the peroneal tendons from lateral ankle ligament injuries
after an ankle sprain . Peroneal tendon pathology can be a cause of chronic lateral ankle pain and disability . Acute injuries to the peroneus brevis include partial or complete tear (Fig. 20), avulsion from its insertion, with or without osseous avulsion fracture, or subluxation (Fig. 21) . Chronic injuries to the peroneus brevis include tendinosis or a longitudinal split (Fig. 22) . Some authors have described a hypovascular zone of the pero-neus brevis tendon at the level of the fibular groove, suggesting that this is a contributing factor to development of tendinosis or split of the tendon . However, other authors contend that no hypovascular zone can be found that correlates with the site of tendon splits . Surgical intervention for small or low-grade tears of the peroneus brevis includes debridement or repair, while in more severe tears, resection of the damaged tendon with tenodesis to the peroneus longus is performed . Peroneus longus injuries include acute tear, tendinosis, or chronic longitudinal tears (Fig. 23) . As with other tendons, partial tear is seen as thickening and heterogeneous signal intensity at MRI, while complete tears manifest discontinuity of the tendon . Additional findings such as fluid in the peroneal tendon sheath, an enlarged peroneal tubercle (Fig. 24), or peroneus brevis tear are often associated with peroneus longus tears .
The primary restraint to peroneal tendon subluxation or dislocation is the superior peroneal retinaculum (Fig. 21) . Injury to the retinaculum is usually associated with lateral ankle ligament sprains . Soft tissue reconstruction of the superior peroneal retinaculum is performed with various techniques, one of which uses a periosteal flap from the posterior distal fibula to reinforce the retinaculum . Postsurgical or posttraumatic scarring can occasionally cause tethering of the peroneal tendon sheath or the sural nerve
Fig. 20. Axial image demonstrates the peroneus longus tendon (white arrow), located posteromedial to the peroneus brevis tendon (black arrow).
The peroneus quartus is an accessory muscle found in about 7% of patients (Fig. 26). It originates from the peroneus brevis muscle, and inserts on the ret-rotrochlear eminence of the calcaneus . Its presence is usually incidental, but can be associated with a longitudinal tear of the peroneus brevis .
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