Dr. Ebraheim’s educational animated video describes the anatomy of the peroneal muscles of the lower leg.
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Anatomy of the Peroneal Muscles Lower Leg
The peroneal muscles are a group of three muscles: peroneus longus, peroneus brevis, and peroneus tertius. Other muscles may exist. The peroneus longus and brevis muscles lie within the lateral compartment and the peroneus tertius muscle is located within the anterior compartment of the leg. The peroneus longus muscle arises from the upper 2/3 of the lateral surface of the fibula. The peroneus tertius muscle arises from the lower ¼ - 1/3 of the anterior portion of the medial surface of the fibula. The peroneus longus is the longest and most superficial muscle of the lateral compartment. The tendon of the peroneus longus muscle begins at a higher level than the tendon of the peroneus brevis and can easily be recognized on ultrasound. The peroneus longus is lateral and posterior to the peroneus brevis muscle. Near the ankle and on the ultrasound image, the peroneus longus appears as a tendon while the peroneus brevis may appear as a muscle. The peroneus longus muscle is inserted into two bones: the base of the first metatarsal and adjoining portion of the medial cuneiform bone. Before the peroneus longus insertion, the tendon makes three turns. The first turn is at the tip of the lateral malleolus. The second turn occurs below the trochlear process of the calcaneus. And finally, it turns at the groove of the cuboid crossing the plantar surface of the foot obliquely. The peroneus brevis muscle is inserted into the tuberosity of the base of the 5th metatarsal bone. Avulsion fracture of the 5th metatarsal base may occur from the pull of the peroneus brevis tendon. The peroneus brevis muscle can be used as a flap to reconstruct a small defect of the distal third of the lower leg. The peroneus tertius muscle is inserted into dorsal surface of the base of the 5th metatarsal bone. The location of the anterolateral ankle arthroscopy portal (which is the second portal, the first portal is usually medial) should lie just lateral to the peroneus tertius tendon. Staying lateral to the peroneus tertius tendon helps avoid injury to the dorsal lateral branch of the superficial peroneal nerve. The peroneal muscles are situated on the outer side of the lower leg and their tendons attach to the foot. Near the ankle, the peroneus brevis is closer to the fibula. There are two peroneal retinacula which holds the two peroneal tendons: superior peroneal retinaculum (important) and inferior peroneal retinaculum (not that important in holding the tendons in its position behind the fibula). Rupture of the superior peroneal retinaculum may cause peroneal tendon subluxation and the subluxation may be acute, chronic, or recurrent. Acute rupture of the superior peroneal retinaculum allows for subluxation of the peroneal tendons and may cause disability to the ankle and to the patient. Retromalleolar pain on active eversion is a specific and highly suggestive finding for dislocation of the peroneal tendons. Injury to the peroneal tendons is a frequently overlooked cause of persistent lateral ankle pain after trauma. The most reliable sign is persistent swelling along the posterolateral edge of the fibula. A pathognomonic sign for peroneal tendon subluxation is an avulsion of a piece of bone from the fibula. The “fleck sign” is an indication for peroneal tendon subluxation. Sometimes we call this avulsion fracture of the fibula the rim fracture. The piece of bone from the avulsion fracture is long and thin. Tear of the superior retinaculum may be misdiagnosed because of the associated pain, swelling, and ecchymosis that may hinder early diagnosis. Pain associated with peroneal tendonitis is located behind the lateral malleolus. Cavovarus foot deformity with weakness of the tibialis anterior, peroneus brevis, and intrinsic muscles. The tibialis posterior function is normal. The peroneus longus is not affected, causing plantar flexion of the first ray resulting in cavus foot deformity. Peroneus longus spasm can occur with tarsal coalition in the foot, and it may occur with rheumatoid arthritis and other conditions. In polio, the transfer of the peroneus longus muscle in the presence of a strong tibialis anterior muscle will result in a dorsal bunion as the forefoot supinates. It must be combined with lateral transfer of the tibialis anterior muscle to the base of the second metatarsal bone. The shaft of the first metatarsal is dorsiflexed, and the big toe is plantar flexed as seen when there is imbalance between the tibialis anterior muscle and the peroneus longus muscle. The peroneus longus and peroneus brevis muscles receive their innervation from the superficial peroneal nerve. The peroneus tertius muscle is considered to be the lower lateral part of the extensor digitorum longus muscle.
