Le muscle soléaire accessoire

The accessory soleus muscle is found in 10% of individuals. It is often asymptomatic. The muscle inserts on the anterior aspect of the soleus muscle or on the posterior aspect of the tibia or the muscles of the deep posterior compartment. It lies anterior to the calcaneal tendon and terminates on the calcaneal tendon or the superior or medial aspect of the calcaneus via fleshy fibers or a distinct tendon. Frequent in primates, this anatomic variant is present during embryological development. Its persistence depends on phylogenetic evolution. Among other hypotheses (exercise-induced intermittent claudication, compression of the tibial nerve, excessive tension on the nerve innervating the accessory soleus muscle), this supranumerary muscle is generally considered to be the cause of a localized compartment syndrome. Pain experienced during exercise is the only symptom regularly reported by patients. A careful examination is required to rule out another local cause. Besides tumefaction lateral to the Achilles tendon, often found bilaterally, there is no other clinical sign. Plain x-rays, ultrasound and computed tomography simply demonstrate a “mass” in front of the Achilles tendon. MRI is the examination of choice enabling confirmation of the muscle nature of the mass and ruling out the possible diagnosis of tumor. Since there is no risk of aggravation, surgical treatment can be avoided if there is no complaint. If the patient is seriously impaired, surgery can be proposed. In our opinion, complete resection of the supernumerary muscle is the safest solution and should be preferred over simple fasciotomy.