Accessory soleus muscle: a case report and clinical applicability

Abstract

Variations in leg muscle are uncommon. Literature on this subject is scarce, but when those variations are reported they may cause alterations in joint mechanics or cause some discomfort in the leg and foot. The accessory soleus muscle (ASM) is considered an unusual anatomical variation, with an incidence of 0.5-6.0% in the population through studies in cadavers. During routine preparation of study material in the dissection room of the anatomy laboratory of the Escola Superior de Ciências da Santa Casa de Misericórdia de Vitória/ES – Brazil, an ASM was found in the right inferior limb of a male cadaver fixed in 10% formalin. This supernumerary muscle was 3 cm wide, 9 cm long and 1 cm thick in its most voluminous part, in typical penniform fibers arrangement. It was located in the posteromedial region of the ankle, anterior to the Achilles tendon and posterior to the deep muscles of the leg compartment. Its anterior face covered the tibial nerve and the posterior tibial vessels, while its lower half was covered by the flexor retinaculum into the tarsal tunnel. Reports in the literature show possible compression of a neurovascular bundle because of its intimal position within the tarsal tunnel, which could result in ischemic compartment syndrome.

Presence of Accessory Soleus Muscle in Cadaver: Case Report

“…Variations in the muscles of the posterior leg region can lead to chronic painful conditions of the ankle. ASM is a condition that manifests itself with the increase in clinical problems caused by advanced age (13)(14)(15)(16)(17). ASM, whose incidence was reported as 0.7%-5.5% in cadaver studies, is usually unilateral and it has been reported to be more (4,18,19).…”

Accessory Soleus Muscle: Two Case Reports with a Completely Different Presentation Caused by the Same Entity

“…Although congenital, ASM is usually diagnosed in the second or third decade of life when symptoms occur. During this period, muscle mass and physical activity increase, more prominently seen in male patients [ 7 , 8 ].…”

Imaging of Tendinous and Muscular Anatomical Variants Around the Ankle

“…[1][2][3]11,12 The AS muscle is usually unilateral and shows male predilection, 3,11 presumably due to greater muscle trophism and denser muscle fascia in males. 14 The muscle originates either from the anterior surface of the soleus muscle, the fibula, or the soleal line of the tibia. [1][2][3]11,12 The AS muscle is located superficially to the deep aponeurosis.…”

“…1 2 3 11 12 The AS muscle is usually unilateral and shows male predilection, 3 11 presumably due to greater muscle trophism and denser muscle fascia in males. 14…”

“…1 3 16 An alternative explanation is that the AS muscle may compress on the adjacent posterior tibial nerve on its course through the tarsal tunnel, causing compressive neuropathy, resulting in pain and sometimes even involuntary movements of the second to fifth toe. 1 3 11 14 16 The AS muscle is also associated with clubfoot deformity and Achilles tendinopathy. 3 Symptomatic patients have been treated successfully with fasciotomy, tendon release, and/or excision.…”