Anatomic variations of the musculotendinous junction of the soleus muscle and its clinical implications

The soleus muscle, like the gastrocnemius, is a powerful plantarflexor muscle in the lower limb. The soleus muscle joins the aponeurosis of the gastrocnemius muscle to form the calcaneal (Achilles) tendon. While the basic anatomy of the soleus muscle has been previously described, no study has addressed the anatomical variations of its distal attachment. We found considerable anatomic variation in the distance between this musculotendinous junction and the most proximal point of the proximal edge. This distal measuring point was defined as the most proximal point of the proximal edge of the posterior surface of the calcaneal tuberosity. Eighty human cadaver specimens were preserved according to Thiel's method; we examined one limb from each cadaver, studying 80 lower extremities in total. Following careful dissection of the lower limb, we measured the distance between the distal point of attachment of the soleus muscle fibers (the musculotendinous junction) and the designated measuring point. Our findings were divided into three groups: Group 1 (10 cases, 12.5%), where the distance between the musculotendinous junction and the designated point on the calcaneal tuberosity was between 0 and 1 inches; Group 2 (56 cases, 70%), where the distance was between 1 and 3 inches; and Group 3 (14 cases, 17.5%), where the distance was greater than 3 inches. Detailed knowledge of the anatomic variations of the soleus muscle at its insertion point onto the calcaneal tendon has clinical implications in calcaneal tendon repair following rupture and in the planning of reconstructive surgery using soleus muscle flaps.