Unilateral Tensor Fascia Suralis: A Rare Type Ia Variant and Its Clinical Implications.

Tensor fascia suralis is a rare supernumerary muscle in the posterior thigh and leg, with a male preponderance as reported in the literature. We present a unique Type Ia variant discovered during cadaver dissection of the left lower limb, originating from the long head of the biceps femoris and terminating at the medial head of the gastrocnemius. Unlike previously reported cases, this variant exhibited two distinct fleshy muscle bellies at origin and insertion, separated by an intermediate tendon. Both bellies received innervation from the tibial nerve, with the upper belly supplied directly via the sciatic nerve and the lower belly via a branch penetrating the gastrocnemius. This anomaly has significant clinical implications, potentially mimicking soft tissue tumors on imaging or contributing to nerve compression syndromes. Awareness of such variants is crucial for accurate diagnosis and optimizing surgical outcomes in posterior thigh and leg procedures.