Bilateral Fusion of the Semitendinosus and Long Head of the Biceps Femoris Muscles in a Male Cadaver.

Bilateral variation of the semitendinosus (ST) and the long head of the biceps femoris (BFlh) muscles is an anatomically rare occurrence. In this case report, we describe a male cadaver exhibiting bilateral fusion of the ST and BFlh muscles at their proximal origin on the ischial tuberosity, with the muscles separating distally into their respective muscle bellies. As far as we are aware, this bilateral fusion has not been previously documented in the literature; the only known report of fusion between the ST and BFlh muscles describes a unilateral fusion in a female cadaver, which was associated with a unilateral muscular slip that was not seen on either side of the bilateral fusion of our male cadaver. This bilateral fusion may have significant clinical implications regarding hamstring biomechanics, susceptibility to muscle strain, tendon injury, and possible sciatic nerve irritation or entrapment. Awareness of such variations may guide orthopedic surgeons, neurologists, radiologists, sports medicine specialists, and rehabilitation clinicians in accurate diagnosis and effective management of posterior thigh and lower extremity disorders.