The long head of biceps femoris arises via a long flat tendon from the ischial tuberosity, sharing the common hamstring origin with the semitendinosus and semimembranosus. The proximal biceps femoris tendon is the most lateral of the proximal hamstring tendons, with the semitendinosus arising from its medial surface in a conjoint origin arrangement. Proximal biceps femoris tendon avulsion from the ischial tuberosity is a distinct injury pattern from the more common mid-substance hamstring strain.
Proximal hamstring avulsion (complete or partial avulsion of the conjoint biceps-semitendinosus and/or semimembranosus from the ischial tuberosity) occurs with sudden hip flexion and knee extension (water skiing, sprinting starts). MRI grading identifies the degree of retraction and whether the avulsion is complete (surgical) or partial (conservative or surgical for athletes). Operative repair with suture anchors or transosseous fixation to the ischial tuberosity within 4 weeks of injury produces significantly better outcomes than late repair. Chronic retracted avulsions produce hamstring weakness, sitting discomfort, and sciatic nerve irritation from scar formation around the nerve.
Sudden hip flexion with knee extension avulses the conjoint biceps femoris and semitendinosus from the ischial tuberosity, producing posterior thigh bruising, weakness of knee flexion, and a palpable defect below the ischial tuberosity; MRI confirms complete avulsion with retraction and early operative repair with suture anchors to the ischium restores hamstring strength.
