Medial hamstring tendon regeneration following harvest for anterior cruciate ligament reconstruction: fact, myth, and clinical implication.

It has been demonstrated that the medial hamstring tendons regenerate in the majority of patients following their harvest for anterior cruciate ligament reconstruction. The anatomy and morphology of these regenerated tendons have been radiographically and surgically documented. The neotendons originate within the appropriate muscle belly but display an altered insertion anatomy. Their histological composition is largely tendinous but has regions that resemble scar tissue. Concordantly, an animal model indicates that the neotendon has decreased mechanical strength, which has implications for tendon re-harvest. The regenerated tendons do restore a muscle tendon complex that is able to generate force; however, strength testing indicates that the function of the hamstring muscles is altered by harvest and regeneration. The most significant strength deficits are present in deep knee flexion and internal rotation of the tibia, whereas the peak torque of knee flexion is minimally affected. Additional harvest of the gracilis tendon results in greater deficits. The current literature indicates that hamstring tendon regeneration does indeed occur, but with structural and functional alterations.