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Hamstring Regrows but Doesn't Regain Full Strength after ACL Repair

A torn anterior cruciate ligament (ACL) can be repaired using a piece of the hamstring tendon (the graft). The missing tendon grows back. But does the hamstring have its full strength and function after recovery? This study measures how much hamstring tendon tissue grows back. The study compares how much tissues grows back to the strength of the hamstring muscle.

Twenty-eight patients were followed for at least two years. All patients had a hamstring tendon graft to repair a torn ACL. The graft was taken from the same leg as the ACL injury. MRIs were taken of both knees for comparison. Hamstring strength was measured in three positions.

The results showed that tissue regrowth occurred so that the tendons were the same size on both sides. Strength was still less on the graft side. In the prone position (face down) using full knee flexion, the hamstring had only half the strength of the healthy hamstring.

The authors report that even if the tendon grows back at the graft site, normal strength is not regained. The position affected the most is deep flexion. Gymnasts performing on floor exercises and on the balance beam use this position. Wrestlers and judo athletes also have trouble using a hooking action that requires full knee flexion when lying on the mat.

More study is needed to find out what keeps the hamstring from regaining full strength. There may be more than one factor involved. It may depend on which hamstring tendon is used. Or the healthy leg may get stronger as the patient favors the leg that was weakened by surgery. The result could be added hamstring weakness from more than just the tissue graft.

References: Kou Tadokoro, MD, et al. Evaluation of Hamstring Strength and Tendon Regrowth after Harvesting for Anterior Cruciate Ligament Reconstruction. In The American Journal of Sports Medicine. October/November 2004. Vol. 32. No. 7. Pp. 1644-1650.

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