Biomechanics of anterior cruciate ligament reconstruction using twisted doubled hamstring tendons

We studied the biomechanical properties of a twisted doubled semitendinosus and gracilis graft. We applied an un-axial load in order to reproduce the kinematics of a reconstructed anterior cruciate ligament (ACL). A modified cryo-jaw clamp system was used to minimize soft tissue slippage. The lower grip, after fixation of the free ends of the tendons, was rotated 45degrees, translated 1 cm, and bent 40degrees, simulating a knee sprain. The graft was tested to failure using a servohydraulic machine. The specimen from one knee of seven unembalmed cadavers was assigned to the untwisted (parallel) bundles group, while its pair was assigned to the twisted group. For the parallel bundles group, the mean maximum load was 1709.3+/-581.9 N, for the twisted group 2428.3+/-475.4 N (P<0.05). The mean stiffness was respectively 213.6+/-72.4 N/mm and 310.3+/-97.3 N/mm (P=0.08). Although caution should be used in extrapolating the results to clinical estimates of the strength of hamstring grafts, the results of the present study could justify the use of twisted semitendinosus and gracilis bundles in ACL reconstruction.