Biomechanical Analysis of Two Different Tibial Fixation Methods for Anterior Cruciate Ligament Reconstruction Using Soft Tissue Graft: An Experimental Study in Sheep Knees

The performance of tibial fixation methods of soft tissue graft (ACL) using interference screw and suture disc is studied in the paper. Tendoachillis graft was harvested from 16 fresh-frozen hind limbs from mature sheeps and double folded graft was used for fixation through a tibial tunnel.  Two groups of   mechanical test specimens of 8 each according to the fixation technique are made, as group A (suture disc) and group B (interference screw).  The first 4 specimens were used for tensile test and the rest was used for cyclic fatigue test, with specimens undergoing a preconditioning procedure before actual testing. The study and test results shows that the mean yield load for graft fixed with interference screw  is 246.5N and was comparable with the yield load for the graft fixed with suture disc which is 222.7 N. But the mean elongation for suture disc and interference screw is 17.71 and 12.19 respectively.  So the interference screw fixation for soft tissue graft at tibial side has comparable pull out strength and stiffness as that of suture disc. (p > 0.05) The elongation for the graft fixed with the suture disc is more than that of the graft fixed with interference screw. This difference in elongation between suture disc group and interference screw group is statistically significant. (p=0.02, Unpaired T test)  This indicates that the chance of residual laxity and slippage is more in suspensory fixation modality.  Interference screw fixation for soft tissue graft has less elongation and residual laxity and could be an ideal fixation device for tibial fixation of soft tissue graft.