O1077 THE BIOMECHANICAL PROPERTIES OF FOUR METHODS OF FIXATION USED FOR HAMSTRING TENDON ANTERIOR CRUCIATE LIGAMENT GRAFTS

Abstract

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of four methods of fixation of hamstring anterior cruciate ligament (ACL) grafts. A 2-strand equine extensor tendon graft model was used because a previous study has shown it to have equivalent biomechanical properties to that of 4-strand human semitendinosus and gracilis tendon grafts. Method: Twenty stifle joints were obtained from 10 skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday rhino horn jig to accurately position a guide wire over which an 8mm tunnel was drilled. A 2-strand equine tendon graft was then introduced into the tibial tunnel and secured with either a titanium round headed cannulated interference (RCI) screw, a bioabsorbable RCI screw, an Endobutton or an expansile Bollard. Five of each method of fixation were tested mechanically to ultimate failure and under cyclical loading. Results: The mean ultimate tensile loads (UTL) were: titanium RCI screw = 444 N, bioabsorbable RCI screw = 668 N, Endobutton = 999 N and Bollard = 1153 N. Under cyclic loading conditions the titanium and bioabsorbable RCI screws rapidly failed after several hundred 5 to 150 N cycles due to tendon damage and slippage. Both the Bollards and Endobuttons survived 1500 cycles at 50-450N, with less tendon slippage. Conclusion: Titanium and bioabsorbale RCI screws provide poor initial fixation of tendon grafts and fail rapidly under cyclic loading. Both Bollards and Endobuttons provide sufficiently high UTL’s and survive cyclic loading to allow early postoperative rehabilitation.