Biomechanical properties of different interference screw designs for anterior cruciate ligament reconstruction
Rothberg, Lindsay Morgan
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The site of failure in anterior cruciate ligament (ACL) reconstruction surgery typically occurs at the interface between the replacement graft and the fixation device. A fixation device used in this type of surgery is an interference screw. Interference screws come in a variety of material compositions, sizes and shapes. This experiment was undertaken to compare the biomechanical properties of three different interference screws (BioComposite Full Thread, BioComposite Delta Tapered, and Soft Screw; Arthrex, Naples, FL). A novel technique, created in a prior study , was used to measure interference screw displacement throughout the entire length of the experiment which has not been done in previous tests. Porcine femurs and bovine extensor tendons were used to perform the 27 ACL reconstruction surgeries (9 samples/screw type). A load controlled actuator and a motion capturing system were used throughout conditioning, cyclic loading, and load to failure tests. By continuously capturing data, movement of the interference screws and tendons were seen throughout the entire test. Failure of the fixation was due to either slipping of the tendon or tearing of the tendon. Significant differences were seen in the ultimate loads of the metal screw (615.60 ± 83.56 N) and delta-tapered screw (795.91±85.36 N) (p=0.001). Significant differences were also seen in the amount of tendon elongation after cyclic loading between the full thread (3.39 ± 0.83 mm) and delta-tapered screws (2.42 ± 0.65 mm) (p=0.038). No significant differences were seen in the displacement of the interference screw, the stiffness, or the yield load. The stiffness of the reconstructed ACL construct happens to be one of the more important qualities needed for a good graft fixation. Being that there was no significant difference in stiffness, it has been concluded that out of these 3 designs, one design was not better then the others.