Biomechanical Evaluation of Anterior Cruciate Ligament Femoral Fixation Techniques

Background: A number of different femoral anterior cruciate ligament fixation techniques are currently in use. Slippage of the graft caused by excessive early loading or aggressive rehabilitation may negate benefits of surgery and result in a knee with undesirable laxity. Hypothesis: Anterior cruciate ligament femoral graft slippage varies by fixation technique and amount of cyclic loading. Study Design: Controlled laboratory study. Methods: Graft slippage in 5 different soft tissue anterior cruciate ligament femoral fixation techniques (Bio-TransFix cross-pin technique, Stratis ST cross-pin technique, Bilok ST transverse femoral screw, Delta tapered bio-interference screw, and single-loop TensionLok) was compared by cyclic loading of double-bundle grafts in porcine femurs. Graft slippage was measured using a differential variable reluctance transducer. Results: The Bio-TransFix had significantly less (P = .002) total graft slippage (1.14 +/- 0.43 mm) compared to the Delta (3.74 +/- 3.25 mm), Bilok ST (3.92 +/- 2.28 mm), and TensionLok (5.09 +/- 1.12 mm) but not the Stratis ST (1.92 +/- 1.55 mm). All techniques showed the greatest amount of dynamic excursion (P < .001), slippage (P < .001), and percentage of total slippage (mean 68%, P < .001) during the first 100 cycles of loading. The TensionLok had the greatest amount of dynamic excursion during the first 100 cycles (4.15 +/- 1.00 mm) followed by the Bilok ST (3.37 +/- 2.07 mm), Delta (1.76 +/- 0.93 mm), and Stratis ST (1.75 +/- 0.96 mm); the Bio-TransFix demonstrated the least (1.26 +/- 0.48 mm). There was no statistical difference in failure load between repair techniques (P = .103). Conclusion: Graft slippage was statistically different between anterior cruciate ligament femoral fixation techniques for static and dynamic loading. All techniques exhibited the greatest amount of slippage during the first 100 cycles of loading. The differential variable reluctance transducer permitted evaluation of dynamic graft-construct-bone displacement during experimental loading, simulating the loading experienced during early rehabilitation. Clinical Relevance: The optimal method of graft fixation for anterior cruciate ligament reconstruction remains unknown. In the current study, cross-pin constructs appeared to be superior to certain other available fixation systems.