Bone Density and Insertion Torque as Predictors of Anterior Cruciateligament Graft Fixation Strength

Abstract

Background Bone mineral density and interference screw insertion torque are thought to be useful predictors of anterior cruciate ligament graft fixation strength. Hypothesis Bone mineral density and insertion torque are reliable predictors of anterior cruciate ligament graft fixation strength. Study Design Randomized experimental study. Methods The volumetric bone mineral density, maximum insertion torque, and initial fixation strength (determined both as cyclic-loading-induced displacement and yield load) were recorded on 21 pairs of anterior cruciate ligament reconstructions. To assess the accuracy of bone mineral density and insertion torque in predicting the fixation strength, half of the specimens were first used to determine the regression equations between the variables, and then the data from the remaining specimens were used to validate the prediction equations. Results Despite the relatively high group correlations, the ability of bone mineral density and insertion torque to predict the strength of graft fixation was poor. Errors ranging from –150% to 92%, –22% to 50%, –56% to 121%, and –23% to 50% were observed when bone mineral density and insertion torque were used to predict individual cyclic-loading-induced displacement and yield load, respectively. Conclusions Neither bone mineral density nor insertion torque provides a sufficiently accurate prediction of the fixation strength of an individual soft tissue anterior cruciate ligament graft. Clinical Relevance Bone mineral density and insertion torque cannot be used to estimate the strength of interference screw fixation in anterior cruciate ligament reconstruction.