Where should the femoral tunnel of a posterior cruciate ligament reconstruction be placed to best restore anteroposterior laxity and ligament forces?

Background: Objective results of posterior cruciate ligament reconstruction are often less than satisfactory, with many patients exhibiting excessive posterior laxity. Hypothesis: Changes in the position of the femoral tunnel within the posterior cruciate ligament's femoral footprint will significantly affect anteroposterior laxities and graft forces. Study Design: Controlled laboratory study. Methods: The posterior cruciate ligament's femoral origin was mechanically isolated in 13 fresh-frozen knee specimens, and the bone cap containing the ligament's insertion was attached to a load cell that recorded resultant force during tibial loading tests. Anteroposterior laxity (at +/- 200 N applied force) was also measured. Cast acrylic replicas of the bone cap were fabricated, with tunnels placed in anterolateral, central, and posteromedial regions of the footprint. A graft reconstruction was tested in each tunnel. Results: Mean laxities with the anterolateral tunnel were +0.9 mm to +1.7 mm greater than normal between 0 degrees and 45 degrees of flexion. Mean laxities with the posteromedial tunnel were -2.4 mm to -3.7 mm less than normal between 10 degrees and 45 degrees of flexion. Mean laxities with the central tunnel were not significantly different from intact knee values, except at 0 degrees (0.9 mm greater). Mean graft forces with the anterolateral tunnel were normal for most modes of loading, whereas there were significant increases in graft forces with the posteromedial and central tunnels. Conclusion: The anterolateral tunnel reproduced normal posterior cruciate ligament force profiles but produced a knee that was more lax than normal between 0 degrees and 45 degrees of flexion. The central tunnel best matched intact knee laxities, but graft forces were higher than posterior cruciate ligament forces between 0 degrees and 45 degrees of flexion. The posteromedial tunnel overconstrained anteroposterior laxity approximately 2 to 4 mm between 0 degrees and 45 degrees of flexion and generated higher graft forces in the same flexion range. Clinical Relevance: This study suggests that a posteromedial tunnel should not be used for single-bundle posterior cruciate ligament reconstruction.