Evaluation of a simulated pivot shift test: a biomechanical study

PURPOSE: Double-bundle anterior cruciate reconstructions have led to an increased interest in quantifying anterolateral rotatory stability. The application of combined internal rotation and valgus torques to the knee can more nearly recreate the anterolateral subluxation that occurs in the pivot shift test in vitro compared to coupled internal rotation torque and anterior tibial loads. METHODS: Twelve non-paired cadaveric knees were biomechanically tested with the ACL intact and sectioned. For each test state, six-degree-of-freedom positional data were collected for two simulated pivot shift loads consisting of a 5-Nm internal rotation torque coupled with either a 10-Nm valgus torque or an 88 N anterior tibial load at 0°, 20°, 30°, 60°, and 90° of knee flexion. RESULTS: The coupled internal rotation and valgus torques produced a significant increase in anterolateral subluxation between the ACL intact and sectioned states at all tested angles except 90º (5.9 ± 0.4 mm at 0°, 4.3 ± 0.6 mm at 20°, 3.5 ± 0.6 mm at 30°, 2.1 ± 0.6 mm at 60°). The coupled internal rotation and an anterior tibial load produced significant increases between the ACL intact and sectioned states at all tested angles except 30º (5.4 ± 0.5 mm at 0°, 3.7 ± 0.5 mm at 20°, 2.1 ± 0.8 mm at 60°, 1.4 ± 0.3 mm at 90°). CONCLUSIONS: We found that the coupled internal rotation and valgus torques best recreated the anterolateral subluxation that occurs in the pivot shift in vitro. This study describes an anterolateral subluxation test for ACL integrity in the laboratory setting.