Cruciate injury patterns in knee hyperextension: a cadaveric model.

We created an experimental model to evaluate the effects of strain rate on the mechanism of combined cruciate ligament injuries in knee hyperextension. Using straight knee hyperextension to rupture the anterior and posterior cruciates, two strain rates (approximately 100% per second and 5400% per second) were applied to reproduce two clinical injury patterns of the knee: low energy (sporting) and high energy (pedestrian-motor vehicle accident). Ten pairs of fresh-frozen cadaveric knees were injured to 45 degrees of hyperextension. Strain rate sensitivity of the posterior cruciate ligament was shown in this model, with midsubstance tears occuring in specimens tested at a low rate and avulsion "stripping" injuries from the femoral side occuring at a high rate. A variable pattern of anterior cruciate ligament tears at both high and low rates suggests that the specific injury mechanism may also involve other factors including notch morphology. We present a simplified mathematic model used to estimate posterior cruciate ligament strain during knee hyperextension.