An examination of possible quadriceps force at the time of anterior cruciate ligament injury during landing: A simulation study.

Anterior cruciate ligament (ACL) rupture is a common and traumatic injury. Although, identifying the mechanism of ACL injury has received considerable research attention, there are still many unanswered questions. One proposed mechanism asserts that the ACL is injured due to an aggressive quadriceps muscle contraction. However, recently it has been questioned if the magnitude of quadriceps force needed to tear the ACL is physiologically realistic under the conditions where injury occurs during landing (e.g. near full knee extension and within 50ms after impact). To answer this question, a simple simulation model was developed to examine the upper bounds of quadriceps force that can be developed under these conditions. The model included force-length, and force-velocity properties as well as activation dynamics. Model parameters were chosen to provide a high estimate for possible quadriceps force in a young healthy man. The effects of varying quadriceps pre-activation levels were also examined. When using realistic pre-activation levels, the simulated quadriceps force was less than half of what has been shown to cause ACL injury. Even when using maximum pre-activation, the quadriceps force still did not reach close to the level shown to cause injury. Therefore, we conclude that quadriceps force alone seems to be an unlikely mechanism for ACL injury.