Effect Of Ankle Plantar Flexion On ACL Strain During Landing From A Jump

Abstract

Injuries to the Anterior Cruciate Ligament (ACL) are one of the most common injuries in athletic activities. Landing from a jump is one of the leading athletic activities associated with ACL injuries. Researchers have postulated that landing flat footed (hill contact) is a more detrimental landing posture to ACL health than landing on toes (or ball of foot). In this research, a novel hybrid robotic system utilizing cadaveric legs (six inches above the knee joint to the toes) was designed to simulate lower extremity biomechanics. The robotic system has the ability to raise a cadaveric leg with pre-applied muscle forces and instrumented ACL to a desired height and drop it onto a force plate. Because we have full access to the foot and ankle joint, tests were performed to determine the impact of flat footed versus plantar flexed landing at various hip and knee flexion angles. PURPOSE: To compare the strain of the ACL during a one inch jump landing with foot in a toe down, plantar flexion position verses flat footed, with foot parallel to contact surface. METHODS: Four cadaveric knees were tested using a hybrid biomechanical device designed to simulate athletic activities such as landing from a jump, or a plant and cut movement. The cadaveric knees were attached to the device by insertion of a threaded rod implanted into the femur. Quadriceps and Hamstring (Q/H) forces were applied by the use of linear pull cables attached to the associated muscle group. Hip flexion angle was controlled allowing comparison of ACL strain at different degrees of hip flexion during flat-footed and plantar flexed landing scenarios. ACL deformation, Ground Reaction Force (GRF), Q/H forces, and Hip Flexion/Extension were measured across all tests. Data was post-processed using MATLAB to find maximum GRF, ACL deformation during impact, and associated muscle forces. T tests were performed comparing ACL strain of flat-footed vs. plantar-flexed landings. RESULTS: ACL strain of flat footed landings at all hip flexion angles were significantly higher than the plantar flexed tests (p = 0.0019). CONCLUSION: Our results indicate that landing from a jump with the foot plantar flexed lowers the strain on the ACL compared to a flat footed jump landing. The main reason for this could be the shock absorbing role of the ankle and foot ligaments during the plantar flexed landings.