Variation of Anatomical and Physiological Parameters that Affect Estimates of ACL Loading During Drop Landing

BACKGROUND: Anterior cruciate ligament (ACL) loading during drop landing has been recently studied with a sagittal plane knee model developed by Kernozek and Ragan using mean anatomical and physiological parameters obtained from cadaveric and clinical data. It is unknown how estimates in ACL load may be altered due to variations in anatomical and physiological parameters used from other research. METHODS: Using the same model, these parameters were systematically varied, including: tibial slope, moment arms of the patellar tendon, hamstring, and gastrocnemius at the knee and ankle, patellar tendon and hamstring line of force, ACL stiffness, and nonlinear muscle activation parameters. To determine the sensitivity of the model to changes in these parameters, each was varied independently by ±5% and by ranges reported in the literature. Changes in maximum ACL load and shear force components of the patellar tendon, hamstring, and tibio-femoral contact force were calculated from drop landing data of 21 subjects. RESULTS: The variation in ACL load during drop landing from its nominal value was largest (-100% to 176%) when extremes in reported tibial slope values were utilized. Variation in the next most important parameter, patellar tendon line of force, affected ACL load by -72% to 88%. CONCLUSION: Variations in tibial slope and patellar tendon line of force had the greatest influence on estimated ACL loading during drop landing. Differences in these parameters between subjects may be just as important to ACL loading as the kinematic and kinetic performance differences observed in landing.