The Relationship Between Anterior Tibial Acceleration, Tibial Slope, and ACL Strain During a Simulated Jump Landing Task

Background Knee joint morphology contributions to anterior cruciate ligament (ACL) loading are rarely considered in the injury prevention model. This may be problematic as the knee mechanical response may be influenced by these underlying morphological factors. The goal of the present study was to explore the relationship between posterior tibial slope (which has been recently postulated to influence knee and ACL loading), impact-induced anterior tibial acceleration, and resultant ACL strain during a simulated single-leg landing. Methods Eleven lower limb cadaveric specimens from female donors who had had a mean age (and standard deviation) of 65 ± 10.5 years at the time of death were mounted in a testing apparatus to simulate single-limb landings in the presence of pre-impact knee muscle forces. After preconditioning, specimens underwent five impact trials (mean impact force, 1297.9 ± 210.6 N) while synchronous three-dimensional joint kinetics, kinematics, and relative anteromedial bundle strain data were recorded. Mean peak tibial acceleration and anteromedial bundle strain were quantified over the first 200 ms after impact. These values, along with radiographically defined posterior tibial slope measurements, were submitted to individual and stepwise linear regression analyses. Results The mean peak anteromedial bundle strain (3.35% ± 1.71%) was significantly correlated (r = 0.79; p = 0.004; β = 0.791) with anterior tibial acceleration (8.31 ± 2.77 m/s−2 ), with the times to respective peaks (66 ± 7 ms and 66 ± 4 ms) also being significantly correlated (r = 0.82; p = 0.001; β = 0.818). Posterior tibial slope (mean, 7.6° ± 2.1°) was significantly correlated with both peak anterior tibial acceleration (r = 0.75; p = 0.004; β = 0.786) and peak anteromedial bundle strain (r = 0.76; p = 0.007; β = 0.759). Conclusions Impact-induced ACL strain is directly proportional to anterior tibial acceleration, with this relationship being moderately dependent on the posterior slope of the tibial plateau. Clinical Relevance Anterior tibial acceleration is associated with anteromedial bundle strain during simulated landings. The magnitude of the impact-induced accelerations governing the strain response is additionally correlated with the posterior slope of the tibial plateau. Additional exploration of the effect of other knee morphological variables on ACL strain during simulated high-risk landings appears warranted.