Biomechanical contributors to loading rates during gait following anterior cruciate ligament reconstruction

Post-traumatic knee osteoarthritis (PTOA) develops rapidly after anterior cruciate ligament reconstruction (ACLR) and both high and low vertical ground reaction force (vGRF) loading rates are associated with cartilage degeneration. However, the gait characteristics that influence vGRF linear and instantaneous loading rates after ACLR are unknown. Sixty-nine individuals with ACLR (sex: 72 % female, age: 20 ± 3 years, and time since ACLR: 26 ± 16 months) walked at a self-selected pace from which the vGRF linear (slope from heel strike to peak) and instantaneous (peak of the first time derivative) loading rates were calculated. Lasso regressions were utilized to objectively identify a subset of predictor variables that influence vGRF linear and instantaneous loading rates. The identified predictors were then utilized in multiple regressions to determine the unique variance attributable to each predictor by computing ${\Delta r}^2$ when that predictor was removed from the model. Greater gait speed (${\Delta r}^2=0.019)$, greater medial hamstring preparatory amplitude (${\Delta r}^2=0.022)$, and lesser peak posterior ground reaction force (pGRF) (${\Delta r}^2=0.103)$ were associated with greater vGRF linear loading rate. Greater gait speed (${\Delta r}^2=0.072)$, greater medial hamstring preparatory amplitude ($\Delta$ r² = 0.016), greater anterior ground reaction force (aGRF) immediately after heel strike (${\Delta r}^2=0.054)$, and lesser peak pGRF (${\Delta r}^2=0.019)$ were associated with greater vGRF instantaneous loading rates. Lesser pGRF and greater aGRF immediately after heel strike explain additional variance in vGRF linear and instantaneous loading rates beyond that explained by gait speed. Future investigations should evaluate the relationship between the aGRF immediately after heel strike and pGRF with indicators of cartilage degeneration.