Side-to-side asymmetries in landing mechanics from a drop vertical jump test are not related to asymmetries in knee joint laxity following anterior cruciate ligament reconstruction

Purpose: Asymmetries in knee joint biomechanics and increased knee joint laxity in patients following anterior cruciate ligament reconstruction (ACLR) are considered risk factors for re-tear or early onset of osteoarthritis. Nevertheless, the relationship between these factors has not been established. The aim of the study was to compare knee mechanics during landing from a bilateral drop vertical jump in patients following ACLR and control participants and to study the relationship between side-to-side asymmetries in landing mechanics and knee joint laxity. Methods: Seventeen patients following ACLR were evaluated and compared to 28 healthy controls. Knee sagittal and frontal plane kinematics and kinetics were evaluated using three-dimensional motion capture (200 Hz) and two synchronized force platforms (1000 Hz). Static anterior and internal rotation knee laxities were measured for both groups and legs using dedicated arthrometers. Group and leg differences were investigated using a mixed model analysis of variance. The relationship between side-to-side differences in sagittal knee power/energy absorption and knee joint laxities was evaluated using univariate linear regression. Results: A significant group-by-leg interaction (p = 0.010) was found for knee sagittal plane energy absorption, with patients having 25% lower values in their involved compared to their non-involved leg (1.22 ± 0.39 vs. 1.62 ± 0.40 J kg⁻¹). Furthermore, knee sagittal plane energy absorption was 18% lower at their involved leg compared to controls (p = 0.018). Concomitantly, patients demonstrated a 27% higher anterior laxity of the involved knee compared to the non-involved knee, with an average side-to-side difference of 1.2 mm (p < 0.001). Laxity of the involved knee was also 30% higher than that of controls (p < 0.001) (leg-by-group interaction: p = 0.002). No relationship was found between sagittal plane energy absorption and knee laxity. Conclusions: Nine months following surgery, ACLR patients were shown to employ a knee unloading strategy of their involved leg during bilateral landing. However, this strategy was unrelated to their increased anterior knee laxity. Side-to-side asymmetries during simple bilateral landing tasks may put ACLR patients at increased risk of second ACL injury or early-onset osteoarthritis development. Detecting and correcting asymmetric landing strategies is highly relevant in the framework of personalized rehabilitation, which calls for complex biomechanical analyses to be applied in clinical routine. Level of evidence: III.