Task dependent early landing kinematics after return to sport in individuals with ACL reconstruction: a secondary...

Despite returning to sport (RTS), individuals after anterior cruciate ligament reconstruction (ACLR) may exhibit residual biomechanical alterations that are not fully captured by conventional RTS assessments. This study investigated 3D lower-limb kinematics during the critical early landing phase (0-100 ms) in individuals who had already returned to sport after ACLR, with the aim of examining how task-specific demands and localized acute fatigue influence early landing movement patterns.

In this secondary analysis of a publicly available 3D motion capture dataset, 19 participants post ACLR (involved limb) and 22 healthy controls (dominant limb) were assessed. Knee, ankle, and pelvic joint angles were extracted at initial contact (IC, 0 ms) and at 25, 50, 75, and 100 ms intervals. Tasks included the unilateral counter movement jump (uCMJ) and single leg forward hop (SLH) under fatigued and non-fatigued conditions. Linear mixed-effects models compared kinematics across groups and conditions.

The ACLR group demonstrated a consistent transverse plane kinematic pattern suggestive of greater knee internal rotation during the early landing phase across all tasks (p < 0.05). Sagittal plane strategies showed marked task dependency. During the SLH task, the ACLR group showed a stiffer landing pattern, characterized by reduced knee flexion by 2°-4° and concurrent ankle dorsiflexion restriction around 50 ms after IC. Conversely, no significant between-group differences in knee flexion were observed during the uCMJ task. Furthermore, the localized acute fatigue protocol did not significantly alter these observed inter-group discrepancies.

Individuals who had returned to sport after ACLR may retain residual early landing kinematic patterns, including a consistent transverse plane movement pattern and task specific stiff landing strategies. Future RTS assessment and post-RTS monitoring may benefit from placing greater emphasis on tasks with substantial horizontal braking demands, such as the SLH, as these tasks may provide additional information on residual early landing movement control patterns beyond conventional performance based outcomes. Rehabilitation may benefit from targeting landing quality, rotational control, and distal ankle buffering capacity.