Kinematic and Kinetic Risk Factors Exist Bilaterally During the First and Second Landing of the Drop Vertical Jump in Adolescent Patients following ACL Reconstruction

Most anterior cruciate ligament (ACL) tears occur during non-contact, deceleration phases of sports activity. Injury risk screenings use the drop vertical jump (DVJ) to assess landing mechanisms, but no researchers have examined biomechanical differences between the first and second landings in youth athletes following ACL reconstruction. # Purpose The purpose of this study was to compare biomechanical risk factors in the first and second DVJ landings in both the surgical (affected) and unaffected limbs in youth athletes recently cleared for RTP following ACL reconstruction. # Study Design Cross Sectional # Methods A total of 58 youth athletes (37 females, 21 males; 15.9 ± 1.9 years; 164.0 ± 9.5 cm; 66.0 ± 15.3 kg) who had undergone ACL reconstruction (ACLR) and were granted return to play (RTP) clearance from their physician participated in this study between 2020 and 2024. Kinematic and kinetic data using 3-Dimensional motion capture were collected while participants performed a series of dynamic tasks which included a DVJ with standardized instructions. Wilcoxon signed-rank tests were performed to determine significant differences between the first (1st) and second (2nd) DVJ landings, as well as between the affected (AFF) and unaffected (UNAFF) limbs. Effect sizes (r) were computed for all significant comparisons. A Holm-Bonferroni correction was applied within each comparison group due to multiple comparisons. # Results There were greater biomechanical risk factors associated with dynamic knee valgus during the first landing, including knee valgus (AFF: p<0.001; UNAFF: p=0.001), hip internal rotation (AFF: p<0.001; UNAFF: p<0.001), knee external rotation (UNAFF: p<0.001). Overall, there were more significant biomechanical risk factors in the unaffected limb compared to the affected limb in both landings. A stiffer landing, with less trunk flexion (AFF: p<0.001; UNAFF: p<0.001), knee flexion (AFF: p<0.001; UNAFF: p<0.001), and hip flexion (AFF: p<0.001; UNAFF: p<0.001) was observed in the second landing. # Conclusion More biomechanical risk factors occurred during the first landing of the DVJ, with more risk factors present in the unaffected limb during both landings. These findings highlight the need for a comprehensive DVJ assessment of both landings and both limbs for evaluation of RTP readiness following ACL reconstruction. # Level of Evidence III.