Association of Loading Asymmetry During Squatting With Loading Asymmetry During Drop Jump After ACL Reconstruction: Implications for Rehabilitation Progression.

BACKGROUND

Biomechanical asymmetries after anterior cruciate ligament reconstruction (ACLR) may be amplified and perpetuated by progressing athletes to higher-demand tasks despite impairments in lower-demand tasks.

HYPOTHESES: (1) Between-limb asymmetries in limb loading and joint kinetics will be greater during the higher-demand drop jump compared with squatting. (2) Asymmetries in limb loading and joint kinetics during squatting will be associated with asymmetries during drop jump.

STUDY

DESIGN

Descriptive laboratory study.

LEVEL OF EVIDENCE: Level 4.

METHODS

A total of 22 (11 female) participants after primary ACLR (6.4 ± 0.5 months) performed bilateral squat and drop jump tasks. Vertical ground-reaction force (vGRF), knee and hip extensor net joint moments (NJMs), hip/knee mean NJM ratio, and limb symmetry index (LSI) were calculated during the eccentric phase. Comparisons between limbs and across tasks were analyzed using 2-way repeated measures analyses of variance. Pearson's correlations assessed associations between vGRF and NJM LSIs, and hip/knee NJM ratios across tasks.

RESULTS

Mean vGRF LSI and knee NJM LSI were significantly more asymmetric during drop jump compared with squatting (79.7 ± 14.9 vs 90.0 ± 11.0%, P < 0.001 and 55.8 ± 17.6 vs 66.4 ± 25.6%, P = 0.02, respectively). Mean vGRF LSI (r = 0.58; P = 0.004) and knee NJM LSI (r = 0.61; P = 0.002) were moderately correlated between tasks. The hip/knee ratio for the ACLR limb correlated strongly between tasks (r = 0.69; P < 0.001); nonsurgical limb: r = 0.39; P = 0.07).

CONCLUSION

Underloading and reduced functional use of the ACLR knee were amplified during the drop jump compared with squatting. Limb mechanics during lower-demand squatting are informative of performance during drop jump.

CLINICAL RELEVANCE: Criterion-based rehabilitation guidelines may benefit from requiring symmetry in lower-demand tasks before progressing to higher-level activities to optimize recovery and reduce risk of reinjury.