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

Abstract

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.