Variation In Response to Limb Loading Instruction on Knee Mechanics During Squatting in Early Recovery Following Anterior Cruciate Ligament Reconstruction.

Context: On average, individuals in early recovery following anterior cruciate ligament reconstruction (ACLr) improve limb loading symmetry (LLS) with instruction to equalize weight distribution between limbs during squats. However, the extent to which these instructions improve knee extensor loading symmetry (KLS) or reduce intra-limb compensations is not known.

Objective: Determine how limb loading instructions influence knee and intra-limb loading in individuals 3-4 months post-ACLr and to explore variations in responses across individuals.

Design: Controlled Laboratory study.

Setting: Research Laboratory.

Patients: Individuals 109.4 days (18.2 days) post-ACLr (n=20) and healthy matched controls (CTRL; n=19).

Intervention: Participants performed double limb squats in natural (N; no instruction) and instructed (IN; instruction to evenly distribute weight between limbs) conditions.

Main outcome measures: Between limb and knee loading symmetry were calculated as the ratio of vertical ground reaction force and knee extensor moment impulse, between surgical(Sx):matched and non-surgical(NSx):matched limbs (ACLr:control), respectively. Intra- limb hip/knee (H/K) extensor loading distribution was calculated in Sx:matched limbs.

Results: LLS (N: 0.86; IN: 0.93, P < 0.001; ES:0.83) and KLS (N: 0.54; IN: 0.62, P=0.007; ES:0.67) improved with instruction in the ACLr group with no change in CTRL. H/K ratio did not change for either group. K-means clustering, considering natural and change (natural- instructed) in LLS, KLS, and H/K ratio, described response to instruction across three clusters: 1) ACLr: n=3; CTRL: n=9, were symmetrical in both conditions, 2) ACLr: n=14, showed some improvement in symmetry, 3) ACLr: n=3, only improved LLS.

Conclusions: Average data suggests that weightbearing instruction improved LLS to within 7%, but a 38% knee loading deficit remained, and intra-limb compensation did not improve. Data- driven clusters indicate that three ACLr subjects were similar to controls, fourteen improved LLS, KLS and H/K distribution, and three only improved LLS with worsening KLS and H/K.