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

CONTEXT

On average, individuals in early recovery after 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 intralimb compensations is not known.

OBJECTIVES

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

DESIGN

Controlled laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

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 (no instruction) and instructed (instruction to evenly distribute weight between limbs) conditions.

MAIN OUTCOME MEASURE(S): Between-limbs and KLS were calculated as the ratio of vertical ground reaction force and knee extensor moment impulse, between surgical (Sx) : matched and nonsurgical (NSx) : matched limbs (ACLr : CTRL), respectively. Intralimb hip/knee (H/K) extensor loading distribution was calculated in Sx : matched limbs.

RESULTS

Limb loading symmetry (natural = 0.86; instructed = 0.93, P < .001; effect size = 0.83) and KLS (natural = 0.54; instructed = 0.62, P = .007; effect size = 0.67) improved with instruction in the ACLr group with no change in the CTRL group. Hip/knee ratio did not change for either group. Here, k-means clustering, considering natural and change (natural-instructed) in LLS, KLS, and H/K ratio, described the response to instruction across 3 clusters: (1) ACLr: n = 3; CTRL: n = 9, were symmetrical in both conditions; (2) ACLr: n = 14, showed some improvement in symmetry, and (3) ACLr: n = 3, only improved LLS.

CONCLUSIONS

Average data suggest that weightbearing instruction improved LLS to within 7%, but a 38% knee loading deficit remained, and intralimb compensation did not improve. Data-driven clusters indicate that 3 ACLr participants were similar to CTRLs; 14 improved LLS, KLS, and H/K distribution; and 3 only improved LLS with worsening KLS and H/K.