Use of the Uninvolved Limb as Comparator When Calculating Return to Sports Hop Test Symmetry After ACL Reconstruction

Horizontal hop testing is a reliable measure included in test batteries after anterior cruciate ligament (ACL) reconstruction (ACLR). Hop test results are typically expressed as limb symmetry indexes (LSIs) comparing the involved limb with the uninvolved limb. Using the uninvolved limb as a comparative measure has been questioned due to concerns that performance may be reduced in this limb also and may not be a stable comparison across time, leading to a falsely inflated LSI. Here, we report changes in uninvolved limb hop scores over 5 timepoints after ACLR.

Uninvolved limb hop scores would be similar between preoperative rehabilitation and 2 years after ACLR.

Cohort study.

Level III.

Level I and II athletes were enrolled after isolated ACL injury. Participants completed a preoperative hop testing battery after impairment resolution, preoperative rehabilitation, and 6 months, 1 year, and 2 years after ACLR. Linear mixed-effects models were performed separately for each hop and each limb to characterize change in scores over time. Pairwise comparisons for fixed effects of timepoint and estimated marginal means are reported.

A total of 182 athletes (25.0 ± 8.8 years, 44% female) were enrolled a mean of 54 days from ACL injury. For each hop, the uninvolved limb hop distance was statistically different from the impairment resolution timepoint only to various follow-up timepoints (P ≤ 0.009). If athletes underwent preoperative rehabilitation, uninvolved limb hop distance was stable throughout the duration of rehabilitation until 2 years, apart from timed hop from 6 months to 2 years (P = 0.04).

The uninvolved limb is a stable comparison for calculating hop test LSIs as part of return-to-sport decisions.

These results increase confidence in using symmetry as an outcome and are important for clinicians lacking preinjury hop testing data.