Poster 257: Deficits in Contralateral Limb Strength Can Overestimate Limb Symmetry Index after Anterior Cruciate Ligament Reconstruction

Objectives: Some literature suggests that strength deficits and functional impairment of the contralateral, uninjured leg exist following ACL injury. Given the emergence of these findings and the contralateral, uninjured limb frequently being used as a control for comparison to the operative extremity in return-to-play, limb symmetry assessments, the primary objective of this study was to evaluate whether the contralateral, un-injured limb represents a dynamic, rather than static, data point. Methods: 144 patients undergoing ACL reconstruction at a single institution by six fellowship-trained surgeons between March 2013 and August 2018 were evaluated. Patients completed a standard institutional Lower-Extremity Assessment Protocol (LEAP) testing at six and nine months postoperatively for objective evaluation of ipsilateral and contralateral limb flexion and extension strength and functional performance. Retrospective chart review was performed to determine demographic and operative factors. Extension strength, flexion strength, limb symmetry index (LSI), and hop tests of ipsilateral and contralateral limbs were compared between the six- and nine-month LEAP testing outcomes. Further sub-analysis of cohorts demonstrating less than and greater than 10% difference in contralateral limb flexion and extension strength was performed. Binary logistic regression was utilized to evaluate demographic and operative risk factors for developing differences in contralateral limb strength. Results: On average, contralateral limb flexion and extension strength increased between 2-4% between six and nine months postoperatively. However, the contralateral limb demonstrated a difference of > 10% percent in extension strength in 24% of patients and in flexion strength in 38% of patients [Table 1; Table 2]. The cohort with >10% difference had significantly weaker contralateral extension and flexion strength at six months compared to the cohort that demonstrated < 10% difference (Extension: 2.00 vs. 2.39 N·m/kg, p < 0.001; Flexion: 0.84 vs. 1.08 N·m/kg, p < 0.001), but similar ipsilateral limb performance [Table 1; Table 2]. Therefore, the >10% difference cohort had a significantly greater LSI at six months compared to the < 10% difference cohort (67.3% vs. 59.4%, p = 0.006) [Table 1; Table 2]. At nine months postoperatively there was no difference in contralateral extension strength and LSI between cohorts. No demographic or operative risk factors were identified that correlated with which patients demonstrated deficits in contralateral limb strength. Conclusions: Although the contralateral, non-operative limb provides a relatively stable control value with which strength metrics of the ipsilateral, operative limb may be compared after ACL reconstruction, a significant percentage of patients will also demonstrate deficits in flexion and extension strength of the contralateral limb. This can result in an over-estimation of normality of limb symmetry comparisons. There were no identifiable demographic or operative risk factors to help identify which patients may demonstrate greater deficits with flexion and extension in the contralateral limb. Comparison of the operative extremity to a patient’s own pre-injury measures or that of a large, population-based, matched, un-injured, control group may be more ideal. [Table: see text][Table: see text]