Relationship Between Quadriceps Strength at 6 Months Postoperatively and Improvement in Patient-Reported Knee Function After Anterior Cruciate Ligament Reconstruction.

Background: Understanding the factors associated with poor recovery over time after anterior cruciate ligament reconstruction (ACLR) helps clinicians identify patients who are at risk and targets for an intervention.

Purpose: To determine the factors associated with improvement in subjective knee function from 6 to 12 months after ACLR.

Study Design: Case-control study; Level of evidence, 3.

Methods: A total of 91 patients undergoing primary unilateral ACLR were included. Subjective knee function was assessed using the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) at 6 and 12 months postoperatively. Isokinetic knee strength (quadriceps and hamstring) and Anterior Cruciate Ligament-Return to Sport After Injury (ACL-RSI) scale scores were also assessed. Patients were included in the poor recovery group if their improvement in the IKDC-SKF score from 6 to 12 months was <15.5 points (minimal detectable change) and their IKDC-SKF score at 12 months was <90 points (maximum, 100 points). The IKDC-SKF score, knee strength, and the ACL-RSI score were compared between the poor recovery and good recovery groups with and without propensity score matching. Matched variables included age, sex, and IKDC-SKF score at 6 months after ACLR. In addition, logistic regression analysis was performed to identify factors that discriminated between the poor recovery and good recovery groups.

Results: There were 32 participants (35%) allocated to the poor recovery group. Before propensity score matching, the poor recovery group had a significantly older age, lower IKDC-SKF scores at 6 and 12 months, and a lower limb symmetry index (LSI) for quadriceps strength at 6 months. After propensity score matching, the LSI for quadriceps strength at 6 months was significantly different between the poor recovery and good recovery groups (73.0 ± 17.4 vs 83.3 ± 18.2, respectively; = .039). Logistic regression analysis showed that a lower LSI for quadriceps strength at 6 months was significantly associated with poor recovery of the IKDC-SKF score (odds ratio, 0.96 [95% CI, 0.93-0.98]), and receiver operating characteristic curve analysis identified 80.9% as a cutoff value of the LSI for quadriceps strength with 75.0% sensitivity and 61.0% specificity.

Conclusion: A lower LSI for quadriceps strength at 6 months postoperatively was associated with poor recovery of the IKDC-SKF score from 6 to 12 months after ACLR, even after adjusting for confounders.