Relationship Between Quadriceps Strength at 6 Months Postoperatively and Improvement in Patient-Reported Knee...

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.

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

Case-control study; Level of evidence, 3.

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.

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; P = .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.

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.