Comparison Of Limb Symmetry Calculation Approaches For Assessing Muscle Function After Acl Reconstruction

PURPOSE: To determine the relationship between three limb symmetry methods and patient-reported outcomes (PROs) in patients less than 9 months post-ACL reconstruction as limb symmetry and PROs are widely used in clinical settings to determine a patient’s readiness to return to sport after ACL reconstruction. METHODS: 39 patients with a primary, uncomplicated ACL reconstruction (Age: 30.6 ± 12.4 years; Height; 1.7 ± 0.2 m; Mass: 80.8 ± 24.9 kg; Time since surgery: 5.6 ± 1.6 mo) participated in a single session evaluation that assessed knee extensor strength and subjective knee function (IKDC and KOOS-QOL). Bilateral maximal isokinetic knee extension torque was assessed using a dynamometer at a concentric mode at 120°/s. Six trials were performed and the middle 4 trials were used for analysis for each limb. Limb symmetry index (LSI) was calculated as peak torque of the involved limb divided by peak torque of the uninvolved limb. Normalized limb symmetry (NSI) was calculated for each trial and averaged. LSI sum (LSI’) was calculated as the peak torque value of the involved limb divided by the sum of the peak torque of both limbs. We used t-tests and correlation coefficients to identify relationships between the different LSI approaches and subjective knee function. RESULTS: All three LSI methods were significantly different from each other (p=<0.001). There was a significant moderate correlation between KOOS-QOL and NSI (p=0.013), KOOS-QOL and LSI (p=0.007), KOOS-QOL and LSI sum (p=0.005), IKDC and NSI (p=0.003), IKDC and LSI (p=0.001), and IKDC and LSI sum (p=0.001). CONCLUSION: Despite the significant differences between each approach to calculating LSI, all three methods similarly relate to PROs, thus PROs may not be indicative of quadriceps strength symmetry. Clinicians should take caution in choosing which method is best suitable when using isokinetic strength symmetry as a return to sport criteria due to the significant differences between each approach. - *Means are significantly different at <.05. **Correlation coefficient is significant at <.05