Quadriceps strength and corticospinal excitability as predictors of disability after anterior cruciate ligament reconstruction.

BACKGROUND: Disability is common in a proportion of patients after anterior cruciate ligament reconstruction (ACL-R). Neuromuscular quadriceps deficits are a hallmark impairment after ACL-R, yet the link between muscle function and disability is not understood. PURPOSES: To evaluate the ability of quadriceps strength and cortical excitability to predict self-reported disability in patients with ACL-R.
METHODS: Fifteen participants with a history of ACL-R (11 female, 4 male; 172 ± 9.8 cm, 70.4 ± 17.5 kg, 54.4 ± 40.9 mo postsurgery) were included in this study. Corticospinal excitability was assessed using active motor thresholds (AMT), while strength was assessed with maximal voluntary isometric contractions (MVIC). Both voluntary strength and corticospinal excitability were used to predict disability measured with the International Knee Documentation Committee Index (IKDC).
RESULTS: The overall multiple-regression model significantly predicted 66% of the variance in self-reported disability as measured by the IKDC index (R2 = .66, P = .01). Initial imputation of MVIC into the model accounted for 61% (R2 = .61, P = .01) of the variance in IKDC. The subsequent addition of AMT into the model accounted for an insignificant increase of 5% (Δ R2 = .05, P = .19) in the prediction capability of the model.
CONCLUSIONS: Quadriceps voluntary strength and cortical excitability predicted two-thirds of the variance in disability of patients with ACL-R, with strength accounting for virtually all of the predictive capability of the model.