Rectus femoris deformations on M-mode ultrasonography as a reliable indicator of muscle strength in individuals with knee osteoarthritis: A cross-sectional study.

BACKGROUND

Real-time ultrasound monitoring of muscle architecture changes during dynamic contractions is gaining traction as a practical tool for neuromuscular functional assessment.

PURPOSE: This study aimed to assess the muscle thickness (MT) and deformation velocity of rectus femoris (RF) for predicting muscle strength capacity, evaluating their predictive validity and clinical feasibility.

METHODS

Twenty-three elderly individuals with knee osteoarthritis (KOA) were examined. The thickness of the muscle at rest (MTrest) and at maximal voluntary isometric contraction (MTcontraction), the velocity from rest state to maximum contraction (Velocityactivation) and the velocity from maximal contraction to rest state (Velocityrelaxation) were obtained by M-mode ultrasound. Maximum flexor and extensor strength were measured using an isokinetic dynamometer, the gold-standard assessment tool.

RESULTS

MTrest and MTcontraction were significantly correlated with extension strength, also showed correlations with flexion strength. Velocityactivation correlated significantly with both strength (extension: r = 0.742; flexion: r = 0.707). Velocityactivation, but not MT, remained a statistically significant predictor of both extension and flexion strength in multivariate regression models (extension: adjusted R2 = 0.381; flexion: adjusted R2 = 0.314).

CONCLUSIONS

The deformation of RF, as measured by M-mode ultrasound, provides a visualization method for assessing extension and flexion strength. Velocityactivation showed a significant correlation with both extension and flexion strength. Furthermore, it improved the prediction of thigh muscle strength beyond muscle thickness (MT) alone. Assessing the deformation of RF by M-mode ultrasound may be valuable for detecting alterations in muscle strength and function throughout the disease process in individuals with knee osteoarthritis (KOA).