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

J Orthop Sci. 2026 Mar 19:S0949-2658(26)00082-5. doi: 10.1016/j.jos.2026.02.015. Online ahead of print.

ABSTRACT

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 (MT_rest) and at maximal voluntary isometric contraction (MT_contraction), the velocity from rest state to maximum contraction (Velocity_activation) and the velocity from maximal contraction to rest state (Velocity_relaxation) were obtained by M-mode ultrasound. Maximum flexor and extensor strength were measured using an isokinetic dynamometer, the gold-standard assessment tool.

RESULTS: MT_rest and MT_contraction were significantly correlated with extension strength, also showed correlations with flexion strength. Velocity_activation correlated significantly with both strength (extension: r = 0.742; flexion: r = 0.707). Velocity_activation, 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. Velocity_activation 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).

PMID:41862305 | DOI:10.1016/j.jos.2026.02.015