Enhanced echo intensity in vastus medialis is associated with worsening of functional disabilities and symptoms in patients with knee osteoarthritis: a 3-year longitudinal study

Background: Patients with knee osteoarthritis (OA) experience muscle quality loss, and is characterized by the enhanced echo intensity (EI) of the vastus medialis (VM) muscles and a high extracellular water-to-intracellular water (ECW/ICW) ratio of the thigh. No longitudinal study has investigated the association of muscle degeneration at baseline with the progression of functional disabilities and symptoms in patients with knee OA, with a focus on muscle quality measured as EI and ECW/ICW. This study aimed to elucidate the association between muscle degeneration and worsening of functional disabilities and symptoms in patients with knee OA over 3 years duration. Methods: : Thirty-three patients with knee OA who completed follow-up over 3 years were included in the analysis. The knee scoring system (KSS) was used to evaluate the functional abilities and symptoms. Based on the 3-year change in KSS scores, patients were classified into progressive or non-progressive groups. Muscle thickness (MT) and EI of the VM were determined using ultrasonography. The ECW/ICW ratio was measured using segmental-bioelectrical impedance spectroscopy. Multivariable logistic regression analyses were conducted with the groups as the dependent variables and VM-MT, VM-EI, and ECW/ICW ratio at baseline as independent variables, including potential confounders as the age, body mass index, radiographic OA severity, and baseline KSS scores. Results: : Thirteen (39.4%) patients showed progressive features. VM-EI at baseline, but not the VM-MT and ECW/ICW ratio, was significantly associated with the progression of functional disabilities (adjusted odds ratio [OR], 1.24; 95% confidence interval [CI], 1.03-1.50) and symptoms (adjusted OR, 1.13; 95% CI, 1.01-1.25). Conclusions: : The findings of the current study suggest that enhanced VM-EI was associated with worsening of functional disabilities and symptoms in patients with knee OA over a period of 3 years. Therefore, VM-EI, which can be easily determined using the ultrasound images in clinical settings, may be a useful indicator for predicting future dysfunction and symptomatic worsening in patients with knee OA.