Associations of medial collateral ligament and cartilage thickness with clinical outcomes in medial knee osteoarthritis: a cross-sectional study.

objectiveThe aim of this study was to evaluate the thickness of the medial collateral ligament (MCL) sonographically in individuals with medial compartment knee osteoarthritis and to investigate its relationship with femoral cartilage thickness, pain, and functional status.

methodsThis cross-sectional study included 21 patients diagnosed with medial compartment knee osteoarthritis radiologically (Kellgren-Lawrence grade 2 or 3) and 21 age- and sex-matched healthy individuals. MCL thickness was measured using ultrasonography approximately 1 cm proximal and 1 cm distal to the medial joint line. Femoral cartilage thickness was assessed at the medial condyle, intercondylar area, and lateral condyle. Pain levels were evaluated using the Visual Analog Scale (VAS), and functional status was assessed using the KOOS-PS (Knee Injury and Osteoarthritis Outcome Score-Physical Function Shortform).

resultsProximal MCL thickness was significantly greater in the osteoarthritis group compared to the control group (2.0 ± 0.3 mm vs. 1.6 ± 0.2 mm, p < 0.001); distal MCL thickness was also significantly increased (1.5 ± 0.2 mm vs. 1.2 ± 0.1 mm, p = 0.002). Femoral cartilage thickness was significantly lower in patients with osteoarthritis than in healthy controls at the medial condyle (0.21 ± 0.03 cm vs. 0.26 ± 0.02 cm, p < 0.001), intercondylar area (0.25 ± 0.03 cm vs. 0.29 ± 0.02 cm, p < 0.001), and lateral condyle (0.21 ± 0.04 cm vs. 0.25 ± 0.03 cm, p = 0.005). A weak negative correlation was found between proximal MCL thickness and both medial (rho = -0.360, p = 0.022) and intercondylar (rho = -0.373, p = 0.018) cartilage thickness. A moderate negative correlation was observed between both proximal (rho = -0.523, p = 0.001) and distal (rho = -0.587, p < 0.001) MCL thicknesses and KOOS-PS scores.

conclusionMCL thickness increases in medial knee osteoarthritis, and this thickening is negatively associated with both cartilage thickness and functional status. These findings suggest that the degeneration process in medial knee osteoarthritis is not limited to cartilage alone; surrounding soft tissue structures such as the MCL may also be affected. Careful sonographic examination of the MCL will contribute to a more optimal evaluation of this patient group. Key Points • This is the first study to evaluate medial collateral ligament (MCL) thickness sonographically in patients with medial knee osteoarthritis. • MCL thickness was significantly increased in osteoarthritis patients and negatively correlated with both femoral cartilage thickness and functional status. • Findings suggest that osteoarthritis affects not only cartilage but also periarticular soft tissues such as the MCL. • Sonographic assessment of the MCL may provide additional insights for diagnosis and management of medial knee osteoarthritis.