Vastus lateralis/vastus medialis cross-sectional area ratio impacts presence and degree of knee joint abnormalities and cartilage T2 determined with 3T MRI – an analysis from the incidence cohort of the Osteoarthritis Initiative

Summary Objective To study the role of vastus lateralis/vastus medialis cross-sectional area CSA ratio (VL/VM CSA ratio) in preclinical knee osteoarthritis (OA) using magnetic resonance imaging (MRI)-based cartilage T2 mapping technique and morphological analysis at 3.0T in non-symptomatic, middle-aged subjects. Material and methods 174 non-symptomatic individuals aged 45–55 years with OA risk factors were selected from the Osteoarthritis Initiative (OAI) incidence cohort. OA-related knee abnormalities were analyzed using the whole-organ magnetic resonance imaging score (WORMS). Knee cartilage T2 maps were generated using sagittal 2D multi-echo spin-echo images of the right knee. CSA of thigh muscles was measured using axial T1W images of the right mid thigh. Spline-based segmentation of cartilage and muscles was performed on a SUN/SPARC workstation. Muscle measurements were normalized to body size using body surface area (BSA). Statistical significance was determined using Student’s t -test, Pearson correlation test, and multiple regression models. To correct for multiple testing, Bonferroni adjustments were applied across all tests within each of the primary results tables ( Tables III–VII ). Results Higher T2 values were associated with increased prevalence and severity of cartilage degeneration. In our study, male and female subjects with higher VL/VM CSA ratio demonstrated significantly lower mean cartilage T2 values (all compartments combined) (mean 44.10 vs 45.17, P = 0.0017), and significantly lower WORMS scores (mean 14.12 vs 18.68, P = 0.0316). Regression analyses of combined mean cartilage T2 using VL/VM CSA ratio as a continuous predictor showed a significant curvilinear relationship between these two variables ( P = 0.0082). Conclusion Our results suggested that higher VL/VM CSA ratio is associated with lower T2 values and decreased presence and severity of OA-related morphological changes. Additional studies will be needed to determine causality.