BACKGROUND: Joint space narrowing on plain radiographs has long been used as a proxy for the degree of knee osteoarthritis (OA). More recently, the utility of different quantitative MRI (qMRI) techniques measurements of cartilage morphology have been shown to be more responsive to knee OA progression.
OBJECTIVE: To evaluate how demographic variables and meniscus damage influence the degree of cartilage loss assessed by qMRI longitudinally, and whether cartilage loss correlates with pain outcome scores.
METHODS: Of 4,796 participants in the Osteoarthritis Initiative (OAI), a subset of 86 had baseline and 48 month follow-up qMRI medial femorotibial cartilage thickness data and were included in the study. The 86 subjects had a mean age of 59.9 years (range 45-79 years), were 48% male, and had mean baseline BMI 29.7 (range 18-46). Other variables included baseline meniscus pathology, and Knee Injury and Osteoarthritis Outcome Score (KOOS) Outcomes measures (baseline and 72 months). A musculoskeletal radiologist evaluated meniscus pathology on baseline MRIs; menisci were assigned Whole-Organ Magnetic Resonance Imaging Score (WORMS) scores, and graded on degree of meniscal extrusion on each knee included in the study.
RESULTS: Mean cartilage loss for the 86 subject cohort was 0.074 mm (range -0.08 to 0.43mm, p<0.0001, paired t-test). Cartilage loss correlated poorly with age (Pearson r=0.24) and had no association with gender (male mean 0.085, female mean 0.063, p=0.27, Wilcoxon rank sum). Baseline WORMS score, when dichotomized to ≤2 (n=44) and >3 (n=42), was found to be a significant predictor of longitudindal cartilage loss (p=0.04 Wilcoxon rank sum). Furthermore, meniscus extrusion graded as absent (n=51), <50% (n=28), and >50% (n=7) correlated with mean cartilage losses 0.02, 0.159, and 0.126 mm, respectively (p=0.0001, Kruskal-Wallis). Multivariable regression analysis with cartilage volume as the primary outcome showed that baseline cartilage thickness (adjusted regression coefficient = -0.051, 95% CI: -0.087, -0.014) and meniscal extrusion (adjusted regression coefficient = 0.115, 95% CI: 0.069-0.160) were the only significant predictors of future cartilage loss (p= 0.008 and p<0.001, respectively). Age, sex, BMI, and dichotomized WORMS scores were not significant at alpha = 0.05. The regression model was significant (p<0.001, R^2=0.44). Changes in KOOS pain scores did not correlate with qMRI cartilage loss (Pearson r=0.018).
CONCLUSION: Baseline cartilage thickness and meniscus extrusion are important and independent predictors for accelerated cartilage loss and development of worsening osteoarthritis. However, the degree of cartilage loss did not correlate with longer-term change in clinical outcome scores, which highlights the complexity that drives symptomatology in osteoarthritis.