Knee meniscal extrusion in a largely non-osteoarthritic cohort: association with greater loss of cartilage volume

We conducted a longitudinal study (duration 2 years), including 294 individuals (mean age 45 years, 58% female), in order to examine associations between meniscal extrusion, knee structure, radiographic changes and risk factors for osteoarthritis (OA) in a largely non-osteoarthritic cohort. Meniscal extrusion, tibiofemoral cartilage defect score and cartilage volume, and tibial plateau bone area were determined using T1-weighted fat-saturated magnetic resonance imaging. At baseline the presence of medial meniscal extrusion was significantly associated with body mass index (odds ratio [OR] per kg/m² = 1.13, 95% confidence interval [CI] = 1.02–1.25), past knee injury (positive versus negative history: OR = 3.73, 95% CI = 1.16–11.97), medial tibial bone area (OR per cm² = 1.37, 95% CI = 1.02–1.85), and osteophytes (OR per grade = 4.89, 95% CI = 1.59–15.02). Two-year longitudinal data revealed that medial meniscal extrusion at baseline was associated with a greater rate of loss of medial tibiofemoral cartilage volume (extrusion versus no extrusion: -1.4%/year; P < 0.05) and greater risk for increased medial femoral cartilage defects (OR = 2.59, 95% CI = 1.14–5.86) and lateral tibial cartilage defects (OR = 2.64, 95% CI = 1.03–6.76). However, the latter two associations became nonsignificant after adjustment for tibial bone area and osteophytes. This study suggests that increasing body mass index and bone size, past knee injury, and osteophytes may be causally related to meniscal extrusion. Most importantly, meniscal extrusion at baseline is associated with greater loss of knee cartilage over 2 years, and this seems to be mediated mostly by subchondral bone changes, suggesting extrusion represents one pathway between bone expansion and cartilage loss.