Medial plica is associated with progression of medial meniscus extrusion in middle-aged persons with Kellgren–Lawrence grade 0: data from the osteoarthritis initiative

Background Medial plica is a structure with limited understanding of its pathology, but it may be related to the development of medial knee osteoarthritis (OA). We examined the association between medial plica and medial meniscus extrusion (MME), progression of MME, and the risk of early-stage knee OA development in middle-aged persons. Methods A total of 340 subjects with tibiofemoral Kellgren–Lawrence (K/L) grade 0 from the Osteoarthritis Initiative were included. We evaluated magnetic resonance imaging (MRI) data (right knee) at baseline and six years later. At baseline, the severity of medial plica (grade 0–3), extent of MME (grade 0–3) as well as measured MME in mm was determined. After six years, changes in MME (ΔMME), cartilage loss, and the formation of osteophytes were evaluated. Results Medial plica (grade ≥ 1) was observed in 280 subjects (82.4%) at baseline, of whom 13 subjects had grade 3 plica. The MME was 1.7 ± 0.8 mm at baseline and 2.1 ± 0.9 mm after 6 years. Progression of MME was observed in 83 subjects (24.5%) after 6 years. The cartilage loss after 6 years in subjects with medial plica grade ≥ 1 at baseline was greater than that in subjects without medial plica (Δcartilage score 2.9 ± 2.8 vs. 2.2 ± 3.0, p = 0.01), although the difference was borderline when analyzed across all plica grades ( p = 0.05). The ΔMME was greater for higher grades of medial plica at baseline ( p = 0.01). Subjects with medial plica grade ≥ 1 had a higher risk of progression of MME grade (odds ratio [OR] 2.1, 95% CI 1.0–4.5, p = 0.04), but this was not significant for grade ≥ 2 in sensitivity analysis (OR 1.2, p = 0.50). Progression of K/L grade was observed only for medial plica grade ≥ 2 (OR 2.1, 95% CI 1.1–4.2, p = 0.03), but not for grade ≥ 1. Conclusion In middle-aged persons with K/L grade 0, the presence of medial plica—particularly higher-grade lesions—was associated with progression of MME and cartilage loss, and grade ≥ 2 lesions were additionally associated with radiographic progression of knee OA.