Extrusion of the medial meniscus in knee osteoarthritis assessed with a rotating clino-orthostatic permanent-magnet MRI scanner.

PURPOSE: The objectives of this study were to assess the influence of weight-bearing on tibiofemoral osteoarthritis, including medial meniscal extrusion, by using a low-field (0.25 T) rotating clino-orthostatic permanent-magnet magnetic resonance (MR) scanner, and to analyse correlations of medial meniscal extrusion with the patient's Kellgren-Lawrence score, body mass index, and all the osteoarthritis features of the WORMS scoring system.
MATERIALS AND METHODS: Twenty-six patients (69.2% women and 30.8% men; mean age 67 ± 9.7 years) with medial tibiofemoral knee osteoarthritis were prospectively enrolled and MR sequences were acquired in both clino- and orthostatic position. MR images were assessed by two independent radiologists, according to the WORMS scale. Medial meniscal extrusion was measured and its clino-orthostatic difference (∆MME) was calculated.
RESULTS: Intra- and inter-observer agreement of the WORMS Global Score readings was high by Cohen's K test (>0.81). No significant clino-orthostatic changes in the scoring parameters of the medial tibiofemoral joint were shown by Wilcoxon's test. Medial meniscal extrusion measured on orthostatic images was significantly higher than that measured in clinostatic position (p < 0.0001). At univariate analysis, the Kellgren-Lawrence score, WORMS Global Score, cartilage loss, meniscal damage, and osteophytes were significantly correlated to ∆MME (p < 0.005). Using a multiple regression model, tibiofemoral cartilage loss was found to correlate independently with ∆MME (p = 0.0499).
CONCLUSIONS: Medial meniscal extrusion, evaluated with an open-configuration, rotating MR scanner, increased from the clinostatic to the orthostatic position. ∆MME, a new meniscal parameter, correlated with several important features of medial tibiofemoral osteoarthritis.