Repeatability of quantification of extrusion of the medial meniscus in knee osteoarthritis using three-dimensional models.

Objective: Meniscal damage is one of risk factors for the development of knee osteoarthritis (KOA). Medial meniscal extrusion (MME) is associated with the progression of cartilage loss in the medial compartment. The objective of this study was to determine the intra-rater repeatability of our method of three-dimensionally analyzing MME in patients with KOA. Design: Eight knees with medial KOA were examined in participants aged between fifty and eighty years old. We created three-dimensional models of the tibia and medial meniscus using a 0.4 Tesla MRI scanner and embedded a local coordinate system into the tibia. Repeatability of measurements of the MME volume and width were tested using intraclass correlation coefficient (ICC). Results: The ICC for measuring the MME volume was 0.998 [95% confidence interval, 0.992, 1.000]. Measurement error for the MME volume was 0.5-7.0%. The ICC for measuring the MME width was 0.983 [0.924, 0.996]. Measurement error for the MME width was 0.0-11.4%. There was no correlation between the MME volume and width (r = 0.565, p = 0.145). Conclusions: This study concluded that three-dimensional volume and width measurements of the MME by a single rater using MRI images had high repeatability even in the limited image quality. The result of non-significant correlation between the MME width and volume suggests that MME width measured using a low-magnet MRI scanner not considered reliable. Further studies are needed to determine the association between the MME volume and disease progression of KOA.