Abstract

Purpose: Meniscus function is important in knee osteoarthritis (knee OA), and aging-related dysfunction of meniscus is becoming a risk factor for the development and progression of knee OA. Recently, meniscal malposition, especially medial meniscus extrusion (MME), in addition to conventional meniscal damage is also attracting attention, and it has been shown that MME plays an important role for the incidence and progression of knee OA. However, the mechanism of the developmental process of MME is still remained unclear. In our recent study using T2 mapping MRI, MME was found in all cases with early stage knee OA patients who did not have meniscal lesion or tear. We also demonstrated that osteophyte consists of cartilage- and bone-parts, as osteophyte is formed by the process similar to the endochondral ossification. When cartilage-part of osteophyte, in addition to bone-parts, was evaluated, MME was coincided with the medial tibial osteophyte width in patients with early- to primary-stage knee OA (Arthritis Res Ther, 19:201, 2017). However, there is no report of the prevalence of MME in the general elderly cohort data. The purpose of this study was to examine the prevalence of MME among the elderly using a population-based cohort data. Methods: A total of 1,630 subjects aged between from 65 to 84 years of age participated in the Bunkyo Health Study during from November 2015 to September 2018. 1,191 subjects underwent both the plain radiograph in the standing position and MRI on knee joint (Hitachi, 0.3T). As 46 among 1,191 who showed lateral type of knee OA (femoro-tibial angle <173) were excluded, the remaining 1145 subjects (55.7% females, 72.9 years of age on average) were analyzed. A radiographic severity of knee OA was classified into four grades using the Kellgren-Lawrence (K/L) classification. FTA and medial joint space width (JSW) were measured with X-ray. The MME was evaluated according to whole organ magnetic resonance imaging score (WORMS). In addition, the position of the medial meniscus was measured for anomalies (1 mm or more was regarded as a position error), and 3 mm or more was defined as MME. A p-value less than 5% was considered to be statistically significant. All analyses were undertaken using the statistical package SPSS. Results: The severity of radiographic medial knee OA of the subjects in the present study was 16 (1.4%) for K/L 1, 986 (86.1%) for K/L 2, 106 (9.3%) for K/L 3, and 37 (3.2%) for K/L 4. Abnormal position of medial meniscus was detected in almost all cases (1,139 persons, 99.5%, 4.4±2.1mm on average). The MME was detected 842 persons (73.5%). Prevalence by generation of the MME was increased with each generation (p<0.001): 70.7% for 65-70 years of age, 74.1% for 70-75 years of age, 74.7% for 75-80 years of age, 79.9% >80 years of age. Abnormal position of the medial meniscus was associated with FTA (r = 0.18 p <0.001), JSW (r = -0.20 p <0.001), and age (r = 0.13 p <0.001). Conclusions: In the present population-based study, most of the subjects among the middle aged and elderly populations who did not require the medical treatment for their knee joint showed the K/L grade 2 of radiographic knee OA change. In elderly people over the age of 65 in Japan, most of the medial meniscus had an abnormal position, and more than 70% of medial meniscus categorizes to MME. In addition, the probability of MME becomes higher with age.

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