The prevalence of fabella and its association with the osteoarthritic severity of the knee in Korea.

The clinical relevance of the fabella, a sesamoid bone, has recently been investigated. Although many studies have documented the prevalence of the fabella, few large-scale studies have been conducted in an Asian, especially Korean, population. We conducted a retrospective survey of Koreans to determine the prevalence and distribution of the fabella and its association with osteoarthritic severity of the knee. From June 2016 to August 2017, a total of 2243 people who visited a rheumatology clinic for musculoskeletal evaluation was consecutively recruited. A total of 2126 subjects (1634 females and 492 males) was finally registered and analysed. Anteroposterior and lateral radiographs of both knees were analysed for presence, number and distribution of fabellae and Kellgren-Lawrence grade. The prevalence of the fabella was 57.2% (57.5% for females, 56.1% for males). Among subjects with a fabella, 21.2% had a unilateral distribution, and 78.8% had a bilateral distribution. The number of fabella was correlated with increasing age (r = 0.169, p < 0.001). In the group of subjects with a fabella, the Kellgren-Lawrence grade was significantly higher than in the group without a fabella (2.64 ± 1.38 vs. 1.89 ± 1.54, p < 0.001). The prevalence of fabella in Koreans was relatively high compared with the findings of previous studies, irrespective of the country studied or methodology used. The number of fabellae tended to increase with age. The osteoarthritic severity of the knee appeared worse in the group with a fabella. Key Points • The radiographical prevalence rate of fabella in Korea was about 58%, higher than the previous results. • The prevalence of fabella increased as the age of the subject increased regardless of gender. • The association between fabella and osteoarthritis is strongly suspected because the osteoarthritic changes in the knee of the subjects with fabella are significantly higher than in the subjects without fabella.