Association of femoroacetabular impingement with the 5 year incidence of hip osteoarthritis: A Japanese community-based cohort study

Hip osteoarthritis (OA) is a major cause of disability in older adults. While femoroacetabular impingement (FAI) is considered a structural risk factor for OA development, longitudinal evidence from Asian general populations remains limited. This community-based Japanese cohort study evaluated the association between radiographic and physical examination findings related to FAI with the incidence of hip OA. This 5 year community-based cohort study included 483 Iwaki Health Promotion Project participants without radiographic hip OA [Kellgren–Lawrence (KL) 0–1] at baseline. Standing anteroposterior (AP) hip radiographs and physical examinations were obtained in 2014 and 2019. Incident hip OA was defined as KL ≥ 2 at follow-up. Radiographic assessment included evaluation of pistol grip deformity (PGD) and AP radiographic parameters, and Cam-type FAI was defined as the presence of PGD with a center edge angle ≥25°. Physical examination findings, including the anterior impingement sign (AIS) and Patrick's test, were also assessed. Logistic regression analyses adjusted for age, sex, and body mass index were performed to identify factors associated with incident hip OA. Among 483 eligible participants, 64 (13.3%) developed incident hip OA over the 5 year follow-up. Cam-type FAI findings were associated with incident hip OA [relative ratio (RR) 4.03, 95% confidence interval (CI) 1.52–10.65]. AIS was also associated with incident hip OA (RR 2.34, 95% CI 1.01–5.42). Radiographic findings suggestive of Cam-type FAI were associated with the incidence of hip OA. While AIS also showed an association, this non-specific finding should be interpreted cautiously. Simple AP radiographic features may help identify individuals at increased risk of developing hip OA. • Simple anteroposterior (AP) radiological features may predict high osteoarthritis (OA) risk. • Cam-type femoroacetabular impingement on AP radiographs predicted incident hip OA in Japan. • A positive anterior impingement sign may increase the risk of developing hip OA.