Risk Factors for Knee Osteoarthritis in Retired Professional Footballers: A Cross-Sectional Study

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Objective: To determine risk factors for 3 knee osteoarthritis (KOA) outcomes, knee pain (KP), radiographic KOA (RKOA), and total knee replacement (TKR) in professional footballers. Design: This was a cross-sectional study involving a postal questionnaire, followed by radiographic assessment in a subcohort of responders. Settings and Participants: Four thousand seven hundred seventy-five questionnaires were sent to retired professional footballers, who had played in the English football league, and 1207 responded. Of these, 470 underwent knee radiographs. Assessment of Risk Factors: Potential factors include age, body mass index (BMI), knee alignment, a history of football-related knee injury, and training hours (during career) were collected through the questionnaire. Main Outcome Measures: Knee osteoarthritis outcomes were current KP (pain for most days of the previous month), TKR (self-reported), and RKOA (observed through radiographs). Results: Football-related injury was the strongest risk factor for KP [adjusted odds ratio (aOR), 4.22; 95% confidence interval (CI), 3.26-5.48], RKOA [aOR, 2.88; 95% CI, 1.81-4.59], and TKR [aOR, 4.83; 95% CI, 2.87-8.13]. Footballers had a 7% increased risk of RKOA for every 1000 hours trained. Although age and gout were associated with all 3 KOA outcomes, BMI, nodal osteoarthritis (OA), a family history of OA, knee malalignment, and 2D:4D ratio were associated with one or another of these 3 KOA outcomes. Conclusion: This study is the first to examine KOA risk factors in retired professional footballers. The study has identified several risk factors, both specific (eg, knee injury and training dose) and nonspecific (eg, age and gout) to footballers. This may be used to develop prevention strategies to reduce the risk of KOA in professional footballers after retirement.