Background/Purpose: Football is the world’s most popular team sport. However, whether professional footballers have a higher prevalence of knee injury and subsequently, knee pain (KP), radiographic knee osteoarthritis (RKOA) and total knee replacement (TKR) than the general population remains largely unknown. We therefore undertook a population-based study comparing ex-professional footballers and the general population to (1) determine the prevalence of KP, RKOA and TKR; and (2) investigate the specific risk factors associated with these three conditions. This is the second part of the project, aiming to determine the specific risk factors that are associated with KP, RKOA and TKR within footballers.

Methods: A case control study was undertaken in footballers, where cases were defined as footballers with KP, RKOA or TKR and controls were those without these outcomes. A questionnaire survey was undertaken in 4775 retired professional footballers in the UK, via Football Clubs and organisations (including the Professional Footballers Association). 1207 footballers (25.3%) responded to the survey and 472 additionally agreed to undergo standardised bilateral knee radiographs. Potential risk factors were collected through the questionnaire. KP was defined as pain in or around the knees for most days of the last month. RKOA was assessed via weight-bearing semi-flexed posterior-anterior and 30° flexion skyline views and graded using the Kellgren-Lawrence (KL) system (RKOA defined as KL≥3) and the Nottingham Line Drawing Atlas (NLDA). TKR was a self-reported measure, confirmed in some by x-ray. Significant risk factors for each outcome were determined using multivariate logistic regression and reported as odds ratio (OR) with 95% confidence interval (CI).

Results: The prevalence of KP in footballers was 52.2%, which is twice as common as the general population (25.2% reported in Study Part 1 abstract). Knee injury and its subsequent investigations/interventions (exploratory and/or corrective surgery) and management (intra-articular knee injections) were associated with KP. While a number of other significant risk factors were identified for KP, very few were identified for RKOA and none for TKR (Table 1).

Table 1 ^#surgical intervention, which includes exploratory, corrective and/or lesser surgery. OR adjusted for age and BMI; *p<0.05, †p<0.01, ‡p<0.001

Conclusion: Knee injuries, together with subsequent investigations (specifically exploratory and interventional arthroscopy) and management (specifically intra-articular knee injections), were strongly associated with risk of later KP and RKOA. Football organisations need to be mindful of these data and apply strategies to minimise the risk of knee injury (and subsequent investigation and management) in professional football players.