Background/Purpose: To determine the prevalence of knee pain (KP),  radiographic knee osteoarthritis (RKOA) and total knee replacements (TKR) in ex-professional footballers compared to general population controls and to determine the associated risk factors.

Methods: 1207 ex-footballers and 4085 controls were recruited in the United Kingdom from professional football associations and the general population in East Midlands respectively. Current KP was defined as pain in or around the knees or most days of the last month. RKOA was examined in a subset of 470 ex-footballers and 491 controls, irrespective of pain status. RKOA was assessed using the Nottingham Line Drawing Atlas (NLDA) scores and the Kellgren Lawrence (KL) grading with a cutoff for OA of ≥3. All known risk factors such as age, body mass index (BMI), knee injury, high risk occupation, 2D4D digit ratio, self-reported constitutional knee alignment and nodal OA were assessed and included in a univariate analysis to identify their significance to knee pain/OA. Values were adjusted for use in a generalised linear model (GLM) with Poisson distribution to determine the relative risk (RR) and 95% confidence interval (CI) of KP and KOA in ex-footballers compared to controls.

Results : The mean age of ex-footballers was 59 years (SD ± 11.7) and that of the controls 62.8 years (SD +10.4) (p<0.01). They were gender matched (all men) with no difference on BMI (p=0.135).  However, ex-footballers had more nodal OA, type 3 finger ratio (2D<4D), pain elsewhere and knee malalignment, knee injuries (65.7% v 24%) but less comorbidities than controls (p<0.001).  Ex-footballers are almost twice as likely to present with KP [RR 1.84, 95%CI 1.71-2.00, P<0.001] and RKOA compared to the controls once adjusting for risk factors [RR 1.69, 95%CI 1.44-1.98 (r/knee) RR 1.69, 95% CI 1.44-1.97 (l/knee), p<0.001]. Ex-footballers report more KP across all age-groups and report onset of KP almost 15-20 years earlier (aged 50-54 years) compared to controls (aged 60-69 years; Figure 1). Ex-footballers reported RKOA (20 years) and TKR (5 years) earlier than controls. They were also almost three times more likely to have a TKR (either unilateral or bilateral) [RR 2.79, 95%CI 2.42-3.23, p<0.001] and a physician diagnosis of OA [RR 2.62, 95% CI 2.32-2.96, p<0.001) and twice as likely to have radiographic chondrocalcinosis [RR 1.78, 95%CI 1.56-2.02, p<0.001].

Figure 1 Prevalence of KP by age in the football and control population

Conclusion: The prevalence of KP, RKOA and TKR are 2-3 times higher and the peak ages of onset are 5-20 earlier in ex-footballers compared to the general population in the UK. The higher prevalence of knee injuries and presumed repetive microtrauma of professional football are likely to be the major attributable factors. Employers and the Industrial Injuries Advisory Council should consider this risk and whether KOA is an industrial compensatable disease.