Objectives:
To examine whether foot/ankle injury and injection contribute to the risk of foot/ankle OA in retired UK male professional footballers.

Methods:
This was a case-control study within retired UK male footballers, where cases reported General Practitioner diagnosed foot/ankle OA or forefoot/ankle surgery after retirement, and controls reported neither. Injury was defined as significant foot/ankle injury with pain for
most days over three months during their career. Injection was defined as injection of corticosteroid or other agents into foot/ankle joints during their career. Adjusted odds ratio (aOR) with 95% confidence intervals (CI) were calculated using logistic regression. Area Under the Curve (AUC) and 95% CI were estimated to examine the contribution of injury and/or injection in the context of other available risk factors.

Results:
Of 424 footballers studied, 63 had foot/ankle OA and 361 had neither. Cases had similar mean age (63.2 versus 63.0, p=0.457) and body mass index (27.7 versus 27.0, p=0.240) as controls, but more foot/ankle injury (73.3% versus 42.5%, p<0.001) and injections (75.0%
versus 48.4%, p<0.001), with aORs of 4.23 (95% CI 1.88-9.48) and 2.62 (95% CI 1.19-5.78), respectively. AUC was 0.69 (95% CI 0.62-0.77) for injury, 0.74 (95% CI 0.66-0.81) for injury and injection, and 0.78 (95% CI 0.70-0.85) for all risk factors. Similar results were observed in footballers with ankle OA only.

Conclusion:
Injury was a major risk factor for foot/ankle OA in retired UK male professional footballers. The role of injection needs cautious interpretation due to potential confounding by indication.