Background Chronic musculoskeletal injuries (MSKI) are the joint-most common cause of medical downgrade and discharge. Osteoarthritis (OA) contributes to one-third of US Military medical discharges, likely replicated in the UK military population. Understanding epidemiological trends and predictive tools enables OA prevention (primary, secondary or tertiary), minimising risk for Service Personnel. This study aims to understand rates of progression and incidence, and identify potential predictors, of knee radiographic OA (rOA) and pain (KP) in a military combat-injured cohort.

Methods ADVANCE is a longitudinal cohort study of Afghanistan-deployed UK servicemen (combat-injured, n=579; age, rank, role, service, frequency-matched comparison, n=565). Ninety-two-percent attended Follow-up (n=1052, n=526 per group). Participants completed knee radiographs, venous sampling for OA biomarkers, and Knee Injury and Osteoarthritis Outcome Score, 8- and 11-years post-injury/deployment. Correlation analysis was performed to identify potential predictors (demographic, injury-related, patient-reported, radiological, functional and molecular).

Results Radiographic OA incidence and progression rates increased over 3-years (by 12% and 16%, respectively), but this was not different between trauma-exposed and unexposed individuals (p=0.745 and p=0.443, respectively). However, those with a traumatic-amputation had 2.06x increased rOA incidence risk (p=0.002). Trauma-exposed participants were 1.44x more likely to KP incidence (p=0.024), with those sustaining a knee-specific injury 2.52x more likely to report KP progression (p=0.032). There were inconsistent results from potential predictor variables, with minimal overlap between those with and without a traumatic-amputation. Increased age correlated with increased rOA incidence and progression (both p=0.01), decreased time from injury to rOA progression (p=0.006) and KOOS to KP incidence (p<0.001).

Conclusions This study suggests an initial increased risk of rOA following injury, which plateaus within a few years, postulating a ‘clinical window of maximal intervention’ is required early after rehabilitation. Individuals with lower-limb traumatic-amputation displayed a different trajectory, likely due to altered biomechanics and mechanoinflammation. No potential predictors were consistent across groups, but initial injury-pattern influenced outcomes.