Objective
The ArmeD SerVices TrAuma RehabilitatioN OutComE (ADVANCE) study is investigating long-term combat-injury outcomes; this sub-study aims to understand the association of osteoarthritis (OA) biomarkers with knee radiographic OA (rOA), pain and function in this high-risk population for post-traumatic OA.

Design
ADVANCE compares combat-injured participants with age, rank, deployment and job-role frequency-matched uninjured participants. Post-injury immunoassay-measured serum biomarkers, knee radiographs, knee injury and osteoarthritis outcome scale (KOOS), and six-minute walk-tests (6MWT) are reported. The primary analysis, adjusted for age, body mass, socioeconomic status, and ethnicity, was to determine any differences in biomarkers between those with/without combat-injury, rOA and pain. Secondary analyses were performed to compare post-traumatic/idiopathic OA, painful/painfree rOA and injury patterns.

Results
1145 male participants were recruited, aged 34.1±5.4, 8.9±2.2 years post-injury (n=579 trauma-exposed, of which, traumatic-amputation n=161) or deployment (n=566 matched). Cartilage oligomeric matrix protein (COMP) was significantly higher in the combat-injured group compared to uninjured (p=0.01). Notably, COMP was significantly lower in the traumatic-amputation group compared to non-amputees (p<0.001), decreasing relative to number of amputations (p<0.001). Leptin was higher (p=0.005) and adiponectin lower (p=0.017) in those with v without knee pain, associated with an increased risk of 22% and 17% for pain, and 46% and 34% for painful rOA, respectively. There were no significant differences between trauma-exposed and unexposed participants with rOA.

Conclusions
The most notable findings of this large, unique study are the similarities between those with rOA regardless of trauma-exposure, the injury-pattern and traumatic-amputation-associated differences in COMP, and the relationship between adipokines and pain.