A novel classifier of radiographic knee osteoarthritis for use on knee DXA images is predictive of joint replacement in UK Biobank

DXA scans may offer a novel means of evaluating radiographic knee OA (rKOA) in large population studies and through opportunistic screening. We aimed to develop and apply a semi-automated method for assessing rKOA using ≈20 000 knee DXA images from UK Biobank (UKB) and assess its face validity by checking for expected relationships with clinical outcomes.Right knee DXA scans were manually annotated for osteophytes to derive corresponding grades. Joint space narrowing (JSN) grades in the medial joint compartment were determined from automatically measured minimum joint space width. Overall rKOA grade (0–4) was determined by combining osteophyte and JSN grades. Logistic regression was employed to investigate the associations of osteophyte, JSN and rKOA grades with knee pain and hospital-diagnosed KOA. Cox proportional hazards modelling was used to examine the associations of these variables with risk of subsequent total knee replacement (TKR).Of the 19 595 participants included (mean age 63.7 years), 19.5% had rKOA grade ≥1 (26.1% female, 12.5% male). Grade ≥1 osteophytes and grade ≥1 JSN were associated with knee pain, hospital-diagnosed KOA and TKR. Higher rKOA grades were linked to stronger associations with these clinical outcomes, with the most pronounced effects observed for TKR. Hazard ratios for the association of rKOA grades with TKR were 3.28, 8.75 and 28.63 for grades 1, 2 and 3–4, respectively.Our DXA-derived measure of rKOA demonstrated a progressive relationship with clinical outcomes. These findings support the use of DXA for classifying rKOA in large epidemiological studies and in future population-based screening.What does this mean for patients?Knee osteoarthritis (KOA) is a common condition causing pain and disability, often requiring knee replacement surgery. Diagnosing KOA typically involves X-rays to detect changes such as bone growths (osteophytes) and narrowing between bones (joint space narrowing). However, using X-rays in large studies is time-consuming and subjective. Dual-energy X-ray absorptiometry (DXA), a low-radiation imaging method primarily used to measure bone density, offers a promising alternative for KOA assessment. In this study, we analysed nearly 20 000 knee DXA scans from UK Biobank, using computer-aided techniques to measure osteophytes and joint space narrowing. We found that higher grades of DXA-derived radiographic KOA were strongly linked to knee pain, hospital-diagnosed KOA and total knee replacement. These findings suggest that DXA scans can effectively identify KOA and its progression, making them valuable for large studies. As DXA is already widely used for bone health checks, this method could enable early detection and better management of KOA, improving outcomes for patients.