Objectives To examine the construct validity of MRI in the detection of structural hand osteoarthritis features with conventional radiography (CR) as reference and explore the association between radiographic severity and MRI-defined pathology.

Methods 106 hand osteoarthritis patients (97 women, mean age 68.9 years (SD 5.6)) had 1.0T contrast-enhanced MRI and CR of the dominant hand. The 2nd–5th interphalangeal joints were scored according to the preliminary Oslo hand osteoarthritis MRI score and Kellgren–Lawrence (KL) scale and Osteoarthritis Research Society International atlas for radiographs. The authors compared the number of joints with structural features by MRI and CR (Wilcoxon signed-rank test) and examined concordance at the individual joint level. The OR of MRI features in joints with doubtful (KL grade 1), mild (2) and moderate/severe (≥3) radiographic osteoarthritis was estimated by generalised estimating equations (KL grade 0 as reference).

Results MRI detected approximately twice as many joints with erosions and osteophytes compared with CR (p<0.001), but identification of joint space narrowing, cysts and malalignment was similar. The sensitivity of MRI was very high for osteophytes (1.00) and erosions (0.95), while specificity was lower (0.22 and 0.63). The prevalence of most MRI features increased with radiographic severity, but synovitis was more frequent in joints with mild osteoarthritis (OR2.1, 95% CI 1.4 to 3.2) than in moderate/severe osteoarthritis (OR1.4, 95% CI 1.0 to 2.2).

Conclusion MRI detected more osteophytes and erosions than CR, suggesting that erosive osteoarthritis may be more common than indicated by CR. Synovitis was most common in mild osteoarthritis. Whether this is due to burn-out of inflammation in late disease must be investigated further.