Ability of oblique foot radiographs to detect erosions in early arthritis: results in the ESPOIR cohort.

Objective: To assess the usefulness of using oblique foot radiographs in addition to posteroanterior radiographs of the hands and feet for detecting erosions in patients with recent-onset arthritis.

Methods: We included 813 patients from the prospective French ESPOIR cohort with arthritis of <6 months' duration and >or=2 swollen joints. Baseline standardized posteroanterior radiographs of the hands and feet and oblique radiographs of the feet were assessed by 2 blinded readers for erosions typical for rheumatoid arthritis (ETRA) and the Sharp score as modified by van der Heijde.

Results: A total of 715 complete sets were available. Mean +/- SD total Sharp scores were 3.6 +/- 6.6, 2.5 +/- 6.3, and 1.8 +/- 5 for the hand and wrist, foot, and oblique foot, respectively. ETRA were visible in 160 (22.4%) of 715 patients (95% confidence interval [95% CI] 19.4-25.6). They were seen on hand radiographs in 86 (53.7%) of 160 patients (95% CI 45.7-61.6), on posteroanterior foot radiographs in 91 (56.9%) of 160 patients (95% CI 48.8-64.6), and on oblique foot radiographs in 84 (52.5%) of 160 patients (95% CI 44.5-60.4). ETRA were visible at the feet, but not at the hands, in 74 (46%) of 160 patients (95% CI 38.4-54.3), among whom 22 (30%) had erosions only on the posteroanterior view, 16 (21%) only on the oblique view, and 36 (48.6%) on both.

Conclusion: ETRA were found in 22.4% of patients. Adding an oblique foot radiograph identified 16 (10%) of 160 additional patients (95% CI 6-16), compared with 27.5% and 13.8% identified by adding posteroanterior radiographs of the hands and feet, respectively.