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Use of digital x ray radiogrammetry in the assessment of joint damage in rheumatoid arthritis

¹ Department of Rheumatology, NHS Grampian, Ward 3, Aberdeen Royal Infirmary, Aberdeen, AB25 2ZN, UK
² Department of Medicine and Therapeutics, University of Aberdeen, Aberdeen, UK

Correspondence to:
Correspondence to:
Professor D M Reid
Department of Medicine and Therapeutics, University of Aberdeen, Medical School, Foresterhill, Aberdeen, AB25 2ZD, UK; d.m.reid{at}abdn.ac.uk

Objective: To compare digital x ray radiogrammetry (DXR) with manual radiography for assessing bone loss in RA and examine the relationship of the scores obtained with other disease indices.

Methods: 225 consecutive consenting subjects attending the RA clinic were enrolled. An x ray examination was carried out; demographic details recorded; a self assessment questionnaire completed; blood taken for ESR measurement; and an assessment made by a trained nurse. All x ray films were scored manually using the modified Sharp technique by a single observer; 20 films were rescored by three readers. Films were assessed with the Pronosco X-Posure system, version 2.0. Analysis included ² tests, independent t tests, multiple linear regression, and partial correlations, as appropriate. The smallest detectable difference (SDD), coefficient of variation (CV), and coefficient of repeatability (CR) were determined from Bland and Altman plots.

Results: The DXR precision varied: SDD = 0.002–0.9; CV = 0.09–5.9%; CR = 0.002–0.792, but was better than that of the intra- and interobserver Sharp scores: SDD = 73.9; CV = 27.8%; CR = 33.0–47.6. The DXR measurements, bone mineral density (R² = 0.210), metacarpal index (R² = 0.222), and cortical thickness (R² = 0.215), significantly predicted Sharp scores. In women, DXR measurements significantly correlated with modified HAQ scores but with no other disease indices. Sharp scores significantly correlated with assessor’s global assessment, swollen and tender joint counts, pain, HAQ, and DAS28.

Conclusion: DXR measurements are more precise than Sharp scores; both are related to long term disease activity in RA. DXR is simple to use, does not require intensive training, and may identify subjects not responding to standard treatment.

Abbreviations: BMD, bone mineral density; CR, coefficient of repeatability; CV, coefficient of variation; AGA, assessor’s global assessment; BW, bone width; CT, cortical thickness; DAS28, 28 joint count disease activity score; DXA, dual energy x ray absorptiometry; DXR, digital x ray radiogrammetry; EMS, early morning stiffness; ESR, erythrocyte sedimentation rate; HAQ, Health Assessment Questionnaire; MCI, metacarpal index; PGA, patient global assessment; POR, porosity; RA, rheumatoid arthritis; SDD, smallest detectable difference; VAS, visual analogue scale

Keywords: rheumatoid arthritis; joint erosions; hand bone density; radiogrammetry