Objectives: To evaluate the reliability and validity of the Norfolk Arthritis Register Damaged Joint Count (NOAR-DJC) in patients with early inflammatory polyarthritis (IP).
Methods: The NOAR-DJC examines deformity in 51 joints. Deformity is defined as inability to adopt the anatomical position, reduction in range of movement by at least one-third, and/or surgical alteration of the joint. Reliability was investigated by assessing intra- and inter-observer agreement in 40 and 32 patients, respectively. Validity was assessed by correlating the NOAR-DJC with the eroded joint count (criterion validity), the Health Assessment Questionnaire (HAQ) (convergent construct validity) and tender and swollen joint counts (divergent construct validity) and by discriminating between those who did and did not satisfy criteria for rheumatoid arthritis (discriminant validity).
Results: The intraclass correlation coefficient for the intra- and inter-rater studies were 0.88 [95% confidence interval (CI) 0.79, 0.94, P<0.00001] and 0.74 (95% CI 0.53, 0.86, P<0.00001), respectively. Correlations with eroded joint counts and HAQ scores after 5 yr follow-up were r(s) = 0.42 (95% CI 0.35, 0.49, P<0.01) and r(s) = 0.45 (95% CI 0.4, 0.5, P<0.01), respectively. Correlations with tender and swollen joint counts were weak (r(s) = 0.28 and r(s) = 0.33).
Conclusion: The NOAR-DJC is a quick, reliable and valid tool for assessing articular damage in patients with early IP.