Objective: To compare the correlation and specificity of the combined cortical thickness of the second metacarpal (CCT-MC) with Sharp's method (SM) for scoring joint erosions and joint space narrowing in rheumatoid arthritis (RA) and to compare the degree of interobserver agreement between the 2 methods.
Methods: Hand microradiographs of 22 women with RA, functional classes III and IV, were scored independently by 3 rheumatologists using the CCT-MC and the CCT of the middle phalanx and SM.
Results: (1) There was a highly significant correlation between the total SM score and the CCT-MC for the 3 observers (r = 0.61, p = 0.0026), but not between the CCT of the middle phalanx and SM (r = 0.15, p = 0.53). There was a lower degree of agreement between the observers for SM erosion scores compared to the CCT-MC (intraclass correlation 0.88 for the CCT-MC and 0.63 for the SM); (2) Both joint space narrowing and erosion scores correlated highly with the CCT-MC (r = -0.60, p = 0.004; and r = -0.51, p = 0.014, respectively); (3) CCT-MC measurements are more closely related to the inner (d) as opposed to the outer (D) diameter of the 2nd metacarpal; (4) The mean time to obtain the CCT-MC score was 3.43 min (SD = 1.38) versus 9.83 min (SD = 3.20) for SM (p = 0.0001); (5) the derivative, (D2-d2)/D2, was significantly correlated with SM (r = -0.72, p = 0.0002) and its erosion and joint space narrowing components (r = -0.63, p = 0.0019; and r = -0.71, p = 0.0002, respectively).
Conclusion: The CCT-MC is a rapid, practical method with higher agreement among observers compared to SM and correlates highly with SM scores for joint damage in RA. CCT-MC appears to have a higher degree of specificity than other sites for CCT measurement. The CCT-MC is more closely related to the inner diameter than the outer diameter, which supports the notion that the principal site of accelerated bone loss due to RA in the hand occurs at the endosteal surface. The CCT-MC should be further assessed with respect to monitoring radiological progression in RA.