OBJECTIVE: To compare in images obtained by High-Resolution peripheral Quantitative Computed Tomography(HR-pQCT) and conventional radiography(CR) of the second and third metacarpophalangeal(MCP) joints the minimal erosive cortical break needed to differentate between pathological and physiological cortical breaks.

METHODS: In this single-centre cross-sectional study, patients with established RA(disease duration ≥ 5 years) had their second and third MCP joints of the dominant hand investigated by HR-pQCT and CR. Empirical estimation was used to find the optimal cutoff value for the number of erosions and total erosive volume, which were detectable between patients with and without erosions in the second and third MCP joints according to CR.

RESULTS: The total erosive volume in the second and third MCP joints by HR-pQCT for CR detected erosive disease was estimated to be 56.4(95% CI: 3.5 - 109.3) mm 3. The sensitivity and specificity at this cutpoint were 78% and 83%, with an area under the receiver operating characteristic curve(AUC) of 0.81. The optimal cutoff value for the number of erosions by HR-pQCT was 8.5(95% CI:5.9 - 11.1) for CR detected erosive disease in the second and third MCP joints by CR. The sensitivity and specificity at this cutpoint were 74% and 88%, respectively, with an AUC of 0.81.

CONCLUSION: Erosions by HR-pQCT were larger in patients with erosive damage in the second and third MCP joints by CR. We found that CR had poor sensitivity for detecting erosive disease when the erosive volume was less than 56.4 mm 3 or the number of erosions less than 8.5.