Objective To validate ultrasound (US) for measuring metacarpal cartilage thickness (MCT), by comparing it with anatomical measurement using cadaver specimens. To correlate US MCT with radiographic joint space narrowing (JSN) or width (JSW) in patients with rheumatoid arthritis (RA).

Methods Bilateral metacarpophalangeal (MCP) joints of 35 consecutive outpatients, with recent hand X-rays, were included in the analysis. Metacarpal and phalangeal cartilage of MCP 2–5 was assessed bilaterally by US. JSW and JSN were evaluated on X-rays by the van der Heijde modified Sharp method (vdHS). In addition, cadaver specimens of MCP 2–5 joints (n=19) were evaluated by anatomical measurement and US.

Results The agreement (intraclass correlation coefficient) between sonographic and anatomical MCT on cadaver specimens of MCP joints was 0.61. MCT of individual MCP joints correlated with individual MCP JSN (r=−0.32, p<0.001) and individual MCP JSW (r=0.72, p<0.001). No correlation was found between phalangeal cartilage thickness and JSN in individual MCP joints. The US MCT summary score for MCP joints 2–5 correlated with summary scores for JSW (r=0.78, p<0.001), JSN (r=−0.5, p<0.001), erosion score of the vdHS (r=−0.39, p<0.001) and total vdHS (r=−0.47, p<0.001).

Conclusions Sonographic cartilage assessment in MCPs is closely related to anatomical cartilage thickness. Both JSW and JSN by radiography represent cartilage thickness in the MCP joints of patients with RA quite well. Thus, US is a valid tool for measuring MCT if radiographs are not available or in case of joint malalignment.