To test whether bony lesions appearing on ultrasound (US) imaging are cortical breaks detectable by micro-computed tomography (micro-CT).
Twenty-six subjects (14 with rheumatoid arthritis, 6 with psoriatic arthritis, and 6 healthy controls) were assessed for bone erosions at the radial, palmar, and dorsal regions of the second metacarpophalangeal (MCP) joint and the palmar and dorsal regions of the third and fourth MCP joints. All patients underwent US and, for validation of the results, micro-CT scanning. The prevalence and severity of bone erosions as determined by US and by micro-CT were recorded and compared.
Overall there was a good correlation between the severity of erosions as assessed by US and by micro-CT (r = 0.463, P < 0.0001). False-negative results (US negative/micro-CT positive) were obtained in only 9.9% of the joint regions and were mostly due to small erosive lesions at the dorsal sides of the MCP joints. False-positive results (US positive/micro-CT negative) were more frequent (28.6%) and were primarily based on vascular bone channels at the palmar sides of the MCP joints as well pseudo-erosions created by osteophytes.
These data show that the majority of bone lesions appearing on US are indeed bone erosions with a cortical break. The sensitivity of US for detecting bone erosions was high and there was a good correlation between the severity of bone erosions as assessed by US and as assessed by micro-CT. Specificity of US for bone erosions was substantially lower, suggesting that smaller lesions seen on US do not always represent breaks in the cortical bone surface.