Assessment at CT of the rheumatoid shoulder with surgical correlation.

Eleven shoulders in 10 patients with rheumatoid arthritis were examined by conventional radiography and CT prior to cup hemiarthroplasty of the humeral head and the results were compared with the surgical findings. There was good agreement between preoperative CT and surgical findings. Humeral head cavities and erosions, with cortical boundaries, could be seen more accurately at CT than at conventional radiography. The HU of their contents corresponded to those of soft tissue, being granulomatous in nature at surgery. In 8 humeral heads CT disclosed large areas of fatty degeneration of bone marrow with HU between -10 HU and -76 HU that were not visible on the conventional radiographs. These "fatty cysts" had no cortical boundaries, unlike inflammatory granulomas, but both lesions may influence the surgical approach to hemiarthroplasty.