Synovial cyst and ulnar nerve entrapment. A case report.

A 77-year-old man affected by rheumatoid arthritis demonstrated clinical evidence of progressive ulnar nerve compression that proved to be caused by an extra-articular synovial cyst of the elbow. Conservative measures failed to reduce the size of the cyst or to check progress of the ulnar nerve lesion. Surgical treatment by elbow synovectomy and partial cystectomy was effective. The ulnar nerve lesion healed, and the cyst disappeared. Ulnar nerve compression by soft tissue in continuity with a rheumatoid elbow joint is very uncommon. Only one similar case was found in the English-language literature.