Ulnar compression neuropathy due to an occult post-traumatic synovial cyst.

A patient presented with an ulnar nerve palsy which developed some time after minimal trauma to the arm. It was thought that the paralysis was possibly caused by leprosy, but because of doubt about the diagnosis, biopsy of the nerve was advised. At operation, it was found that there was nerve compression by a slowly developing occult synovial cyst of the elbow joint, which had tracked down the tight confines of the cubital tunnel. If there is doubt as to whether an isolated ulnar palsy is caused by leprosy, it may be reasonable to explore the nerve at the level of the cubital tunnel. If compression is found, it can be relieved. If the nerve itself appears abnormal, the epineurium can be biopsied.