INTRAOPERATIVE MONITORING OF ULNAR NERVE FUNCTION DURING REPLACEMENT OF THE RHEUMATOID ELBOW VIA THE LATERAL APPROACH

Neurography of the ulnar nerve was performed pre-, intra- and postoper atively in 8 arms of 7 patients with rheumatoid arthritis operated on with total elbow replacement via the lateral approach. Ulnar nerve dec ompression was performed in 4 elbows before implantation. A reduction in the amplitude of compound muscle action potential (CMAP) recorded f rom the abductor djgiti minimi on stimulation of the ulnar nerve in th e axilla, was observed during elbow dislocation at surgery in all pati ents, in 5 cases transiently and in 3 cases until the end of surgery. The ulnar nerve had been decompressed in all patients with lasting amp litude reduction. One of them had a mild sensory ulnar nerve palsy, wh ile the other 2 had normal nerve function at the postoperative clinica l examination. All 3 had a reduction in the amplitude of compound sens ory nerve action potential (SNAP) and 2 of them also in CMAP amplitude at the postoperative neurographic examination. In patients with trans ient reduction during surgery, the CMAP amplitude quickly normalized o n relocation of the elbow and both the SNAP and the CMAP were preserve d at the postoperative neurographic examination. The authors conclude that dislocation of the laterally approached elbow carries a risk of u lnar nerve injury, which is not prevented by decompression of the ulna r nerve, but frequent relocation of the elbow during surgery seems imp ortant. It is suggested that the ulnar nerve should not be decompresse d routinely, and that the dislocated elbow should be frequently reloca ted.