Intraoperative SSEP detection of ulnar nerve compression or ischemia in an obese patient: a unique complication associated with a specialized spinal retraction system.

OBJECTIVE: To report a case of peripheral nerve compression caused by a specialized spinal retraction system, the Thompson-Farley retractor system, that most likely would not have been detected without intraoperative monitoring of the ulnar nerve.
DESIGN: Bilateral median and peroneal nerve somatosensory evoked potentials (SSEPs) were monitored continuously during a C5 corpectomy, as was core body temperature.
RESULTS: Within minutes after cervical soft-tissue retraction, the left ulnar nerve SSEP began to decline in amplitude. Peroneal nerve SSEPs were normal throughout the surgery; core body temperature remained at 36 degrees +/- 0.2 degrees C. After much effort to reposition the patient, the SSEPs returned to baseline and the Thompson-Farley system was replaced by a self-retracting system.
CONCLUSIONS: To our knowledge, this is the first report of peripheral nerve compression caused by the Thompson-Farley retractor system. Even with careful positioning on the operating table, obese patients may be particularly at risk for upper arm compression. Continuous monitoring of SSEPs is suggested to prevent postoperative morbidity.