The Effects of Noninvasive Traction on SSEPs During Ankle Arthroscopy

Background: The purpose of this study was to evaluate the effects of noninvasive ankle distraction on intraoperative somatosensory evoked potentials (SSEPs) and peripheral nerve sensibility of the foot during ankle arthroscopy.

Methods: Twenty patients undergoing ankle arthroscopy were prospectively evaluated using noninvasive ankle traction. All had preoperative clinical examination with baseline neurologic evaluation and static 2-point discrimination (2PD) test. Intraoperative SSEPs were monitored continuously throughout surgery. Thirty pounds of traction was applied using noninvasive traction. A 50% decrease in amplitude or a 10% increase in latency was considered significant. At 2 weeks postoperatively, the 2PD test was repeated. Pre- and postoperative 2PD was compared and subsequently correlated with intraoperative SSEPs.

Results: Three patients sustained significant SSEP signal alterations during surgery. The changes were transient and directly related to application of traction but returned to baseline without traction release. Abnormal postoperative 2PD testing was found in the operative extremity in 12 patients but resolved by the second postoperative visit. Only 2 of 12 had intraoperative SSEP changes. Eleven patients had abnormal postoperative 2PD testing in the nonoperative limb. Nine had changes in both limbs. Routine history and clinical examination did not suggest any neurologic injury. There was no statistically significant correlation between intraoperative SSEP alterations and subsequent development of abnormal postoperative 2PD testing.

Conclusion: Transient intraoperative SSEP changes occurred with noninvasive distraction but were reversible when using 30 pounds of traction. 2PD testing changes were common postoperatively but not correlated to changes in SSEP. Patients with increased 2PD did not have sensory changes detectable on clinical exam or subjective patient history.

Level of evidence: Experimental level II, prospective comparative study.

Keywords: SSEP; ankle arthroscopy; somatosensory evoked potentials.