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Effect of Tourniquet-Related Nerve Ischemia on Response to Handheld Nerve Stimulation in Ulnar Nerve Transposition
Tony Y Lee, BA1; Yosita P Beamer, MBS1; Christopher J Dy, MD1; David M Brogan, MD, MSc2
1Washington University in St. Louis, St. Louis, MO; 2Washington University School of Medicine, St. Louis, MO

Introduction Tourniquet-related nerve ischemia has been well studied in trauma and several common orthopedic procedures. However, in ulnar nerve transposition for cubital tunnel syndrome, the effects of shorter tourniquet times on smaller nerves in the upper extremity are not well understood. The purpose of this study is to determine the timing of ischemia-induced changes during transposition and better understand the relationship between nerve stimulation and preoperative assessment (clinical, electrodiagnostic, sonographic). Our hypothesis is that tourniquet-related ischemia of the ulnar nerve will not be significant enough to demonstrate a detectable decrease in response to a handheld nerve stimulator at time intervals of 15, 30, and 45 minutes.
Materials and methods We identified 20 patients undergoing ulnar nerve transposition who received standard preoperative assessment of their neuropathy. Preoperatively, a tourniquet was placed on the upper extremity and inflated. Intraoperative nerve stimulation was performed using a Checkpoint Guardian Nerve stimulator to assess the minimum amplitude and frequency needed to elicit muscle response at three 15-minute intervals from initial tourniquet time. Secondary outcome measures completed preoperatively included: ulnar nerve ultrasound, nerve conduction studies, needle electromyography, static 2-point discrimination, lateral and tip pinch, as well as manual testing of the first dorsal interosseous. A survey for demographic and symptom severity data was completed following consent.
Results The changes in threshold amplitude and frequency were calculated between timepoints (??30-15, ??45-30, ??45-15); the mean changes were not found to be statistically significant (P-values 0.64 and 0.078) in ANOVA. There was no association between preoperative ulnar nerve to ADM compound muscle action potential and average intraoperative threshold amplitude, but a moderate negative correlation was observed with threshold frequency (R=-0.52, P=0.018). Ulnar nerve diameter was moderately associated with initial frequency at 15 min, but it was not significant (R=0.4, P=0.16).
Conclusions Across three timepoints during ulnar nerve transposition, no considerable change was present in either threshold amplitude or frequency following tourniquet placement. Thus, reduced perfusion due to tourniquet placement does not appear to significantly impact nerve conduction in the first 45 minutes of tourniquet use. In addition, intraoperative nerve stimulation can provide meaningful information that correlates with preoperative testing.


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