Comparison of techniques for detecting digital neuropathy.

A complication of endoscopic carpal tunnel release (6/53 consecutive cases) is rupture of a digital branch. The objective of this study was to find a method for detecting neuropathy of the digital branch innervating the radial side of the fourth digit and the ulnar side of the third digit. This study examined whether the following sensory nerve conduction techniques would enhance diagnosis of this neuropathy: (1) recording with standard digital ring electrodes; (2) recording with ring electrodes from two adjacent fingers; and (3) disc electrodes placed between two fingers. Ten healthy individuals were studied before and after lidocaine anesthesia of the digital branch between the ring and middle finger. Statistical analysis was performed with a two-tailed, paired t test. Results show that after lidocaine injection there was a decrease in antidromic amplitude of 94% for ring electrodes on the fourth digit, 62% for rings on the third digit, 77% for disc electrodes between the fourth and third digits, and 74% for rings on digits 4 and 3 (P < 0.005), with no significant change in peak latency (P > 0.3). In conclusion, although all techniques used in this model yielded a significant change in amplitude, rings on the third digit compared with the second and discs between digits 4/3 compared with 3/2 were most specific without false-positives from normal data. It is hoped this study will aid the electromyographer in postoperative diagnosis.