Sensitivity was 10 μV/division, low-frequency filter was 32 Hz, high-frequency filter was 3.2 kHz, sweep speed was 1–2 ms/division, and rate of pulse was 1/s. Duration of pulse and the machine used were not specified.

This study was performed in the supine position.

Following the orthodromic method [1], signals were recorded using surface electrodes at the wrist from the median and ulnar (R1, R2) nerves from stimulation of digit II and digit V (Fig. 1) and from stimulation of the palmar branches of the median and ulnar nerves (Fig. 2), respectively. For the median nerve (R1), electrodes were placed between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL) muscles (ideally proximal to the distal wrist crease). The active electrode (A) was placed proximal to the distal crease at the wrist, 8.5–11 cm proximal to the stimulating cathode in the palm (S1). The reference (R) was placed 2 cm proximally to the active electrode. For the ulnar nerve (R2), electrodes were placed just lateral to the tendon of the flexor carpi ulnaris (FCU), ideally proximal to the distal wrist crease. The active electrode (A) was placed proximal to the distal crease at the wrist, 8.5–11 cm proximal to the stimulating cathode in the palm (S2). The reference (R) was placed 2 cm proximally to the active electrode. The electrodes for the median and ulnar recordings at the wrist were placed at identical distances from the stimulating sites for the median and ulnar nerves at midpalm level (S1, S2). Recordings of both the median and ulnar nerves (R1, R2) were made at identical distances (range 8.5–11 cm) along the palm (S2) from the palm stimulating sites (S1, S2). The author did not use a fixed distance, preferring a distance range. Ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm. Median (R1) and ulnar (R2) nerve recordings were made separately. Digit–wrist and palm–wrist segments of each nerve are studied separately.

Stimulations were applied to the median and ulnar nerves separately. The median nerve was first stimulated at digit II (S1) using saline-soaked lint-covered silver strips; then it was stimulated in the palm (S2) using a bipolar stimulator with an interelectrode distance of 1.5 cm. For digit II stimulation (S1), the cathode electrode (−) was placed at the base of digit II and the anode electrode (+) over the distal interphalangeal joint of digit II. For palm stimulation (S2), the cathode electrode (−) was placed proximally at the distal skin crease, toward the web between digit II and digit III. The anode (+) was placed distally. The ulnar nerve was first stimulated at digit V (S2) using a saline-soaked lint-covered silver strips; then it was stimulated in the palm (S2) using a bipolar stimulator with an interelectrode distance of 1.5 cm. For digit V stimulation (S2), the cathode electrode (−) was placed at the base of digit V; the anode electrode (+) was placed over the distal interphalangeal joint of digit V. For palm stimulation (S2), the cathode electrode (−) was placed proximally at the distal skin crease, toward the web between digit IV and digit V. The anode (+) was placed distally. Stimulations of both median and ulnar nerves were made at identical distances (8.5–11 cm) along the palm (S2) from the wrist recording sites (R1, R2).

Onset latency (ms) was measured from the onset of the stimulus to the onset of the negative deflection of the evoked sensory nerve action potential (SNAP) or the onset of the first positive peak, if present. Latencies were measured to the nearest 0.05 ms. Peak to peak amplitude (μV) was measured from the peak of the negative deflection to the peak of the positive deflection. No attempt was made to control temperature rigorously, but if the hands of patients or controls were obviously cold, they were warmed for 5 min in water. Distances were measured with a flexible tape and were to the nearest 0.5 cm. Normal values were obtained from 54 median and ulnar nerves of 29 healthy (Table 1) subjects (Group 1, 16 men, age range 19–63 years, and 13 women, age range 19–61 years), and pathological values were recorded in 72 hands (Table 2) from 47 patients (Group 2) referred with the suspected diagnosis of carpal tunnel syndrome (CTS).