Sensitivity was 20 μV/division, low-frequency filter was 20 Hz, high-frequency filter was 1.6 kHz, sweep speed was 0.5 ms/division, duration of pulse was 0.2 ms, and the machine used was a Dantec Cantata. Rate of pulse was not specified.

This study was performed in the supine position. The forearm, wrist, and hand were stabilized with Velcro on a comfortable board.

Following the orthodromic method [1], the inching test was performed on sensory fibers of the median nerve in digit III (Fig. 1). The sensory potential was recorded with a bipolar fixed distance (2.2 cm) surface electrode (similar to that used for stimulation) moved centimeter by centimeter from a point 2 cm proximal to the distal wrist crease to a point 6 cm distal to the distal wrist crease, providing nine measurements (R1–R9). The proximal point (R1) was distal from the stimulating cathode (−) placed at digit III, proximal to the inferior palmar wrist crease. The distal point (R9) was proximal to the stimulating cathode (−), in the midpalm. The active electrode (A) was placed proximal to the stimulating cathode (−); the reference (R) was placed distally. The ground (G) electrode position was not specified in the report; the figure shows the ground electrode placed on the palm. In this study, the author considered only eight of the ten segments previously studied because in mild carpal tunnel syndrome (CTS), he did not find an abnormal maximal conduction delay per centimeter (MCD/cm) in the proximal two segments. This finding explains the slight difference in the mean and normal conduction delay per centimeter (CD/cm) values compared with the results of the earlier study [2].

The median nerve was stimulated by a bipolar fixed distance (2.3 cm) surface electrode on the proximal interphalangeal joint of digit III (S). The cathode (−) was placed proximally to the active recording electrodes (A); the anode electrode (+) was placed distally at the distal interphalangeal joint. The current was of 0.2 duration and varied from 8 to 15 mA (×2.5 sensory threshold).

Peak latency (ms) was measured from the onset of the stimulus to the peak of the negative deflection of the sensory nerve action potential (SNAP) with an accuracy of 0.02 ms. Averaging was performed when necessary to obtain more precise latencies; typically, 2–10 stimulations per site were sufficient. The conduction delay per centimeter (CD/cm) is the time necessary for the nerve impulse to travel a distance of 1 cm between two adjacent recording points. The normal conduction delay per centimeter (nCD/cm) was the mean CD/cm calculated from segments outside the area of compression. Nerve segments 1–2 and 7–8 were considered to be outside the carpal tunnel and nerve segments 3–6 inside the carpal tunnel. The maximal conduction delay per centimeter (MCD/cm) was defined as the greatest CD/cm value out of the eight CD/cm recorded in each examined wrist. The amplitude data was not addressed. Digit III was aligned with the course of the median nerve at the wrist to minimize errors of distance measurement. The subject’s skin temperatures were measured and hands were warmed before testing for temperatures below 32 °C. Orthodromic (Table 1) and antidromic (Table 2) normal values were obtained in 20 dominant wrists of 20 control subjects (15 women and 5 men, age range 20–67 years). Seror also studied 20 dominant wrists (Table 3) of 20 patients (15 women and 5 men, age range 32–76 years, mean age 47 years) with mild CTS.