Sensitivity was 20 μV/division, low-frequency filter was 20 Hz, high-frequency filter was 2 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). Five sensory nerve action potentials (SNAPs) were recorded, with a bipolar fixed distance (2.2 cm) surface electrode (similar to that used for stimulation) moved in step of 2 cm from a point 2 cm proximal to the distal wrist crease to a point 6 cm distal to this crease (R1–R5). The proximal point (R1) was distal from the stimulating cathode (−) placed at digit III, proximal to the inferior palmar wrist crease. The distal point (R5) 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.

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 12 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 (maximum 20 stimulations). The conduction delay per 2 cm (CD/2 cm) is the time necessary for the nerve impulse to travel a distance of 2 cm between two adjacent recording points. Nerve segments 1 and 4 were considered to be outside the carpal tunnel and nerve segments 2 and 3 inside the carpal tunnel. The segment with the highest CD/2 cm was called the maximal CD/2 cm (MCD/2 cm). The normal CD/2 cm (nCD/2 cm) was the mean CD/2 cm calculated from the two segments (1 and 4) outside the area of compression. Amplitude data was not addressed. Digit III was aligned with the course of the median nerve at the wrist to minimize errors in measurement of distance. Skin temperature was measured, and hands were warmed prior to testing when temperatures were below 32 °C. Normal values (Table 1) were obtained in 50 dominant wrists of 50 control subjects (33 women and 17 men, age range 27–68 years, mean age 43 years). Seror [1] also studied 50 wrists of 41 successive patients with mild CTS (Table 2), 35 women and 6 men (age range 34–82 years, mean age 47 years).