Elbow, Wrist, Palm – Digit II

and Mario Di Napoli¹

(1)

Neurological Service, S. Camillo de’ Lellis General Hospital, Rieti, Italy

Original Settings

Sensitivity was 20 µV/division, low frequency filter was 20 Hz, high-frequency filter was 2 kHz, sweep speed was 0.2, 0.5 and 1 ms/division, and the machine used was a specially designed designed amplifier with short blocking time (1 ms) and a low noise (0.5 µV RMS at bandwidth of 2 KHz). Duration and rate of pulse were not specified.

Position

This study was performed in the supine position.

Recording

Following the antidromic method [1], signals were recorded from digit II (index finger) using ring electrodes (Fig. 1). The active electrode (A) was placed around the proximal interphalangeal joint of digit II; the reference (R) was placed on the distal interphalangeal joint of the same finger. Ground (G) electrode was placed around the forearm (author used a Velcro strap).

Fig. 1

Antidromic sensory nerve action potentials (SNAPs) recorded to digit II; stimulation of the elbow (upper trace), wrist (middle trace), and on the palm (lower trace)

Fig. 2

Antidromic sensory nerve action potentials (SNAPs) recorded to digit II, stimulation of the wrist (upper trace) and on the palm (lower trace)

Stimulation

The median nerve was stimulated using surface electrodes at three [2] points along its course: at the elbow (S1), at the wrist (S2), and on the midpalm (S3). At the elbow (S1), shocks were applied on the anterior surface of the upper arm over the brachial pulse. For stimulation at the wrist (S2), the cathode was one [1] cm proximal to the distal crease on the volar surface. The terminal portion of the median nerve was stimulated at midpalm (S3) over the second carpometacarpal space. The anode was proximal. Shock intensity was gradually advanced until a further increase no longer altered the size of the sensory potentials. The voltage required to activate a maximal response was generally similar at different sites of stimulation. At least four trials were given at each stimulus site to confirm the consistency of the recorded response. Using the same points of stimulation, the author performed a motor conduction study to the abductor pollicis brevis (APB) muscle (see motor conduction studies).

Measurements

Onset latency (ms) was measured in steps of 0.1 ms from the stimulus artifact to the onset of the initial negative response (upward deflection). The negative peak amplitude (μV) was determined from the baseline to the negative peak of the sensory nerve action potential (SNAP). The surface distance between the two stimulus sites at the wrist and palm was carefully measured in mm with a ruler. Sensory nerve conduction velocity (SNCV) in the wrist to palm segment was determined according to the conventional formula, dividing the distance by the latency difference between the two evoked potentials. Skin and room temperatures were not controlled. Normal values were obtained from 50 hands (Table 1) of 25 subjects (8 healthy volunteers and 17 patients with unrelated disorders, 13 men and 12 women, age range 15–58 years, average age 36 years). Kimura studied also 20 symptomatic hands (Table 2) from 13 patients with carpal tunnel syndrome (CTS), 14 hands from 7 patients affected on both sides, and 6 hands from the remaining patients with unilateral disease, 3 hands on the right and 3 on the left (3 men and 10 women, age range 38–59 years, average age 47 years).

Table 1

Normal values [1]

Palm–digit II segment	Mean ± 2 SD
Onset latency (ms)	1.34 ± 0.31
SNCV (m/s)	59.9 ± 9.2
Negative peak amplitude (μV)	41.8 ± 21.7

Wrist–digit II segment	Mean ± 2SD
Onset latency (ms)	2.47 ± 0.39
Latency difference (ms)	1.21 ± 0.21
SNCV (m/s)	58.7 ± 7.5
Negative peak amplitude (μV)	38.6 ± 18.7

Elbow–digit II segment	Mean ± 2SD
Onset latency (ms)	6.40 ± 0.77
Latency difference (ms)	3.90 ± 0.50
SNCV (m/s)	62.4 ± 5.7
Negative Peak amplitude (μV)	23.4 ± 9.2

Limits of normal	Values
Wrist–digit II, onset latency (ms)	3.3
Wrist–palm, onset latency (ms)	1.5
Elbow–wrist, SNCV (m/s)	51
Wrist–palm, SNCV (m/s)	44

Table 2

Pathological values [1]

Palm–digit II segment	Mean ± SD
Onset latency (ms)	1.32 ± 0.23
SNCV (m/s)	59.6 ± 8.6
Negative peak amplitude (μV)	30.3 ± 16.4

Wrist–digit II segment	Mean ± SD
Onset latency (ms)	2.90 ± 0.57
Latency difference (ms)	1.58 ± 0.49
SNCV (m/s)	44.9 ± 11.8
Negative peak amplitude (μV)	28.5 ± 13.2

Elbow–digit II segment	Mean ± SD
Onset latency (ms)	6.79 ± 0.68
Latency difference (ms)	3.90 ± 0.37
SNCV (m/s)	58.6 ± 7.4
Negative peak amplitude (μV)	18.0 ± 6.6

Comment

In each hand, Kimura [1] recorded the SNAPs from the second digit after stimulation of the median nerve at the palm, wrist, and elbow. The wrist to palm and palm to digit II latencies were the same in healthy subjects whether tested antidromically as in the author’s study or orthodromically, as was done by Buchthal, Rosenfalck, and Trojaborg [3]. In agreement with these authors, Kimura found slowing along the median nerve sensory fibers from the wrist to palm in patients with clinical signs and symptoms of CTS when conduction time from the wrist to digit was normal. For author, as a diagnostic test, therefore, the sensory fibers may be studied antidromically or orthodromically in assessing the wrist to palm and palm to digit segments of the median nerve.

Kimura [2] in 1979 performing the same antidromic method to digit II studied 122 hands (Table 3) from 61 patients (26 men and 35 women, age range 15–50 years, average age 43 years) with complaints unrelated to the CTS and 172 hands (Table 4) from 105 CTS patients (32 men and 73 women, age range 20–78 years, average age 48 years). Each patient was tested on both sides, but the clinically affected hands were analyzed separately from the asymptomatic hands. There were 172 asymptomatic hands, 134 from 67 patients affected bilaterally and 38 from the remaining patients with unilateral disease, 29 on the right and 9 on the left.

Table 3

Normal values [2]