Effect of hand size on the stimulation intensities required for median and ulnar sensory nerve conduction studies.

OBJECTIVES

To examine the effect of hand size on median and ulnar sensory nerve conduction study (NCS) stimulation intensities and pain scores.

DESIGN

Prospective, single group design to compare main outcomes by using a standard distance of 14cm versus the proximal wrist crease in 3 different hand sizes.

SETTING

Electrodiagnostic laboratory in a department of rehabilitation medicine.

PARTICIPANTS

Healthy volunteers (N=25) aged 20 to 30 years.

INTERVENTIONS

Hand size was determined, based on the distance between the proximal wrist crease and the base of the long finger, resulting in 3 groups (≤11cm, >11-12cm, >12cm) with 12 hands per group. Antidromic median and ulnar sensory NCSs were performed. The nerves were randomly stimulated at the proximal wrist crease and 14cm from the recording electrode.

MAIN OUTCOME MEASURES

Supramaximal stimulation intensities and 10-cm visual analog scale (VAS) pain scores at each stimulating site were recorded and compared.

RESULTS

Thirty-six hands from 25 young healthy volunteers were studied. There was no correlation between the body mass index (BMI) and stimulation intensity, and BMI and VAS (r<0.3) in both median and ulnar nerves. Overall analysis showed that the stimulation intensity and VAS at 14cm were significantly greater than at the proximal wrist crease. Subgroup analysis showed the same result in all groups for the median sensory NCS, but in only the small hand group for the ulnar sensory NCS.

CONCLUSIONS

When the same distance is used for NCSs regardless of patient size, smaller individuals required greater stimulation and reported greater discomfort. This may reflect greater nerve depth and suggests that one size fits all may not be the best approach with NCSs.