Digital Vibration Threshold, Fine Motor Impairment, and Hand Strength in Automobile Manufacturing Workers

摘要

Vibration threshold (VT), a measure of hand sensory nerve function,is associated with segmental vibration exposure and other ergonomic stressors,as well as decreased hand strength. In a study of male automobile manufacturing workers, analyses were conducted to determine: 1. whether those with elevated VTs or fine motor functional impairment (FI) had lower grip or pinch strength, and 2. whether the combination of elevated VT plus FI improved the predictive value of either alone for hand strength. Subjects were surveyed at three time periods: baseline (TO) ( n = 988),one year (Tl) ( n = 664) and six-year (T2) ( n = 409) follow-up. Bilateral second and fifth digit VT norms at 120 Hz were established from the subjects ( n = 95) with self-reported low exposure to ergonomic stressors. Abnormal VTs were defined as greater than two standard deviations from the age-adjusted norms at T0. FI was defined as difficulty in buttoning clothing and/or picking up small objects at T0. Hand strength means were compared ( t -test) between VT normal and abnormal subjects,and also for those with and without FI. At T0,subjects with elevated fifth digit VTs compared with normal subjects had small but statistically significant bilateral decrements in pinch strength and reduced right grip strength. Right second digit VTs were similarly associated with reduced grip and pinch strength. However, these associations were not seen prospectively. Among workers with abnormal FI at baseline, the associations were stronger and more consistent. Yet those with both FI and elevated VT demonstrated even greater mean hand strength differences. Both at T0 and Tl ,grip and pinch strength were 20%～30% lower in these subjects (with elevated VT in either digit, all P < 0. 05 ). At T2 only, grip strength was reduced in those with fifth digit nerve impairment (R: 23.2 vs .21.2 kg,P = 0.06; L: 23.4 vs .20.8 kg,P< 0.05),and not similarly reduced in those with T0 FI only. VT,in combination with upper extremity FI,may be predictive of decreased hand strength. Further analyses will examine the pattern of upper extremity signs and symptom in these workers.