Effect of grip type, wrist motion, and resistance level on pressures within the carpal tunnel of normal wrists

Abstract

Elevated carpal tunnel pressure (CTP) has been associated with carpal tunnel syndrome. This study systematically evaluated the effect of wrist motion resistance and grip type on CTP during wrist motion typical of occupational tasks. CTP during four wrist motion patterns, with and without resistance, and with and without gripping, was measured in vivo in 14 healthy individuals. CTP measured during compound motions fell between that measured in the cardinal planes of wrist flexion/extension and radial/ulnar deviation. Generally, with no active gripping there was little pressure change due to wrist angular displacement or resistance level. However, concurrent active pinch or power grip increased CTP particularly in motions including extension. CTP typically did not increase during wrist flexion, and in fact often decreased. Extension motions against resistance when employing a pinch or power grip increase CTP more than motions with flexion. Results could help inform design or modification of wrist motion intensive occupational tasks. © 2014 The Authors.

Keywords: carpal tunnel syndrome; in vivo; pinch; power grip.

Figure 1

(a) The No-grip handle showing finger guard for finger positioning, (b) Pinch grip handle with a pinch pulp grip, and (c) The Power grip handle.

Figure 2

A photograph illustrating the four wrist motion condition: CM1—extension + radial deviation, and flexion + ulnar deviation, similar to a dart throwing motion; E/F—extension and flexion, CM2—extension + ulnar deviation, and flexion + radial deviation; R/U—radial and ulnar deviation.

Figure 3

The experimental apparatus detailing the pivot and lock mechanism for adjusting the handle orientation, the magnetic particle brake that provides resistance to clockwise and counterclockwise motion about the axis aligned with the wrist, and the potentiometer that measures wrist angular displacement. The dashed vertical line illustrates alignment of the particle brake shaft with the wrist center of rotation.

Figure 4

Carpal tunnel pressure (y-axis) versus wrist angular displacement (x-axis), each graph with a family of curves of resistance levels. By rows: Pinch Power and No-grip applications. By column, wrist motion conditions, left to right: (CM1)—extension/radial deviation & flexion/ulnar deviation, (E/F)—extension & flexion, (CM2)—extension/ulnar deviation & flexion/radial deviation, (R/U)—radial deviation & ulnar deviation. Sold-filled symbols indicate values significantly different from the neutral no-load condition.