Motion Analysis of Thumb in Cellular Phone Use

Naotaka Sakai,Satoshi Shimawaki

doi:10.1155/2010/318641

Abstract

The thumb motion of 10 normal subjects during cellular phone use was measured using a reflective marker detection system to compare the maximum, minimum and range of flexion angles of the interphalangeal (IP), metacarpophalangeal (MP) and carpometacarpal (CM) joints. Two micro-reflective markers 3 mm in diameter were each placed on the dorsal surface of the distal phalanx, basal phalanx and metacarpal bone of the thumb. Three markers were placed on the dorsal hand in order to define the dorsal hand plane. Each subject pushed the 12 keys of a folding cellular phone with an 85-mm-long and 40-mm-wide keypad, sequentially from ‘1’ to ‘#’, and the pushing motion was recorded by six infrared video cameras for 12 seconds, using the VICON 612 system. The mean maximum flexion angle of the MP joint was significantly (p< .05) larger than the CM joint, and the mean minimum flexion angle of the CM joint was significantly (p< .01) smaller than the IP and MP joints. The mean range of motion of the IP joint was significantly (p< .05) larger than the MP and the CM joints. In a comparison of different key-pushing motions, only the CM joint was significantly (p< .05) larger in its range of motion. In conclusion, thumb motion on pushing the keys of the cellular phone was produced mainly by the MP and the CM joints. In addition, the ability to reach keys in different areas of the cellular phone keypad is regulated by changing the flexion angle of the CM joint.

Highlights

The cellular phone has brought about a revolutionary change in human communication, and the ongoing development of hand-held micro-mobile computers is certain to cause further change in daily life
Discussion of medical issues related to cellular phones, has focused on the risk of use while driving and on the risk of exposure to the electromagnetic waves they emit (Jokela et al 2004; White et al 2004; Johal et al 2005; Eliyahu et al 2006); there are few references in the literature to hand motion during cellular phone use
Yoong (2005) investigated tenosynovitis in school children who were sending more than 100 text messages per day, and pointed out that a younger than expected group of patients was diagnosed with disorders related to mobile phone use, such as de Quervain’s tenosynovitis

Summary

Introduction

The cellular phone has brought about a revolutionary change in human communication, and the ongoing development of hand-held micro-mobile computers is certain to cause further change in daily life. Yoong (2005) investigated tenosynovitis in school children who were sending more than 100 text messages per day, and pointed out that a younger than expected group of patients was diagnosed with disorders related to mobile phone use, such as de Quervain’s tenosynovitis. The hand motion is quite specific, in that almost all key-pushing movements involve only the thumb, while the other fingers hold the body of the cellular phone. Storr et al (2007) reported a female patient with de Quervain’s tensynovitis from cell phone use, who sent 2,500 texts per month, and stated that the specific thumb movement would cause the tenosynovitis or other overuse trouble around the thumb.

Methods

Results

Conclusion