Determination of Angles of Awkward Wrist Postures for Wrist and Grasp Force

Abstract

Neutral position of the wrist has been recommended because this posture can allow the greatest hand force and avoid musculoskeletal injury or illness. Most postural analyses have categorized wrist positions into three levels such as 0, 15 or 16, and 45 degrees to decide the severity of awkward wrist postures (McAtamney and Corlett, 1993).

The purpose of this study is to verify the change of wrist force with simultaneous grasp force at every two degrees of wrist angle under isokinetic wrist movements at low speeds. Moreover, specific wrist angles may be recommended to define awkward wrist postures in terms of wrist and grasp maximum voluntary contractions.

Twenty-five male subjects voluntarily participated in the study. The wrist and grasp forces were the dependent variables. The independent variables were three levels of speed (10 deg/sec, 20 deg/sec, and 30 deg/sec) and two levels of wrist motions (flexion and extension). Each trial was divided into 2-second exertions to reduce the effect of the forearm fatigue.

With the specially designed isokinetic wrist dynamometer, each subject followed the American Society of Hand Therapists standard (Fess and Moran, 1981) and was tested in a random order with two-minute rest periods between trials.

The results of analysis of variance performed for the wrist force revealed that there were significant differences in angle, speed, and wrist motion (p = 0.0001, p = 0.0001, and p = 0.0001, respectively). According to Tukey tests, the range of angles from 66 degrees of flexion to 26 degrees of extension were in the same grouping that included the maximum wrist force that was 49.674N at 18 degrees of flexion. The mean wrist force of 30 deg/sec (38.4657N) was lower than those of the others (43.2751N for 10 deg/sec and 41.3768N for 20 deg/sec). Also, the mean wrist force of flexion (38.4657N) was greater that that of extension (29.599N).

The results of ANOVA performed for the grasp force showed that there were significant differences in angle and speed (p = 0.0001 and p = 0.0001). Tukey tests showed that the wrist angle from 58 degrees of flexion to 22 degrees of extension was in the same group that included the maximum grasp force that was 285.45N at 24 degrees of flexion. The mean grasp force of the 10 deg/sec (231.025N) were higher than the other speeds (204.931N for 20 deg/sec and 200.215N for 30 deg/sec). Both wrist and grasp forces decreased as the wrist angle deviated far from the neutral position in either direction. The study identified the neutral wrist position range in terms of wrist and grasp forces. According to the results, the wrist position can be divided into three categories. First, the neutral range of the wrist is from 58 degrees of flexion to 22 degrees of extension. Second, a reasonably neutral range can be from 70 to 58 degrees of flexion and from 22 to 70 degrees of extension. Third, awkward posture of the wrist is from 70 degrees flexion to the maximum for that subject and from 70 degrees of extension to the maximum range for that subject. These results broaden the currently accepted neutral range and has major implications for postural analysis and the definition of awkward wrist angles.