Analysis of a New Artificial Muscle Type Dynamic Orthosis for Wrist Joint Disease Using a Three-dimensional Motion Analyzer

Abstract

Objectives: Recently, the dart-throwing motion (DTM) has attracted attention as a functional direction of wrist joint motion. Consequently, we devised a new artificial muscle-type dynamic orthosis (Dynamic Traction Splint by Artificial Muscle, DTSaM) to reproduce DTM. This study analyzed the automatic motion of the wrist joint using a three-dimensional motion analysis system to assess how closely the DTSaM replicates DTM.

Methods: The DTSaM orthosis incorporates two McKibben-type rubber artificial muscles, and measurements were performed using image analysis software and a three-dimensional motion analysis system. The wrist radial angle (WRA) was defined as the angle between the line connecting the head of the index finger metacarpal to the radial styloid process and the line connecting the radial styloid process to the lateral epicondyle of the humerus. WRAs were investigated from 60° of palmar flexion to 60° of dorsiflexion.

Results: For dorsiflexion, comparisons of radial deviation and wrist ulnar angle (WUA) between the motion obtained using the DTSaM orthosis and active DTM showed a significant difference (P <0.05) at 30° and 60°, respectively. For palmar flexion, the same comparison showed a significant difference for both the ulnar and radial deviations (30°, P <0.05; and 60°, P <0.01, respectively). Furthermore, WUA showed a significant difference at 50° (P <0.05). Intraclass correlation coefficient analyses yielded good reliability with an average value of ≥0.8.

Conclusion: The DTSaM orthosis produces a motion similar to the DTM. It is hoped that the use of the DTSaM orthosis will help to shorten the treatment period for patients with wrist disease.

Keywords: dart-throwing motion; hand therapy; motion analyzer; wrist joint angle.

Fig. 1.

Essential parts of the DTSaM wrist orthosis: ① forearm cuff (made by Daiya Industry Co., Ltd., Japan), ② hand cuff (made by Daiya Industry Co., Ltd., Japan), ③ artificial muscle for palmar flexion (two), ④ artificial muscle for dorsiflexion (two), and ⑤ controller.

Fig. 2.

Wrist orthosis mechanism for (A) wrist palmar flexion and (B) dorsiflexion. (A) For palmar flexion, the finger cuff for flexion was attached to the middle and ring fingers and the wrist cuff was also attached. The pneumatic artificial muscle (PAM) was attached from the finger cuff to the lateral epicondyle of the humerus. When the PAM contracted, palmar flexion movement was performed, and the dart-throwing motion was reproduced. (B) The artificial muscle expands and the dorsal stay of the wrist joint restricts the movement of the carpal bone and presses the carpal bone in the volar direction. Thereby, traction is added to the metacarpal bone, and traction and dorsiflexion of the wrist joint are performed.

Fig. 3.

Definition of wrist angles for measurement. (A) Wrist radial angle (WRA): the angle formed by the line connecting the index finger head of the metacarpal bone to the styloid process of the radius and the line connecting the lateral epicondylus of the humerus to the styloid process of the radius. (B) Wrist ulnar angle (WUA): the angle formed by the line connecting the little finger head of the metacarpal bone to the styloid process of the ulna and the line from the lateral epicondyle of the humerus to the styloid process of the ulna. (C) Radial deviation (RD): the angle between the line connecting the index finger metacarpal head to the styloid process of the radius and the line connecting the styloid process of the radius to the styloid process of the ulna. (D) Ulnar deviation (UD): the angle between the line connecting the little finger head of the metacarpal bone to the styloid process of the ulna and the line connecting the styloid process of the ulna to the styloid process of the radius.

Fig. 4.

Changes in anatomical angles in the dorsiflexion direction for WRA in the range 10°–60°: (A) wrist ulnar angle (WUA), (B) ulnar deviation (UD), and (C) radial deviation (RD). Analysis of variance and the Friedman test were performed. A post-hoc test was performed using Scheffe’s multiple comparison test. *P<0.05, †P<0.01. ROM, range of motion.

Fig. 5.

Changes in (A) WUA, (B) UD, and (C) RD in the palmar flexion direction for WRA in the range 10°–60°. Analysis of variance and the Friedman test were performed. A post-hoc test was performed using Scheffe’s multiple comparison test. *P<0.05, †P<0.01.