A Child's Dynamic Wrist-Extension-Assist Splint

BY BARBARA BENEN DEMCHLCK, O.T.R.* St. Agnes Hospital Children's Unit, White Plains, New York* Occupational Therapy Supervisor


A dynamic wrist-extension-assist splint has been attached to a standard lumbrical bar for a 4-year-old girl with wrist and hand weakness secondary to spinal muscular atrophy. Splints are currently being worn on both hands, providing improved position and enhanced functional ability.

A Case History

Although this child's disease has been present since birth, fine motor function remained relatively unimpaired until she was 3 an 1/2 years of age, at which time weakness of lumbrical and interosseous muscles was detected in both hands. Metacarpophalangeal (MCP) joints were frequently postured in hyperextension, and the child had difficulty sustaining grasp on an object. She was fitted with bilateral lumbrical-bar splints to provide support at the MCP joints, thereby allowing long finger flexors to function at their optimum.

The lumbrical bar, or dorsal metacarpal splint, as illustrated in the Manual on Static Hand Splinting1, consists of three interconnected orthoplast bars. Two are on the dorsum of the hand, with one proximal and the other distal to the MCP joints. The third is a volar bar, conforming to the transverse palmar arch of the hand. This splint design was modified slightly by shortening the palmar bar and attaching a strap from it to the ulnar side of the dorsum of the splint. This change was made to facilitate donning and removing the splints, since several individuals such as teachers, aides, and parents would be putting them on and taking them off.

When the child was first introduced to the splints, they were referred to as bracelets. The youngster was given the opportunity to decorate her "bracelets" with plastic stickers, an activity which she enjoyed. When they were completed, she readily wore the splints, proud to display her work. Taking part in designing her splints aided the child in accepting them and participating in the therapeutic regime.

Several months later, significant wrist-extensor weakness was noticed. On a manual muscle test, wrist extensors were graded fair minus. Ulnar extensors were slightly stronger than radial extensors; and consequently the child was frequently postured in ulnar deviation as well as in flexion, both at rest and during activity (Figure 1) . Previously published splint designs2,3 could not stabilize the MCP joints and at the same time accommodate the discrepancy between ulnar and radial wrist extensor strength in this patient. Therefore, a dynamic splint, which would attach to the lumbrical bar, was devised to assist the weak wrist extensors and to counteract the pull into ulnar deviation.

A volar shell for each forearm was molded of orthoplast and secured to the child's arm with two Velcro straps. The shell began just proximal to the wrist and was approximately two-thirds the length of the forearm. Two sewing hooks were glued to the middle of each shell. A sewing hook was likewise fastened to each side of the dorsum of both lumbrical bars. A rubber band was attached from each hook of the forearm shell to a corresponding hook on the lumbrical bar. Rubber bands were arranged to place more tension on the radial side of the splint than on the ulnar side (Figure 2) .

Tolerance for the splint was developed gradually, and the splint has now been used successfully for several months. It is worn most of the time, except for rest periods and some therapy activities. The child continues to cooperate in wearing the splint, and actively assists in donning and removing it. The tension on the rubber bands has easily been adjusted to match the day-to-day variations in the patient's status, and it is felt that tension could accommodate sonic loss in actual wrist extensor strength.


Cosmetic and functional improvements have been obtained through the use of this splint. With splint donned, resting hand position is with wrist and MCP joints in a neutral position. Full straight wrist extension can be achieved and held against gravity. Grasp strength is increased from 70 to 85 grams on the left and 65 to 82 grams on the right. Prehension of an object is maintained for longer periods, and fatigue during fine motor activities is much reduced. The child uses her preferred left hand for most writing and coloring tasks, whereas without splint application, frequent hand switching is seen. Subjectively, the youngster reports, "It's easier to do things." (Figure 3)

Although it has been used with only one patient, this splint, or an adaptation of it, might be effectively utilized in other cases where weakness of the wrist and hand is present.



  1. Malick, M. H., Manual on Static Hand Splinting. Harmarville Rehabilitation Center, Pittsburgh, 1976.
  2. Malick, M. H., Manual on Dynamic Hand Splinting with Thermoplastic Materials. Harmarville Rehabilitation Center, Pittsburgh, 1974.
  3. De Vore, G., E. Denny, and J. N. Parker, Hand Splints. The Hand Rehabilitation Center, University of North Carolina, Chapel Hill.



Appreciation is expressed to Cynthia C. Rocco for the photographs and to Debra Grosso for the illustration.