Central-Deficit Hand Prosthesis

ROBERT R. CLARK, M.D.


In this industrial age, with the use of a multiplicity of stamping and punch-press-type machines, amputee clinics are being confronted increasingly by a somewhat unique upper-extremity amputation. This amputation consists of loss of the index, middle, and ring fingers with the thumb and little finger maintained intact and uninjured ( Fig. 1 ). Often, portions of the second, third, >and fourth metacarpals and associated structures are likewise lost. In some respects the clinical picture resembles the central congenital deficiency described by Frantz and O'Rahilly1 as terminal longitudinal partial adactylia or partial aphalangia, according to the extent of the loss. The purpose of this paper is to present an approach to the problem of providing a prosthetic replacement for this particularly unique form of limb loss.

Advantages and Disadvantages

As is well known to patients as well as to specialists in the field of amputations, the replacement of a missing limb segment with a prosthesis provides the wearer with both advantages and disadvantages. The advantages are obvious: increased function and improved cosmesis. The disadvantages are loss of the sensations of touch and pain resulting from the covering of the sensitive stump with an insensitive prosthetics material. Use of any form of hardware which covers the intact digits in the fitting of a patient with the described amputation has the distinct disadvantage of rendering the normal little finger and thumb insensitive to touch or pain. In addition, the valuable motion of pinch between the tip of the little finger and the thumb in opposition has been impaired by most attempts to replace the missing digits with a prosthesis. The usual reasoning, therefore, is that the patient is better off with thumb-to-little-finger pinch and sensation than he is with the grip or grasp provided by a prosthesis which interferes with the pinch and sensation of the uninjured fingers.

New Device Developed

With these thoughts in mind, a simple gauntlet type of device was fashioned to fit as a foundation over the dorsal and volar surfaces of the hand but with both the little finger and the thumb left totally free ( Figs. 2 & 3 ). The prosthetic replacement of the three missing fingers is attached to the foundation by a hinge. Each finger can be set passively in the desired amount of flexion. To the ulnar aspect of the prosthetic ring finger is attached a flange into which the little finger can be placed voluntarily in order to provide motor power for the prosthetic digits. This flange consists of a small saddle-shaped metal disc with an "L"-bar which can be screwed to the prosthetic finger ( Figs. 4 & 5 ). The hinge is spring-loaded into an extended position so that when the little finger is voluntarily removed from the niche the prosthetic fingers rest in full extension. The spring used is a single-coil type of 1/16 in. steel wire, approximately ½ in. in diameter, which is stretched across the hinge. This arrangement allows the wearer to continue to use the same thumb-little-finger pinch with sensation that he has without the prosthetic device. When the patient elects to place the little finger in the niche and activate the prosthetic fingers, he then has a full grasping or gripping mechanism similar to that of an active prosthetic hand. No cable device is needed to activate this power since it is provided by the patient's little finger. Opposition provided by the unencumbered thumb is unimpaired. The entire device is then covered by a cosmetic glove with a volar zipper to provide an anchor to the hand stump ( Figs. 4 & 5 ). The cosmetic glove somewhat diminishes but does not eliminate sensation in the thumb and little finger.

Summary

This article presents a design for an active prosthetic replacement for the unique injury involving the loss of the index, middle, and ring fingers. It provides the wearer with cosmesis and grasp or grip without sacrificing totally the sensation and pinch provided by his uninjured little finger and thumb. Our experience with this device at the amputee clinics in Akron has been quite satisfactory. Its use by others faced with a similar problem is recommended.

Juvenile Amputee Clinic Children 's Hospital Akron. Ohio

References:
1. Frantz, C. H., and Ronan O'Rahilly, Congenital skeletal limb deficiencies. J. Bone and Joint Surg., 43-A:8:1202-1224, December 1961.