Prosthetic Pollicization

Robert R. Clark, M.D. Walter A. Hoyt, Jr., M.D.


A wise philosopher once said, "The whale would rule the world if only he had a thumb!" Perhaps the biological accuracy of that philosophical opinion is debatable, but the implication of the observation is well accepted by orthopedists. In the human, the thumb certainly comprises his most important appendage. It is commonly accepted that, at least from a functional point of view, the thumb constitutes at least 50 percent of the hand. The impairment of upper-extremity functioning following complete loss of the thumb is easily within that range.

A recent review of the literature indicates that a myriad of articles have been written about the reconstitution of missing thumbs in amputees, using varying surgical techniques. All agree on the great benefit to the patient of providing a replacement for the missing thumb. The methods described differ to a greater or lesser degree in donor organ, technique of replacement, and criteria of expected result. Some are indeed quite ingenious. Most require multiple surgical procedures in order to achieve the desired end result. Few procedures attain a high percentage of excellent results, with a marked decrease in disability. Almost none of the current procedures presents a simple approach that is appealing to the patient, since all disable him for long periods of time, convalescing from the multiple surgery involved. Because of this disadvantage, our experience with thumb amputees indicates that they tend to shy away from the tedious, time-consuming reconstructive surgical programs that have been devised up to this time, and tend rather to try to live with their deformity and function as best they can minus this important digit.

A further review of the literature illustrates a marked paucity of suggestions for the creation of an artificial thumb or of a prosthetic replacement for the missing part. Bunnell, in his excellent book on hand surgery 1, devotes two pictures and scant description to such a prosthetic replacement of the thumb. In a limited way, the Orthopaedic Appliances Atlas2illustrates such a device but provides only a brief description of the item. The rest of the literature is amazingly devoid of references to such appliances. The reason given is that the insensitivity of the device causes the patient to discard it before he is fully able to appreciate its utility and attain increased function.

This report is intended only as a preliminary presentation concerning such a prosthetic replacement for the thumb. It is not meant in any way to imply the discovery of a new method of replacing thumbs which will revolutionize the prosthetic world. Nor does it even intend to claim any original designs which have been heretofore untried. Rather, the purpose of this paper is to describe a pilot model of a thumb replacement prosthesis which is being worn at the present time by some of our clinic patients. In so doing, we hope to stimulate interest in the development of a more sophisticated device for thumb replacement. Ideas for modifying or revising such a prosthesis will develop only when other clinic teams try such a construction and create new concepts on an empirical basis. The end result of such an approach could be, in our opinion, a highly cosmetic replacement thumb, which would yield such increased function as to override any objections to its insensitivity. As a result, thumb amputees who would otherwise shun the more complicated and time-consuming surgical replacement procedures will be willing to use such a device.

Description

As shown in Fig. 1 and 2 . Fig. 3 . and Fig. 4 , our suggested prosthetic device is designed with a molded plastic base which fits closely around the contours of the proximal portion of the hand and the base of the no longer existent thumb (Fig. 1 and 2 ). The generally flat topography of this area, together with the prominence of the remaining first metacarpal, provides a suitable anchor point for a foundation with good stability. Such a plastic form-fitting mold is readily anchored by a Velcro strap around the wrist. With this reasonably firm foundation, a digit can be constructed to provide an opposing static structure against which the remaining digits can exert flexor force.

The basic thumb unit is a modification of that used on a standard Robin-Aids prosthetic hand. This thumb unit has two positions of abduction that can be set passively (with the other hand) to accommodate large or small objects. In our more recent models, this adjustment has been increased to allow three positions to be set passively. The first is in wide abduction, to allow opposition from the other fingers for grasping objects of about 5 inches diameter (Fig. 1 and 2 ). The narrowest position is in opposition to allow pinch of very thin objects, which accommodates about 50 percent of normal total opposition (Fig. 3 ). The third position is midway between and can be used for glasses or other objects about 3 inches diameter (Fig. 4 ). The purpose of increasing the selection to three positions is obviously to attain more versatility. The technical construction of such an additional position represents very little additional effort.

In our empirical quest for the most versatile prosthetic thumb possible, it was reasoned that at times thumb function would best be carried out if the thumb were not pointed at the index finger, which is the standard direction of deviation. With this in mind, we placed the entire thumb mechanism on a pivotal plate, which permitted two passively adjustable positions (Fig. 5 ). In this manner, the thumb could be directed not only toward the index finger for pinch, but also toward the general mass of remaining fingers to provide a more effective gross grasp. This second position is directed between the middle and ring fingers, so that an object such as a ball may be gripped more effectively. Clinical findings indicate that this provision is advantageous to the wearer.

Conclusions

We have directed our attention toward the development of a useful and versatile replacement for a missing thumb by artificial means. Although this replacement lacks the sensation of a normal or reconstructed thumb, it does provide a myriad of functions unattainable with no thumb at all. It has the obvious advantage that it does not require the multiple procedures of surgical pollicization and the accompanying loss of time for rehabilitation and healing. By mechanical means, multiple positions can be achieved to make such a device quite versatile. It is our hope that this presentation will provide a foundation for continued study and revision. It is postulated that ultimately a prosthetic pollicization unit will be developed which will markedly benefit those amputees who have suffered the loss of this most important digit.

Robert R. Clark, M.D. and Walter A. Hoyt, Jr., M.D. is associated with the Clinic Co-Chiefs Juvenile Amputee Center Children's Hospital Akron, Ohio

References:
1. Bunnell, Sterling, Surgery of the Hand, 4th ed, J.B. Lippincott, New York, 1964. 
2. Orthopaedic Appliances Atlas, Vol. 2:91, J.W. Edwards, Ann Arbor, Mich., 1960.