A Temporary Thumb Prosthesis

MILDRED C. EY, B.S., O.T.R., F.A.O.T.A. SHEREE HELFGOTT, B.S., O.T.R.


Case Study

B.S., 53-year-old female, sustained an amputation of the left thumb 1 .0 cm (.39 in.) proximal to the distal end of the first metacarpal while working in a commercial laundry. She was not referred to our facility until seven months later, at which time she was referred for occupational therapy to increase strength and dexterity of her left hand. Following evaluation, it was determined that the residual metacarpal was inadequate for function and that a temporary prosthesis might be helpful until a definitive prosthesis could be obtained. The temporary device was prescribed and fabricated according to the method described below, and was applied a week later. With the prosthesis, the patient is able to obtain a two-point and three-point pinch for manipulation of small and medium-sized objects of various shapes and weights ( Figure 1 and Figure 2 ). The patient finds it particularly useful in some of her needlework hobbies.

The patient was seen in Amputee Clinic two months later. At that time she reported almost daily use of her prosthesis, primarily when she needs it as an assist for fine activities. It is not secure enough for lifting heavy objects. She does not wear it for "dress occasions" and felt that she would like to have a conventional type of prosthetic thumb. The reaction of the prosthetists was that a conventional thumb really would not look or function much better than what she has. Because of the nature of the amputation, a strap would be necessary to hold it in place unless a full glove were used. A full glove would be too restricting to the function of the residual hand.

Two months later B.S. received a definitive "conventional" cosmetic prosthesis. She is very pleased with the appearance and says she will wear it for "dress." For function, however, she prefers the temporary prosthesis.

Fabrication

A model is selected with hands slightly smaller than those of the patient. The model and the therapist apply lotion to their hands before fabrication begins for ease of handling material, and for removal of material from the model.

A 12.7 x 12.7 cm (5 in. x 5 in.) piece of 0.32 cm (1/8 in.) Aquaplast® is used. The initial step is to punch a 0.32 cm (1/8 in.) hole slightly off center toward one corner. The material is then heated in a 60 degree C (140 degree F) water bath with frypan guard in place until the plastic is clear. The therapist then very carefully stretches the material over the left thumb of the model, positioning the hole over the pad on the palmar surface of the distal phalanx and stretching the plastic well into the palm. The model then "shakes hands" with the therapist to obtain functional position of the thumb. When nearly set, the prosthetic thumb is removed from the model, and the edges are trimmed along the line of the thenar crease, continuing around the dorsal aspect of the hand to the proximal end of the first metacarpal. Allow 0.64 cm (1/4 in.) extra for final trimming to fit the patient. Next, cut a piece of nonslip plastic material (i.e., Dycem®) 0.32 cm (1/8 in.) larger than the hole and inset this from inside the "thumb" over the hole. Cut a piece of 0.16 cm (1/16 in.) Aquaplast® 0.32 cm (1/8 in.) larger than the covering, heat the Aquaplast®, and use it to secure the nonslip material in place. When inserting this piece, be careful not to destroy the contour of the thumb. Then, fill the "thumb" with any soft material. At base of the "thumb," apply a piece of heated Aquaplast® to secure the filling. The residual metacarpal on the patient is then covered with heated Aquaplast® and fitted into the prosthesis to mold the socket. Do final trimming and slightly flare the edges. To finish the prosthesis, cover the nonslip surface with masking tape and spray the outside of the prosthesis with flesh-colored enamel. When the enamel is dry, remove the masking tape. A 1.27 cm (1/2 in.) Velcro® strap, long enough to go around the wrist and form a figure-8 when attached to the prosthesis, is then applied. (Beige Velcro® is used because it blends well with flesh tones.) A "keeper" is riveted to the middle of the dorsal edge using a 2.54 cm (1 in.) piece of Velcro® pile. Stainless-steel "speedy" rivets are used. The rivet hole is punched in the Aquaplast® with a small soldering iron, as is the hole in the Velcro®. The long portion of the strap is Velcro® pile with a 5.08 cm (2 in.) section of Velcro® hook fastened to the end which will attach through the keeper. The other end is then riveted to the middle of the thenar-crease edge. If desired, nail polish can be applied ( Figure 3 and Figure 4 ).

Conclusion

A technique for fabrication of a temporary thumb prosthesis has been described. Because of its simplicity, it is conceivable that this or a similar method could be used for temporary replacement of other digits and, in fact, for larger components.

Aquaplast® was the material selected because of its extreme moldability, and thus the ability to achieve fine contours and an intimate fit. It also retains a fair amount of rigidity even when stretched thin, It has, at this writing, held up for several months with little evidence of wear.