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Options for Finger Prostheses

John W. Michael, MEd, CPO
Horst Buckner, MDT, CDT

ABTRACT

Introduction

Finger and partial-finger amputations are some of the most frequently encountered forms of partial-hand losses (1). Although the most common causes of these amputations are traumatic injuries, congenital absences or malformations may present similar clinical challenges (2). Because any of the fingers may be affected in whole or in part, prosthetic restoration is often difficult. This is particularly true when multiple fingers are involved (3).

Clinical Problem

Although the impact is sometimes minimized in earlier literature, loss of even one finger produces significant functional deficiencies. The more dexterous individuals suffer the greatest degree of impairment: A professional musician missing even a portion of one phalanx is significantly disabled. A prosthesis can often restore near-normal function in distal phalangeal amputations (4). If at least one centimeter of mobile phalanx remains, some restoration of active grasp is feasible (see Figure 1 ). The longer the residual finger, the more secure the resulting grip.

In addition to immediate loss of grasp strength and security, finger absence also may cause marked psychological trauma. Although the intensity of this trauma varies among individuals, the psychological impact is not related to the magnitude of amputation (5). Beasley has noted that individuals who keep their hands hidden inside pockets due to embarrassment over appearance are as functionally disabled as a forequarter (scapulothoracic) amputee (6).

Individuals who desire finger replacement usually have high expectations for the appearance of the prosthesis. Although generic replacements can be made using donor molds in specialized central fabrication facilities, the polyvinyl chloride material generally used is easily and permanently stained by such common materials as ballpoint pen and newspaper ink and has not proven durable enough for active use (7). As a result, the rejection rate for these devices is quite high.

Prosthetic Solution

The acceptance rate has been much higher when an individually sculpted custom restoration using silicone elastomer is provided (8). Using a lost-wax technique, a three-piece mold can be used to fabricate a prosthesis that provides an excellent appearance, particularly when individually colored by an artist while the patient is wearing it (9). Multiple layers of clear silicone over each layer of color add a lifelike translucency and protect the coloration from environmental damage.

Fabric reinforcements sandwiched between layers of silicone add significant tear resistance and allow thin, nearly transparent margins. Careful modification of the positive model enhances the overall result. For example, tension reductions enhance suspension and allow adequate silicone thickness without creating a bulky external appearance. Sculpting the wax overlay to be very thin at the finger joints minimizes the restriction in flexion from the silicone restoration.

The overall durability and stain resistance of silicone is far superior to any other material currently available for finger restorations. Almost all stains, including ballpoint ink, newsprint, clothing dyes and food colorings, can be removed easily with water and soap.

Silicone finger restorations may have additional functional benefits. Many traumatic amputees experience painful hypersensitivity at the termination of finger remnants. The gentle, constant pressure of an elastomer prosthesis can help desensitize and protect the injured tip (10). The authors have noted that, over time, scar tissue contained within a silicone prosthesis seems to become more pliant and comfortable. Similar observations have been reported in the medical literature although no conclusive proof has been established (11, 12,13). Recent literature speculates that silicone gel improves the hydration of the stratum corneum of immature hypertrophic scars (14).

While most finger restorations extend to the metacarpal-phalangeal joint so that margins of the prosthesis may be hidden under a decorative ring, long remnants allow for a prosthesis that terminates at the proximal or distal interphalangeal joint. The advantage is relatively unobstructed finger flexion. However, skin color changes due to the seasons, varying light sources and blood circulation may make the transition to this type of restoration more detectable (see Figure 2 ).

Placing a wide ring over the margin of a finger prosthesis ending at the metacarpal-phalangeal joint will make the changing color of the hand less noticeable although the distal joint functions will be slightly restricted. To maintain a natural appearance, the prosthesis is sculpted with each joint slightly flexed. For very short remnants, pliable wires may be inserted into the silicone to allow a change in curvature for typing, writing and similar functions (see Figure 3A ).

Careful coloration is crucial for maximal patient acceptance. Ideally, coloring will be done while the patient is wearing the prosthesis, under a variety of light sources. Satisfactory results are possible when the prosthesis is painted to match a color-true photograph of the patient's hand.

Fingernails may be molded from the base silicone material and pigmented to match the patient's natural nails. Although fingernail polish may be applied to silicone nails, it will last only for one day. Patients who always paint their fingernails will be better served by incorporating prefabricated acrylic nails into the restoration. For maximum versatility, custom acrylic nails can be casted with integral half moons, white margins and other details. Custom nails can also be painted with nail polish when desired (see Figure 3B ).

The superb elasticity of silicone elastomer, combined with the intimate fit made possible by using a rectified positive model of the amputation site for the male mold, makes suction retention the preferred mode of suspension. It is possible to enhance retention further by scraping grooves into the positive model, creating separate vacuum chambers (15). Vaseline should be used to lubricate the skin to facilitate donning and doffing of the prosthesis.

As with more familiar lower-limb amputations, the longer the remaining bony segment, the better the control of the prosthesis. The most challenging cases are those where suction suspension is not feasible.

When suction is marginal because of a short or fleshy residual finger, medical adhesive may be used to hold the prosthesis in situ. The buildup of old adhesive must be removed periodically. Since adhesive suspension is somewhat tenuous, such restorations can only provide passive cosmesis.

When portions of adjoining fingers are missing, as is common in traumatic injury, the prostheses can be joined at the base to help stabilize the prosthesis for the shorter amputation or ablation (see Figure 4 ). If the middle and index fingers require prostheses, even if the middle finger is totally ablated, the entire assembly can be suspended by a decorative band placed on the ring finger. A retention assembly, anchored into the prosthesis, is soldered to the ring (see Figure 5 ). Medical adhesive may be applied to the base of the restoration to help reduce the gap between skin and prosthesis.

Figure 6 shows an alternate solution for a totally ablated finger using a thin, reinforced silicone covering over the adjacent, uninjured little finger for improved suspension. The large stone in the decorative ring camouflages the base of the prosthesis while a retention wire attached to the ring on the uninvolved middle finger adds stability.

When both the ring and little fingers are missing, a decorative ring on the middle finger plus a thin reinforced silicone extension onto the metacarpals may be used. The extension may be enlarged to compensate for more extensive amputations. Medical adhesive is required to stabilize the metacarpal extension (see Figure 7 ).

Thumb prostheses are challenging due to the mobility and stability required. Interphalangeal amputation may permit suction suspension; more extensive loss requires a metacarpal extension and the use of medical adhesive. Pinch resistance in this case will be minimal (see Figure 8 ). A work prosthesis to replace partial thumb loss must extend onto the hand for added stability. When all or most of the thumb is gone, a pliable wire insert will strengthen the extension and increase the range of possible functions.

It is rarely necessary to cover the entire hand with a prosthesis in cases of isolated finger loss. However, when multiple fingers are missing, extensive skin coverage must be considered. Many men prefer a partial-hand prosthesis for multiple finger loss, with the uninjured fingers left free, because they can apply more force and use the hand for a variety of activities. Most women with the same amputation will prefer single finger prostheses even when grasp is reduced and it is necessary to use adhesive to supplement the suspension. These considerations must be discussed with the patient prior to designing the restoration.

Although Pillet advocates fitting each patient with two prostheses pigmented for summertime and wintertime use, we have rarely found this necessary (16). Using a sunlamp or commercial tanning lotion on the hand during the winter months minimizes the loss of summer coloration. Minor coloring differences can be masked by cosmetics.

Conclusion

Good suspension alone is not sufficient for patient acceptance of finger prostheses. For many patients, a high level of cosmesis is paramount. Characteristics such as a pleasing shape, thin margins, lifelike fingernails, and realistic color, contours and detail are also essential for patient satisfaction. This level of restoration is most successful when finger prostheses are individually sculpted and colored in situ under a variety of lighting conditions.

John W. Michael, MEd, CPO, is director of professional and technical services for Otto Bock USA, 3000 Xenium Lane N., Minneapolis, MN 55441. He recently wrote a chapter on "Prosthetic & Orthotic Management of Partial-Hand Amputation" for the Atlas of Limb Prosthetics, Second Edition (C.V. Mosby, 1992).

Horst Buckner, MDT, CDT, is president of Life-Like Laboratories, 2718 Hollendale Lane, suite 400, Dallas, TX 75234. He has more than two decades of experince in creating custom masillofacial and somatorestorations from silicone elastomers and has lectured throughout the world on this topic.

References:

1. Pillet J. The aesthetic hand prosthesis. Orthop Clinics in North Amer 1981; 12;961-70.
2. Beasley RJ. General considerations in managing upper-limb amputations. Orthop Clinics of North Amer 1981;12:4:743-9.
3. Bunnell S. The management of the nonfunctional hand-reconstruction versus prosthesis. Artificial Limbs 1957;4: 1:76102.
4. Pillet J. Partial-hand amputation-aesthetic restoration. In: Bowker JH, Michael JW [eds]. Atlas of limb prosthetics: surgical, prosthetic and rehabilitation principles. St. Louis: CV Mosby, 1992: 227-35.
5. Pillet (1981) Op cit. 961.
6. Beasley (1981) Op cit. 744.
7. Michael J. Partial-hand amputation: prosthetic and orthotic management. In: Bowker JH, Michael JW [eds]. Atlas of limb prosthetics: surgical, prosthetic and rehabilitation principles. St. Louis: CV Mosby, 1992: 217-26.
8. Buckner H. Cosmetic hand prostheses- a case report. Orthotics and Prosthetics 1980;34:3:41-5.
9. Engelmeier RL. A technique for prosthetic nipple restoration: technical note. Orthotics and Prosthetics 1987;40:4:59-62.
10. Livingstone DP. The D-Z stump protector. Amer J Occu Ther 1988;42:185-7.
11. Ohmori S. Effectiveness of silastic sheet coverage in the treatment of scar kebid. Plas Surg 1988;12:95-9.
12. Quinn KJ. Silicone gel in scar treatment. Burns 1987;13:533-40.
13. Wessling N, Ehleben CM, Chapman V, et al. Evidence that use of a silicone sheet increases range-of-motion over burn wound contractures. J Burn Care and Rehab 1985;6:503-5.
14. Burkhardt A, Weitz J. Oncologic applications for silicone gel sheets in soft-tissue contractures. Amer J Occu Ther 1990;45:5:460-2.
15. Herring HW, Romerdale EH. Prosthetic finger retention: a new approach. Orthotics and Prosthetics 1983 ;37:2:28-30.
16. Pillet (1992) Op cit. 234.