Prostheses for partial hand amputations
L. F. Bender *
Amputation of part of a hand may create significant functional limitations for the amputee which are difficult to ameliorate by either orthoses or prostheses. To help develop a logical approach to devices for partial hand amputations the patterns of losses have been studied and a division into four categories has been proposed.Transphalangeal,thumb spared; thenar, partial or complete; transmetacarpal, distal; transmetacarpal, proximal.
By utilizing basic principles of orthotics and prosthetics and by exercising ingenuity, it is often possible to provide considerable improvement in function and/or cosmesis to individuals with partial hand amputations. Case illustra-tions and their prosthetic solutions are presented.
The author has attempted to provide both function and cosmesis to many persons with partial hand amputations and has been con-fronted by a variety of patterns of amputation and many different vocational and avocational needs. Because of this great variation in patterns of amputation and also to help develop a logical approach to devices for partial hand amputations the losses have been studied and divided into categories.
Traumatic amputation of a part of the hand in an industrial accident usually occurs in a straight line through the phalanges or meta-carpals but may be at any angle with relation-ship to a line through the distal row of carpal bones. The injury may remove, spare, or partially involve the thumb.
Farm accidents, on the other hand, are more often uneven at the amputation site due to the tearipg, clawing or shredding action of farm implements.
The loss classification proposed (Fig. 1 ) divides partial hand amputations into four categories :
Transphalangeal, thumb spared.
Thenar, partial or complete.
Transmetacarpal, distal; thumb spared or involved.
Transmetacarpal, proximal; thumb spared or involved.
Transphalangeal amputations usually involve the four fingers to similar or slightly varying degrees. Most often these patients need no device, but they may desire cosmetic fingers; these can be easily fitted if at least half of the proximal phalanx remains for each finger. Cosmetic fingers may be held on by suction or by special adhesives. Occasionally such a person needs and desires additional function.
A thirty year old male lost his right fingers in an industrial accident involving metal shears. A portion of the proximal phalanx of digits two through five remained with good range of motion and strength at the metacarpophalangeal joints, the thumb was spared. He was right dominant and wanted to continue to use tools with his right hand. However, the proximal phalanx of the fifth digit was considerably shorter than that of the second digit so power grip was not effective. A stainless steel prosthesis with Plastisol covering was designed and fabricated (Fig. 2 ).
The side MCP hinge moves freely and permits the strength of the finger flexor muscles to flex the opposition bar and provide satisfactory grip of handles and tubular objects (Fig. 3 ).
Amputation of the thumb alone is relatively rare in our experience. When it does occur and involves the metacarpal, as well as the phalanges, a prosthetic thumb can be made (Fig. 4 ). Plastic laminates can be shaped to closely resemble a thumb and to provide a shallow socket that fits against the second metacarpal and is held on by a Velcro or Plastisol strap around the hand. If other digits adjacent to the thumb are also amputated, the prosthesis can be made with a wider socket and still provide a satisfactory prehension post.
Amputations through, the distal transmetacarpal area are quite common in the author's industrial location. Since most of these persons have been involved in hard working occupations and probably will continue to do skilled and semi-skilled labour, stout devices must be made for them.
Basically, two alternatives are available to the orthotist or prosthetist in dealing with distal transmetacarpal amputations. A prosthesis shaped like a mitt can be constructed or an open steel prosthesis can be designed to fill a specific need (Fig. 5 ).
The mitt prosthesis must be particularly strong in the distal portion. The palmar area is lined with Neoprene so it will not be too slippery. This prosthesis provides a large prehension area for gross activities such as lifting furniture and also permits finger tip prehension along the rim of the mitt.
Poor skin coverage of the amputation site is an unusual problem. Surgical techniques usually permit satisfactory skin coverage of distal amputation sites.
A sixty year old farmer lost all fingers, including the thumb, at the distal transmetacarpal level in a corn-picker machinery accident (Fig. 6 ). Adequate skin coverage was not achieved because he did not permit additional surgery to cover the stump with skin graft. The amputation site was sensitive and needed protection. He also desired function; needing to grasp mechanical milkers firmly so he could attach them to his cows. A stainless steel prosthesis was designed with a contoured piece of 1 '2mm stainless steel dorsally which wrapped around the fifth metacarpal and stopped at the fourth metacarpal. A small steel rod was positioned in the thumb web space for stability and to prevent proximal movement of the prosthesis. Stainless steel rods, 4.5mm in diameter, were contoured dorsal and slightly distal to the sensitive amputation site to prevent bumping it and to add strength to the unit. A second set of stainless steel rods were then positioned so that they would hold a semicircular opposition post in place. The post is silver soldered to the rods at the appropriate angle to hold tubular objects such as milkers. Proper design and positioning of the post is important. One must consider carefully the length, range of motion, and strength of the thumb as well as the size, shape and weight of the objects to be picked up. Plastisol coating provides a non-absorbent, resilient, pleasing appearance but the Plastisol must be roughened on the prehension surface of the opposition post to provide adequate friction for good function.
The thumb may be spared, partially amputated, or absent in amputations through the proximal transmetacarpal area of the hand. Either cosmetic hands or functional prosthesis or both may be used to restore appearance and function.
A twenty nine year old female lost all right fingers and thumb in a punch press accident (Fig. 7 ). A right dominant person, she desired cosmesis and sufficient function to hold small objects and feeding utensils. Appearance of her hand was restored by a cosmetic plastic glove with semi-rigid fillers in the fingers and a zipper fastening on the volar aspect of the wrist.
An opposition post also was constructed with a short post to oppose the stump of the first metacarpal. It provided the desired function.
An alternative solution in proximal transmeta-carpal amputations with sparing of the thumb is to fabricate an epoxy resin mitt (Fig. 8 ). To gain stability the mitt will usually have to encase the carpal area. It can be made sufficiently flexible yet semi-rigid that it can be slipped over the stump and held in place with a single Velcro strap. The rim of the mitt can be made to any desired shape so that utensils and small objects can be picked up as well as providing sufficient opening to grasp larger objects like an electric razor.
By utilizing basic principles of orthotics and prosthetics and by exercising ingenuity it is often possible to provide considerable improvement in function and/or cosmesis to individuals with partial hand amputations.