Finger Prosthesis

Silicones were also used for the preparation of finger prosthesis, in the case of loss of fingers because of trauma, congenital disorders and excision for neoplastic disorders. Although microsurgical reconstruction by reimplantation or transplantation can be attempted to restore function of many finger defects, it may not be possible in crush and severe injuries. Customized silicone prostheses have a wider rate of acceptance, owing to their comfort, durability and stain resistance, which are far superior to any other available extraoral maxillofacial materials [17]. 

Siloxane-containing devices have also been used as contact lenses, tracheostomy vents, tracheal stents, antireflux cuffs, extracorporeal dialysis, ureteral stents, tibial cups, synovial fluids, toe joints, testes penile prosthesis, gluteal pads, hip implants, pacemakers, intra-aortic balloon pumps, heart valves, eustachian tubes, wrist joints, ear frames, finger joints, and in the construction of brain membranes. Almost all the siloxane polymers are based on various polydimethylsiloxanes. 

The application of polymeric materials in medicine is a fairly specialized area with a wide range of specific applications and requirements. Although the total volume of polymers used in this application may be small compared to the annual production of polyethylene, for example, the total amount of money spent annually on prosthetic and biomedical devices exceeds 16 billion in the United States alone. These applications include over a million dentures, nearly a half billion dental fillings, about six million contact lenses, over a million replacement joints (hip, knee, finger, etc.), about a half million plastic surgery operations (breast prosthesis, facial reconstruction, etc.), over 25,000 heart valves, and 60,000 pacemaker implantations. In addition, over AO,000 patients are on hemodialysis units (artificial kidney) on a regular basis, and over 90,000 coronary bypass operations (often using synthetic polymers) are performed each year (]J. 

Numerous elastomers were evaluated for finger joint prosthesis application. Hexsyn showed the best characteristics for this application. 

Blomerlc finger joint prosthesis for the past four years. 

Finger joint replacements are divided into three types (1) hinge, (2) polycentric, and (c) space-fiUer. The most widely used are the space-filler type. These are made of high performance silicone rubber (polydimethylsiloxane) and are stabilized with a passive fixation method. This method depends on the development of a thin, fibrous membrane between implant and bone, which allows pistoning of the prosthesis. This fixation can provide only minimal rigidity of the joint [Swanson, 1973). Implant wear and cold flow associated with erosive cystic changes of adjacent bone have been reported with silicone implants [Carteret al., 1986 MaistrelU, 1994]. 

FIGURE 32.18 Schematic of the prehension patterns of the hand as defined by Keller, Taylor, and Zahn (1947) (al) palmar prehension (three-jaw chuck), (o2) palmar prehension (two finger), (b) tip prehension, (c) lateral prehension, (<0 hook prehension, (e) spherical prehension, (/) cylindrical prehension. In a handlike prosthesis, it takes two to four independently controlled degrees of freedom to implement these prehension patterns. In a non-hand-like device, a single-degiee-of-free-dom device such as a split hook can be used. 

Kenworthy s hand had the fingers fixed with only the thumb being able to move. While flat-surface operation is important, it is perhaps not the most important feature of prosthesis design. This hand was designed primarily for use in bilateral arm systems in which one hand was a conventional pincer-type hand and the oAer was of Kenworthy s design. The 90 degrees of the Kenworthy hand was chosen so that at least one hand of the bilateral arm system could have flat-surface operation. 

Cool, J. C., and Van Hooieweder, G. J. O. (1971). Hand prosthesis with adaptive internally powered fingers. Medical and Biological Engineering, vol. 9, pp. 33-36. 

Romaquera C, Grimalt F, Vilaplana J (1985) Methyl methacrylate prosthesis dermatitis. Contact Dermatitis 12 172 Shelley ED, Shelley WB (1984) Chronic dermatitis simulating small-plaque parapsoriasis due to cyanoacrylate adhesive used on finger nails. JAMA 252 2455 Tomb RR, Lepoittevin J-P, Durepaire F, et al. (1993) Ectopic contact dermatitis from ethyl-cyanoacrylate instant adhesives. Contact Dermatitis 28 206... 

Elbow joint prosthesis Intervertebral disk Finger joint prosthesis... 

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