Surgery – Truss – Pad
Patent
1981-11-23
1984-10-16
Padgett, Benjamin R.
Surgery
Truss
Pad
128 92C, A61F 104
Patent
active
044765908
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to endoprosthetic implants for the human or animal body and provides a manner of rendering such implants antimicrobial. The invention has particular, but not exclusive, application to orthopaedic implants.
As used in this Specification (including the claims thereof), the term "endoprosthetic implant" includes the entire implant, parts thereof and fixing means therefor. In particular, said term includes, for example, orthopaedic pins, plates and screws, and artificial joints.
With few exceptions, it has been the established practice for many years to manufacture endoprosthetic implants from materials which induce minimal tissue response and effects and yet possess adequate mechanical properties for the particular application. In the particular case of endoprosthetic orthopaedic implants, structural materials usually have been sought which do not corrode in vivo and which do not cause bone reabsorption.
Materials used for orthopaedic implants have progressed from the early use of common metals and their alloys, especially mild steel, through the use of surgical stainless steel to the present day use of cobalt chromium molybdenum alloys and titanium and titanium alloys. Other materials which are used in endoprosthetic orthopaedic implants include ceramic and carbon-based materials and some synthetic plastics materials such as ultra-high molecular weight polyethylene, some forms of nylon, polymethylmethacrylate and silicone elastomers. None of these materials have fulfilled entirely the aim of bioinertness (i.e. bioinactivity) in all circumstances, but in general the attempt usually has been towards the use of more fully inert materials to prevent as far as possible any interaction in vivo. The search for materials of greater bioinertness for use in surgical implants continues without diminution.
In the early years of implant surgery, silver was employed in the manufacture of endoprosthetic implants. In particular, silver wire, silver plates and silver-plated screws were used in bone repair surgery and tracheotomy tubes were silver plated. However, the use of silver and silver plated implants had generally ceased by about 1935 in the ever continuing search for greater bioinertness for implant materials. In the particular case of orthopaedic implants, silver was and still is, generally considered to be unacceptable as an implant material, because of poor mechanical properties, connective tissue reaction and excessive subperiosteal bone growth (see, for example, Venable et al, Ann. Surg. 105, 917-938, 1937).
Silver was one of the first metals known to man. Silver artifacts have been found in tombs dating to 4,000 B.C. It is believed that in antiquity, silver was deliberately chosen for water receptacles to conserve the quality of drinking water. Silver needles have traditionally been used in acupuncture, which is one of the oldest forms of invasive medical treatment. The antimicrobial properties of silver compounds have been recognized for about 100 years. The first report of silver compounds for pharmaceutical use is that of aqueous silver nitrate for preventing eye infection in new born babies. Since then a range of silver salts, colloids and complexes have been employed to prevent and control infection. Colloidal metallic silver has been used topically for conjunctivitis, urethritis and vaginitis.
The antimicrobial activity of metallic silver has been exploited in filter elements for domestic and industrial use (see Disinfection, Sterilization, and Preservation; Editor S. S. Block, Publishers Lea and Febiger, Philadelphia, 1977). For this purpose, silver has been deposited on porous carbon or used in the form of a wire, gauze or other physical shape. It is believed that the active agent is the silver ion and that impurities must be present in the metal to expedite oxidation and solution.
The body's ability to counter infection in the immediate vicinity of an implant is reduced thereby increasing the risk of a localised infection around the implant. This risk persists beyond the i
REFERENCES:
patent: 2040806 (1936-05-01), Feigl
patent: 3557795 (1971-01-01), Hirsch
patent: 4054139 (1977-10-01), Crossley
patent: 4263681 (1981-04-01), Notton
"Prophylaxis of Indwelling Urethral Catheter . . . ", Akiyami et al., J. of Urology, 4-1978, vol. 121.
"An In-Vivo Study of Bacterial Response to Inert and Reactive Metals . . . ", Gristina et al., J. of Biomed Mater. Res., Wiley, vol. 10, pp. 273-281 (1976).
Scales John T.
Wilkinson Michael J.
National Research Development Corporation
Padgett Benjamin R.
Wallen T. J.
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