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The Development of a Sheep Amputation Model to Investigate Aspects of Transcutaneous Osseointegrated Exoprosthetic Attachment

James Peter Beck, MD

Body armor and advanced, in theater, resuscitation techniques are saving a higher percentage of combat casualty victims on the battlefields of Iraq and Afghanistan, than in any previous U.S. military conflicts. The cost of a life saved, however, is often a soldier living with the results of severe multiple extremity bone and soft tissue trauma, salvaged only by multiple limb amputations. The resulting “short stump” amputees cannot be fitted with conventional socket attachment technology because the remaining limb is too short to hold the external prosthesis and they are thus consigned to life in a wheelchair or without hand function. Direct attachment of the artificial limb to the remaining short stump bone, via a Titanium implant passing through the skin, and anchored into the residual bone, provides an ideal and robust docking system. This alternative to socket technology is a clinically proven concept in Europe, in human volunteers. While these patients have vastly improved function, and can walk and even “feel” objects and the ground through the bone attachment (osseoperception), the clinical problem of superficial and deep catastrophic infection remains unsolved. Skin/implant site hygiene and conventional antibiotic therapy has failed to prevent infection, the latter because of rapidly evolving antibiotic resistant pathogens. Since various antimicrobial strategies, bacterial challenges and analysis of the skin/implant interface and bone/implant attachment cannot be studied in the human model, we have developed a large animal model of transcutaneous osseointegrated prosthetic attachment. We have successfully designed a Titanium bone-ingrowth prosthesis and implanted it into the third metacarpal bone of 85 sheep. By using skin attachment to the prosthesis these animals remain fully ambulatory and without infection, for up to one year. These animals are however “unchallenged” beyond barnyard pathogens. With this model and others we intend to explore various anti-infection strategies including that of therapeutic bacteriophages. The broader extension of this technology would include the prevention of other device related infections such as those of central venous and urinary catheters, chronic endotracheal intubation and left ventricular assist devices.

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