Development of a soft tissue seal around bone-anchored transcutaneous amputation prostheses

Conventional amputation prosthetics are problematic because they rely on the stump-socket interface for attachment. Intraosseous transcutaneous amputation prostheses (ITAP) could solve these problems; however they rely on the integrity of the soft tissue-implant interface as a barrier to exogenous agents, and in the prevention of downgrowth and marsupilisation. We have used an in vivo animal model to study the soft tissue interfaces around bone-anchored transcutaneous implants. We hypothesise that by facilitating and increasing the area of dermal attachment to the implant epithelial down-growth will be reduced. A flange with a series of 24, 0.7 mm holes positioned immediately below the epithelium was used to increase dermal attachment. This significantly reduced downgrowth and optimised the integrity of the collagenous tissue-implant interface at the dermal level. We postulate that the flange reduces relative interfacial movement at the epithelium-implant interface by providing increased surface area for dermal tissue attachment. A tight seal at the dermal tissue level reduces the degree of downgrowth around ITAP, eliminating marsupilisation as a potential failure modality. Surface topography and coatings did not affect the degree of downgrowth or dermal attachment to straight or flanged implants. A significant negative correlation was observed between downgrowth and both epithelial and dermal attachment. This study shows that a soft tissue-implant interface capable of preventing downgrowth and marsupilisation can develop around a bone-anchored transcutaneous implant, given the incorporation of a porous flange positioned in the dermal tissues immediately below the epithelium. This will benefit applications where bone-anchored transcutaneous implants are used.