Abstract
Introduction: Normal limb use in amputees with made to measure external prostheses can be impaired by problems at the stump – socket interface. The development of an Intraosseous Transcutaneous Amputation Prosthesis (ITAP) would overcome the problems by protecting the soft tissues, whilst redistributing high stresses to bone. ITAP creates a breach in the skins protective barrier to infection, hence requires a sufficient soft tissue – implant seal to prevent implant failure. Deer antlers are natural analogues of ITAP, and successfully overcome the problems associated with skin penetrating implants such as infection, marsupilisation and avulsion. In this study, an ITAP device has been developed, with a successful soft tissue – implant interface, based on deer antler morphology. It is hypothesised that sub-epithelial dermal fibroblastic, but not epithelial layer adhesion, is directly responsible for the degree of downgrowth observed around ITAP.
Methods: Eleven pairs of deer antler were used to histologically evaluate the interface between the antler and pedicle, and the soft tissue seal around the antler-pedicle structure. The findings were used to develop a titanium alloy (Ti6Al4V) ITAP device in a goat model. Three to five transcutaneous pins were implanted into the medial aspect of the right tibia of skeletally mature female goats. Four implant designs were tested, Machine Finished Straight (MFS), Hydroxyapatite (HA) Coated MFS, Machine Finished Flanged (MFF) and HA Coated MFF. The 70μ thick HA coating was applied to the implant region abutting the sub-epithelium. The implants remained in situ for four weeks after which the histology of the resulting interfaces were analysed qualitatively and quantitatively for degrees of epithelial downgrowth (marsupilisation) and epithelial/sub-epithelial layer attachment to the implant surface.
Results: The histology of the deer antler showed there to be an extremely small area of epithelial attachment, with negligible downgrowth, arrested by soft tissue adhesion to the underlying pedicle surface. There was a significant increase in pore size and frequency in the pedicle structure (abutting the soft tissues), compared to the antler proper. The MFS ITAP implants were associated with significantly greater downgrowth and reduced epithelial and sub-epithelial layer attachment compared to all other implant designs. The HA coating, and porous flange structure significantly reduced downgrowth and increased sub-epithelial layer attachment. Regression correlation showed that there is a significant negative correlation between the extent of downgrowth and the degree of sub-epithelial dermal fibroblastic layer attachment observed around ITAP implants (All p values < 0.05).
Discussion: Deer antlers successfully overcome the potential problems for ITAP. By artificially recreating some of the aspects of the antler, including layering of porous and bioactive surfaces for tissue adhesion, we have successfully developed an ITAP implant that minimises downgrowth and actively encourages epithelial and sub-epithelial soft tissue adhesion.
Correspondence should be addressed to Mr Carlos Wigderowitz, Honorary Secretary BORS, University Dept of Orthopaedic & Trauma Surgery, Ninewells Hospital & Medical School, Dundee DD1 9SY.
