A 24-month evaluation of a percutaneous osseointegrated limb-skin interface in an ovine amputation model

Percutaneous osseointegrated (OI) prostheses directly connect an artificial limb to the residual appendicular skeleton via a permanently implanted endoprosthesis with a bridging connector that protrudes through the skin. The resulting stoma produces unique medical and biological challenges. Previously, a study using a large animal amputation model indicated that infection could be largely prevented, for at least a 12-month period, but the terminal epithelium continued to downgrow. The current study was undertaken to test the longer-term efficacy of this implant construct to maintain a stable skin-implant interface for 24 months. Using the previously successful amputation and implantation surgical procedure, a total of eight sheep were fitted with a percutaneous OI prosthesis. Two animals were removed from the study due to early complications. Of the remaining six sheep, one (16.7%) became infected at 15-months post-implantation and five remained infection-free for the intended 24 months. The histological data of the remaining animals further confirmed the grossly observable epithelial downgrowth. Albeit a receding interface, it was clear that all animals that survived to the end of the study had residual fibrous soft-tissue ingrowth into, and debris within, the exposed titanium porous-coated surface. Overall, the data demonstrated that the porous coated subdermal barrier offered initial protection against infection. However, the fibrous skin attachment was continuously lysed over time by the down-growing epithelium.