An antimicrobial containment cap is provided for use in a bone anchored prosthesis mounting system of the type having an externally protruding fixator pin carried by all implanted bone anchored mounting post, wherein the fixator pin accommodates removable attachment to an exoskeletal prosthesis such as a prosthetic limb or the like for an amputee. The containment cap, when mounted onto the fixator pin, is interposed between the prosthesis and soft tissue covering the end or stump of an amputated residual limb or the like. The containment cap carries and supports a selected antimicrobial or antibacterial agent in substantial contact with the soft stump tissue in a position closely overlying and substantially circumscribing the tissue interface with the externally protruding fixator pin to safeguard against infection. The containment cap is adapted for quick and easy periodic removal for cleaning and/or replenishment of the antimicrobial agent.