Cobalt prosthesis

Immunologic An aseptic lymphocyte-domi-nated-vasculitis-associated lesion (ALVAL) was reported in a patient in whom cobalt sensitization developed after insertion of a chromium-cobalt prosthesis [22" ]. 

The materials used in a total joint replacement ate designed to enable the joint to function normally. The artificial components ate generally composed of a metal piece that fits closely into bone tissue. The metals ate varied and include stainless steel or alloys of cobalt, chrome, and titanium. The plastic material used in implants is a polyethylene that is extremely durable and wear-resistant. Also, a bone cement, a methacrylate, is often used to anchor the artificial joint materials into the bone. Cementiess joint replacements have mote tecentiy been developed. In these replacements, the prosthesis and the bone ate made to fit together without the need for bone cement. The implants ate press-fit into the bone. 

Titanium alloys generally show a combination of strength and biocompatibility which makes them suitable for medical devices (prosthesis, surgical instruments). The high strength Ti-6Al-7Nb alloy has several orthodontic applications. Only a limited number of alloys have the necessary combinations of properties needed for successful use in the human body. Titanium and its alloys, stainless steels and cobalt-chromium alloys are the workhorse alloys in the medical device industry. 

The Agility Total Ankle Prosthesis (DePuy) is a semi-constrained, fixed-bearing prosthesis that was designed in 1984 and currently has 510(k) clearance from the FDA [14] (Figure 11.11). In the United States, it is the most commonly used TAR prosthesis and has more than 20 years of clinical experience [55]. The device is currently offered in six sizes of matching tibial and talar components [56]. The device consists of a titanium alloy tibial component, a size-matched and separate UHMWPE insert that slides and locks into the tibial component, and an onlay cobalt-chromium talar component [55, 57, 58]. The tibial articular surface is rotated 20 degrees externally to mimic physiologic ankle anatomy [14, 55]. The semi-constrained... 

---