Dentistry and orthopaedics
As early as the 1970s, titanium was of key importance in odontology. A typical dental implant involves drilling into the jawbone and inserting a titanium screw with a rough surface. The gum tissue is replaced over the hole so that there is no pressure on the screw for some months to allow osseointegration. Then the tooth itself or a bridge is fastened via a small abutment over the screw. The five-year survival rate of such implants is reported to be more than 95 % (12).
Interest in the orthopaedic use of titanium came somewhat later than in dentistry, but early in the 1980s it became clear that cementless hip prostheses with an alloy of cobalt, chromium and molybdenum (CoCrMo), known in medicine as Vitallium, gave poor bone fixation and weak clinical outcomes (13). These problems led to increased interest in improving cementless prostheses. Greater understanding of the osseointegration of implants resulted in the development of the first cementless titanium hip prosthesis. It was introduced under the name Zweymüller, after the Viennese orthopaedist who started testing it in 1980 (14) (Figure 2). In Norway, titanium femoral prostheses were introduced in 1984 (15). All cementless primary femoral prostheses now inserted in Norway are made of titanium, and the 20-year survival rate of such implants is over 90 % (16).
Titanium's active surface means that the metal is unsuitable as a sliding surface in joints. For the femoral head of the hip joint, an alloy of cobalt, chromium and molybdenum, steel or ceramics is preferred. When long bones are fractured, surgical steel is preferred. However, plates, screws and intramedullary nails of titanium are used for osteosynthesis in smaller bones. In the case of amputees, intramedullary titanium nails that protrude from the skin can be attached to external prostheses in a similar manner to dental implants. This can, for example, provide prosthetic function in patients with short transfemoral or transhumeral amputation stumps, where it is otherwise difficult to attach external prostheses. Patients receiving this type of prosthesis acquire a kind of 'osseoperception' via the osseointegrated intramedullary nail that gives a more accurate sensation of how the prothesis moves and what the underlying ground surface is like. Ulceration and infection in the area between skin and intramedullary nail can occur, but this is a minor complication (17).
As is often the case with innovations in medicine, titanium metal had a long and difficult journey to acceptance