Page 50 - Demo

Chapter 248Current materialsCobalt-chromium alloyAfter first being introduced in orthopedic surgery, CoCr found its way to TMJ surgery in 1951, when Kleitsch and Castigliano used a Vitallium plate to prevent recurring ankylosis.(11,91) As it became clear that the material possessed several highly interesting properties such as high strength and fatigue resistance, high corrosion resistance, and good biocompatibility, it quickly became a favored implantation material. Due to its excellent wear resistance, it was even used as an articulating surface in total hip arthroplasty.(51) Although several systems made use of CoCr, such as the Biomet Lorenz and TMJ Concepts device, the system that most heavily relied on the use of a CoCr alloy was the metal-on-metal Christensen TJR system. While other systems articulated using metalon-polyethylene communication, Christensen based his system on the early theoretical success of the metal-on-metal hip prosthesis and used a metal-on-metal articulation. This decision was based on the fact that the total wear volume in a metal-on-metal hip prosthesis is around a tenfold to even 100 times less than compared to a metal-on-UHMWPE implant.(46,52) What Christensen failed to notice, however, was that while the hip is a constrained joint, this is not the case for the TMJ, which is much more like the knee.(91) As a result, cyclic loading of the fossa could lead to micromotion, fretting corrosion, fatigue, and even fracturing of the fossa.(92) Also, although metal-on-metal TMJ devices produced less wear volume, the incidence of metal hypersensitivity was higher than with metal-on-UHMWPE prostheses, as was concluded by Wolford and Cassano after following up on 115 patients with a Christensen or TMJ Concepts system.(93) While only 3% of TMJ Concepts prostheses had to be removed due to metal hypersensitivity or device failure, 33% of Christensen prostheses had to be explanted. Similar findings were made by Sidebottom et al.,(94) who abandoned the Christensen system altogether.Wolford et al.(53) reported that patients fitted with a metal-on-metal device exhibited significantly elevated body levels of Co and Cr. In comparison, patients fitted with a TMJ Concepts prosthesis showed no signs of UHMWPE or metallic debris, which indicated good wear Nikolas de Meurechy NW.indd 48 05-06-2024 10:14