Metallic femoral components

In the present study, a knee joint simulator is used to simulate the tibial axis load and flexion-extension motion under walking condition. The lubrication condition or fluid film formation in knee prosthesis models is evaluated by measuring the electric contact resistance between the femoral metallic component and tibial conductive polymeric or elastomeric component under the constant applied voltage in a knee joint simulator. 

Dowson, D. (1995) A comparative study of the performance of metallic and ceramic femoral head components in total replacement hip joints. Wear, 190, 171-183. 

Fig. 5.2 Example total knee replacement system. The top portion of the figure highlights the polyethylene components available for the Persona personalized knee system manufactured by Zimmer, which includes both the tibia trays and the patellar resurfacing components. These liners are made from highly-crosslinked polyethylene with vitamin E added. In the bottom portion of the figure tibial trays are shown in their articulating position between the femoral and tibial metal components...

In 1938, Wiles was reported to have performed the first hip arthroplasty, consisting of stainless-steel femoral and metal components that were fixed to the bone without cement [29]. Although many clinical records of Wiles patients were lost in World War II, some radiographs of Wiles prosthesis can stiU be found at the Chamley museum in Wrightington (Wigan, England), as shown in Figure 6.4. 

The next advance in total hip arthroplasty came with the development of various porous surface treatments which allow bone tissue to grow into the metal porous coating on the femoral stem of the hip implant and on the acetabular component of the total joint replacement. These developments arose because of patients who were not able to tolerate cemented implants because of allergies to the cement, methylmethacrylate. More youthflil patients are better served by a press-fit implant as well. Figure 12 shows the difference between textured and beaded surface-treated orthopedic prostheses. 

The head of the femoral component then articulates with an ion-bombarded, HDPE, high walled, acetabular liner which fits iato a screwed ia, machined, titanium, chromium—cobalt—molybdenum or vanadium—aluminum metallic alloy hydroxyapatite-coated acetabular shell/cup. Each of the separate parts of the modular system for total hip arthroplasty is manufactured ia several different sizes. 

Another widely used surgical procedure is knee replacement. In this operation the natural components of the knee joint are replaced with an artificial femoral component made of metal that interfaces with a tibial plateau made of ultra-high molar mass poly(ethylene). Implantation of these joints is becoming more widespread, though the demand for them is not as great as for hip replacement. 

Penetration of Metallic Femoral Components into Polymeric Tibial Components Observed in a Knee Joint Simulator... 

A knee joint simulator designed to evaluate the mechanical and tribological characteristics of total replacement knee joints will be described. Measurements of penetrations of metallic femoral components into the polymeric tibial components by means of dual index holographic contouring will be presented and the findings compared with observations from detailed studies of wear in well-controlled laboratory machines and the limited evidence of in-vivo performance of replacement knee joints. 

A knee joint simulator was designed and built in the bioengineering laboratory at Leeds in the late 1970 s to enable the mechanical and tribological characteristics of current and projected knee joint replacements tp.he assessed. The simulator has been described by Dowson et al and it is shown in Figure 1. Realistic load and motion cycles are applied to the knee joints to simulate any desired activity, but usually walking, and the penetration of the metallic femoral components into the polymeric tibial components after a large number of cycles can then be used to assess the life of the joints. Furthermore, the penetrations recorded, which include both wear and creep, can be related to results of laboratory wear studies of the behaviour of UHMWPE and to the in-vivo performance of total replacement knee joints. The simulator is therefore an Important machine in both the pragmatic and fundamental aspects of total replacement knee join development. 

As noted in Section 12.5.1, a family of polyaxial copolyesters described in Chapter 2 can be used to prepare two or more of the critical components of a femoral sealing device. Other compliant members of this family of polymers, which can be converted to compliant, stretchable membranes and strong, stretchable monofilament fibers, can be used to construct a mantle or cover for metallic endovascular stents. Thus, a composite of thin film, reinforced with a monofilament in cross-coiled configuration, can be assembled into a highly compliant, expandable, tubular mantle or sleeve. This can be placed tightly as a cover outside an expandable metallic or polymeric stent so that under concentric irreversible expansion at the desired site of... 

Gunston and MacKenzie s response to severe patello-femoral pain was to develop a separate patello-femoral arthroplasty, which consisted of a metallic patellar button articulating against an UHMWPE track implanted in the femur (1976). Because this solution required the implantation of two additional components, they cautioned against using this solution for patello-femoral replacement "indiscriminately" (1976). 

J. Karrholm, W. Freeh, K.-G. Nilsson and F. Snorrason, Increased metal release from cemented femoral components made of titanium alloy, Acta Orthop. Scand., 65, 599-604 (1994). 

It is likely that cordierite, titanate and zirconate ceramics will record the most rapid rates of growth, due to their uses in environmental systems, medical products, electronic components, and household appUances. A continued expansion in electronic component shipments will provide opportunities for titanate per-ovskites and other ceramics. Nonetheless, cordierite, titanates and other ceramics will undoubtedly benefit from a continued, environmentally driven trend to reduce the amounts of particulates, nitrogen oxides (NO,), and sulfur oxides that are released into the atmosphere. Technological advances in the medical product market will also provide many opportunities, notably for monohthic ceramics such as alumina and zirconia used for femoral balls in hip endoprostheses, as well as biocompatible hydroxyapatite and tricalcium phosphate coatings for the metal stems of hip implants (see also Chapter 10). Likewise, dental ceramics wiU continue to experience high growth rates through 2010. 

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