Knee replacement, UHMWPE

Carbon fibers have been incorporated in the high density polyethylene used in total knee replacements (Figure 41.5). The standard ultra high molecular weight polyethylene (UHMWPE) used in these implants... 

Total knee replacements can be implanted with or without cement, the latter relying on porous coating for fixation. The femoral components are typically made of CoCr alloy and the monolithic tibial components are made of UHMWPE. In modular components, the tibial polyethylene component assembles onto a titanium alloy tibial tray. The patellar component is made of UHMWPE, and a titanium ahoy back is added to components designed for uncemented use. The relatively small size of the pateUar component compared to the forces that travel through the extensor mechanism, and the small area of bone available for anchorage of the prosthesis, make the pateUa vulnerable. 

Chapter 7 The Origins and Adaptations of UHMWPE for Knee Replacements... 

Chapter 8 The Clinical Performance of UHMWPE in Knee Replacements... 

Although knee arthroplasty enjoys a remarkable clinical track record, problems with wear and fatigue damage of UHMWPE continue to limit the longevity of both unicondylar and bicondylar knee replacement components. Unlike in the hip, where radiographic techniques have been developed to quantify in vivo wear rates, there currently exist no standard and widely accepted techniques for tracking the clinical performance of UHMWPE in patients with knee replacement. Thus, today the most effective way to evaluate the in vivo performance of UHMWPE continues to be the analysis of retrieved components from revision surgery or from autopsy donations. 

Stresses in UHMWPE Tibial and Patellar Components for Total Knee Replacement... 

Failure of an IB I knee replacement after 14 years in vivo due to wear of the UHMWPE component. (A) Standing A-P radiograph shows narrowing of the joint space in the medial compartment (indicated by arrows). (B) The retrieved UHMWPE component was worn completely through on the medial side. The tibial tray was polished (i.e., burnished) from articulation with the femoral component. Severe metallosis of the surrounding tissues was... 

Despite its successful track record, wear and damage of the UHMWPE insert compromises the longevity of knee arthroplasty. Osteolysis, a rare occurrence with all-UHMWPE tibial components, has been documented with increasing frequency in modular knee replacements. Clearly, improved wear behavior of the UHMWPE insert would be advantageous from the perspective of reducing the risk of osteolysis and aseptic loosening. 

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