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Compared to a cruciate retaining knee prosthesis, an anterior stabilized prosthesis has what effect on the contact area and what effect on the stability in PCL deficient knees?
Decreased contact area; increased stability
Increased contact area; increased stability
No change in contact area; no change in stability
Decreased contact area; decreased stability
Increased contact area; decreased stability
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How are free radicals removed from highly cross-linked polyethylene?
What polyethylene processing step results in increased polyethylene wear and subsequent osteolysis?
Gamma irradiation in air
Remelting after gamma irradiation in nitrogen
Ethylene oxide sterilization
Which of the following manufacturing techniques of UHMWPE results in the lowest susceptibility to fatigue crack formation and propagation in joint arthroplasty bearings?
Ram bar extrusion with secondary machining into the desired product
Hot isostatic pressing into bars with secondary machining
Irradiation with 10 Mrad of radiation achieiving a polyethylene crystallinity of >99%
Direct compression molding from PE powder to the desired product
Addition of calcium stearate to the polyethylene resin followed by compression molding into bars with secondary machining into the desired product
Polyethylene gamma irradiation in nitrogen gas results in which of the following?
When comparing unaged, radiated, cross-linked, ultra-high molecular weight polyethylenes (XPE) treated with remelting or annealing, annealed XPE has
fewer free radicals, better mechanical characteristics, and lower wear than remelted XPE.
fewer free radicals, worse mechanical characteristics, and lower wear than remelted XPE.
more free radicals, better mechanical characteristics, and equivalent wear than remelted XPE.
more free radicals, worse mechanical characteristics, and equivalent wear than remelted XPE.
equivalent free radicals, better mechanical characteristics, and lower wear than remelted XPE.
When polyethylene is exposed to radiation and subsequently heated, certain chemical changes occur in the material. Which of the following statements best describes these changes?
The process converts an otherwise interpenetrating networking structure of polymer chains into a linear, high molecular weight polyethylene macromolecule.
The process increases the ductility of the material.
The process leads to fewer particles that are larger in size than the untreated material.
The process improves (lowers) the wear rate but may increase the risk of fracture.
The process decreases the wear rate of the material, compared to untreated polyethylene, when tested against a rough counterface.
Sterilization of ultra-high molecular weight polyethylene by gamma irradiation in air will degrade its wear performance because of
A 55-year-old male undergoes a revision total knee arthroplasty of an implant that is only 3 years old. At the time of surgery, the tibial polyethylene liner shows catastrophic delamination and cracking. What is the most likely cause of this extensive, accelerated wear of the polyethylene liner?
Sterilization in ethylene oxide
Gamma irradiation of the polyethylene liner in the presence of air
Gamma irradiation of the polyethylene liner with vacuum packaging
Gamma irradiation of the polyethylene liner in nitrogen
Gamma irradiation of the polyethylene liner in argon
In evaluating methods of polyetheylene sterilization for hip arthroplasty, gamma-irradiation in air compared to irradiation in an inert substance results in which of the following?
No difference in regards to outcome
Higher rate of cross-linking when irradiated in air
Lower rate of oxidation when irradiated in air
Accelerated wear and failure when irradiated in air
Better wear resistance and longevity when irradiated in air