Polyethylene Hip Resurfacing for Women by Dr. Pritchett

6up to 46 mm. Some, but not all, studies have shownincreased wear with femoral head diameters greaterthan 32 mm. There is substantial and favorableexperience with femoral head diameters of 36 and40 mm. 11,13,27 There is favorable wear simulatordata from polyethylene diameters of 44 and 46mm but no long-term clinical data are available. 11Limiting oxidation has been an additional concernand polyethylene containing Vitamin E is nowavailable. 4Early polyethylene prostheses were secured to thepelvis with polymethylmethacrylate during hip replacementor resurfacing procedures. 1,6,10,30,32 Thiswas very successful but late loosening is commonand, therefore, the use of porous-coated metalbacking had become a very popular and successfulalternative. Because cross-linked polyethylene canfracture, its thickness and the thickness of the metalbacking are subject to engineering limitations.Most engineers recommend using a polyethylenethickness of 3.8 mm or greater and a compositethickness including the metal backing of 10 mm ormore if a two-piece component is selected.Cobalt-chromium alloys are used widely as bearingsurfaces against polyethylene for hip and kneeimplants. Cobalt-chromium is harder and moreresistant to corrosion than previous metals usedin joint replacement, such as stainless steel. Titaniumis much too soft to use as a bearing surface.Cobalt-chromium surfaces can be damaged andexhibit low wetability. Newer cobalt-chromiumsurfaces are superior to older implants with respectto smoothness. Ceramic materials generally offerharder and more hydrophilic surfaces compared tocobalt chromium and can be polished to a very lowdegree of roughness. 14Alumina-based ceramics have very favorable wearcharacteristics but there have been rare reports ofimplant fracture. 29 Reports of yttria-stabilized zirconiashowed no reduction in wear when used withcross-linked polyethylene. 25 Oxidized zirconia hasfavorable wear results in hip simulator studies buthas not been manufactured for use in resurfacing. 3Magnesia-stabilized zirconia was chosen for use inour patients because of its superior wear characteristicsin a hip simulator. 25 Also, there was no difficultyin preparing thin-walled stemmed prosthesesappropriate for resurfacing applications. 21,27There are no long-term data available for usingcross-linked polyethylene for resurfacing applicationseither with cobalt-chromium or ceramic prostheses.A nitrated (ceramized) resurfacing prosthesishas been used on a limited basis articulatingwith non-cross-linked polyethylene. The durabilityhas been up to 11 years. 15Polyethylene should be reconsidered for resurfacingbecause of the superior wear characteristics ofcross-linked polyethylene. Also, newer cobaltchromiumprostheses have reduced roughness. Itwill take many years to confirm the wisdom of thisapproach. When polyethylene wear occurs, it isanticipated that revision to another polyethylenebearing without disturbing the well-fixed metalshell will be possible. Women need not be deniedhip resurfacing surgery.