Convened under the auspicious of esteemed endorsers - ISTA

Thursday, October 7, 2010, 8:00-8:50Session A1: Alternate Bearings in THA 1Wear Testing of Highly Crosslinked UHMWPE Against 36 Mm CoCr and44 Mm Oxidized Zirconium Femoral HeadsIntroduction:*Amit Parikh - Smith & Nephew, Inc. - Memphis, USAPatrick Hill - Smith & Nephew, Inc. - Memphis, USAVivek Pawar - Smith & Nephew, Inc. - Memphis, USAMark Morrison - Smith & Nephew Orthopaedics - Memphis, USA*Email: amit.parikh@smithnephew.comLarge diameter femoral heads offer increased range of motion and reduced risk ofdislocation. However, their use in total hip arthroplasty has historically been limited by theircorrelation with increased polyethylene wear. The improved wear resistance of highlycrosslinked UHWMPE has led a number of clinicians to transition from implanting traditionallypopular sizes (28mm and 32 mm) to implanting 36 mm heads. Desire to further increasestability and range of motion has spurred interest in even larger sizes (> 36 mm). While thelong-term clinical ramifications are unknown, in-vivo measurements of highly crosslinkedUHMWPE liners indicate increases in head diameter are associated with increased volumetricwear [1]. The goal of this study was to determine if this increase in wear could be negated byusing femoral heads with a ceramic surface, such as oxidized Zr-2.5Nb (OxZr), rather thanCoCrMo (CoCr). Specifically, wear of 10 Mrad crosslinked UHMWPE (XLPE) against 36 mmCoCr and 44 mm OxZr heads was compared.Materials and Methods:Ram-extruded GUR 1050 UHMWPE was crosslinked by gamma irradiation to 10 Mrad,remelted, and machined into acetabular liners. Liners were sterilized using vaporized hydrogenperoxide and tested against either 36 mm CoCr or 44 mm OxZr (OXINIUM) heads (n=3).All implants were manufactured by Smith & Nephew (Memphis, TN).Testing was conducted on a hip simulator (AMTI, Watertown, MA) as previously described[2]. The 4000N peak load (4 time body weight for a 102 kg/ 225 lb patient) and 1.15 Hzfrequency used are based upon data obtained from an instrumented implant during fastwalking/jogging and have previously been shown to generate measurable XLPE wear [2,3].Lubricant was a serum (Alpha Calf Fraction, HyClone Laboratories, Logan, UT) solution thatwas replaced once per week [2]. Liners were weighed at least once every million cycles(Mcycle) over the duration of testing (~ 5 Mcycle). Loaded soak controls were used to correctfor fluid absorption. Single factor ANOVA was used to compare groups (α = 0.05).Results:The predominant wear feature displayed on the articular surface of liners was burnishing.There were no signs of fatigue wear or of delamination. Mean wear rates (± std dev) of linersarticulated against 36mm CoCr and 44 mm OxZr heads were 3.7 ± 0.4 mm 3 /Mcycle and 2.7 ±0.4 mm 3 /Mcycle, respectively (Figure 1). This difference was statistically significant (p =file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]