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Conclusions.Fixed valgus angle resection is not reliable in restoring mechanical axis in total kneearthroplasty. In the absence of facilities for surgical navigation, a pre operative planning withlong leg films is extremely important to achieve long-term success.Friday, October 8, 2010, 15:20-16:00Session B14: Hip ResurfacingHip Implants - Tribological Testing Influenced by Physiological Conditions*Joseph Pamu - Smith & Nephew - Leamington Spa, EnglandAmir Kamali - Smith & Nephew - Leamington Spa, EnglandJasper Daniel - - , United KingdomAzad Hussain - Smith & Nephew Orthopaedics Ltd - Leamington Spa, UKChenxi Li - Smith & Nephew Orthopaedics Ltd - Leamington Spa, England*Email: joseph.pamu@smith-nephew.comIntroduction: Hip implant research has been carried out for decades using hip simulators toreflect situations in vivo. With regards to metal on metal (MoM) implant testing, it has beenreported that there is no significant difference between the wear generated by various cobaltchromium (CoCr) microstructures. On the contrary, higher wear, metal ion levels andsubsequent failures have been reported in heat treated (high carbon, low carbide) devicescompared to as cast (high carbon, high carbide) devices in vivo. During testing, the bearingsurfaces may be masked from the effect of microstructure on wear under fast and continuouscycles, while in vivo, the extensive range of kinetics and kinematics, stop/start motion, varyingwalking frequencies could break down the fluid film, resulting in a less favourable lubricationregime. The aims of this study were to develop a more physiologically relevant hip simulatortest protocol, and investigate the effect of microstructure on wear.Materials & Methods: Three pairs of 50mm as cast (AC) and four pairs of 50mm double heattreated (DHT) CoCr MoM devices were tested in a ProSim hip simulator. In order to determinethe frequency for testing, Patients’ activities have been monitored using a Step Activity Monitor(SAM) device. The data showed a relatively slower walking pace (frequency) than that used inthe hip simulator studies. The new frequency, along with stop/start motion and various kineticsand kinematics profiles have been used in putting together a more physiologically relevant hipsimulator test protocol. The lubricant used in this study was new born calf serum with 0.2 %(w/v) sodium azide concentration diluted with de-ionised water to achieve an average proteinconcentration of 20 g/l. Gravimetric measurements have been taken at 0.5, 1, 1.5 & 2 millioncycle (Mc) stages and ion analysis has been carried out on the serum samples.Results & Discussions: A biphasic wear pattern similar to the parts in vivo was observed.Under the newly developed physiologically relevant test conditions, the DHT CoCr devicesgenerated 40% higher wear than the AC CoCr devices (Figure 1).The metal ion analysis results also showed a similar biphasic wear trend, however, thedifference between the AC and DHT devices was further increased by approximately 30 % at 2file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]