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articulating sphere maintains the standard BHR clearance. The aim of this study was toevaluate the wear performance of the novel DefCom hip joint using a hip wear simulator.Materials and MethodsFive pairs of 50 mm DefCom devices were tested in a ProSim hip wear Simulator for 5 millioncycles (MC) at a frequency of 1 Hz. The lubricant was new born calf serum with 0.2% sodiumazide diluted with de-ionised water to achieve protein concentration of 20 mg/ml. Theflexion/extension was 30° and 15° and the internal/external rotation was 10°. The force wasPaul-type stance phase loading with a maximum load of 3 kN and a standard ISO swing phaseload of 0.3 kN. Five standard 50 mm BHR devices were tested under the same testingconditions for comparison. Statistical analyses were performed at a 95% confidence level (CL)using the statistics function in Excel (Microsoft® Excel 2003).ResultsFig. 1 shows the cumulative volume loss against number of wear cycles for the DefCom and theBHR devices. Similar to the BHR device, the DefCom joints experienced relatively higheramount of material loss during the running-in phase from 0 to 1.0 Mc. However, the running-inwear rate for the DefCom device (0.23 ± 0.06 mm 3 /MC) was much lower than that for the BHRdevice (0.72 ± 0.15 mm 3 /MC). Steady state wear was achieved for all the joints from 1.0 to 5.0MC. The steady state wear rate was 0.11 ± 0.03 mm 3 /MC for DefCom and 0.18 ± 0.01mm 3 /MC for the BHR joints.DiscussionThis study has shown that the DefCom acetabular cup has the potential to reduce the initialrunning-in wear by reducing the clearance at the contact area between the head and cup. Thedevice also has the potential to avoid deformation induced head seizure and high frictionaltorque by maintaining a larger clearance at the periphery of the cup.REFERENCE:[1] D. Dowson, Proc IMeche Part H: J. Eng Med, Vol. 220 H2, pp 161.[2] Kamali, et al, Transactions Vol.34, Las Vegas, NV, 2009, poster 2219,[3] Morlock et al, Med Eng & Phys 31, 2009, pp160-164.Fig. 1. Total volume loss of DefCom and BHR devices (Error bar represents ± 95% ConfidenceLimit)Figuresfile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]