Abstract
Total hip replacement (THR) is one of the most succ essful orthopedic surgical procedures for replacing a broken hip joint. In THR, wear may occur at the articulating s urface of the acetabular cup and the femoral head. In Indonesia, the country with the largest Muslim population in the w orld, most of the inhabitants do salat (praying) ev ery day. THR users are banned from doing salat for fear it will damage the hip joint prostheses. The previous wear calculation methods on the hip joint prostheses use the gravime tric, coordinate measuring machine (CMM), profiler, and geometric method. The disadvantages of the previous methods are that the geometry of the wear patch and the wear volume are only known at the end of the experiment, so they ca nnot be used to calculate the specific wear rate va lues in real time. So far, in every modeling of the hip joint prosthes es, the values of the specific wear rate are assume d to be constant. This paper reports on the design modification of a pin-on-ring tribometer that is used to measure the wear volumes in hip joint prostheses. The result shows that modific ations of the femoral head holder, reciprocating mo tion, elastic joint, and extra displacement transducer is needed to get the specific wear rate value. The calculation metho d to find the delta volume that is the value of displacement less than the displacement minimum ( δmin ) is based on a graph, while the calculation method to find the delta volume that is the value of displacement that is more than the di splacement minimum (δmin ) is based on an equation. In the salat test protocol , the longest test time was during the sujud (prostration) motion, which took 1034.17 minutes in the experiment.
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