Knee joint prostheses are commonly employed for therapy in over-use disorder, and as a result of traffic accident and sports injuries. However, errors that can occur due to their use need to be defined. In order to determine the types and rates of wear that might occur in prosthetic components, wear tests were performed in knee joint simulators that mimiced knee joint motion. In this study, the wear was specifically examined in ultra high molecular weight polyethylene (UHMWPE) insert material in the four-axis knee joint prosthesis wear test simulator, and the causes for it were examined. Wear tests were performed for 3 different cycles, 1 x 10(6), 2 x 10(6) and 3 x 10(6). Following wear tests, microscopic images, and mass loss and surface roughness measurements were taken from the UHMWPE insert condyle surface. With an increase in the number of cycles, pitting wear, scratches, agglomerated particles and delamination were seen more clearly on the UHMWPE material surface, due to repetitive forces on different axes. In addition, surface roughness measurements taken from worn surfaces increased the with the number of cycles, and flexion/extension (F/E) motion range increased with surface roughness. Wear rates in the medial region of the UHMWPE insert were higher than in the lateral region. (C) 2019 The Authors. Published by Elsevier B.V.