Analysis of UHMWPE wear particles produced in the simulation of hip and knee wear mechanisms with the RandomPOD system

If the wear rate of ultrahigh molecular weight polyethylene (UHMWPE) components of prosthetic joints is high, the microscopic UHMWPE wear particles that are produced in large numbers are known to cause osteolysis. This may lead to the loosening of fixation of the implant. Conventional UHMWPE GUR 1020 wear particles produced with the novel RandomPOD wear test system were analyzed by scanning electron microscopy. Worn UHMWPE surfaces were analyzed as well. The wear tests included the simulation of both hip (flat-on-flat) and knee (ball-on-flat) wear mechanisms against polished CoCr in serum. The same non-cyclic motion and load input were used in both cases. The diameter of the hip wear particles was 0.30 μm ± 0.15 μm. The knee wear particles were on the average five-fold larger, 1.5 μm ± 0.9 μm in diameter. The principal wear mechanism was moderate adhesive wear, which was macroscopically manifested as burnishing. The sizes of the particles and the burnishing were in agreement with clinical findings. The RandomPOD was shown to be the first pin-on-disc wear test device to meet these principal validation criteria regarding simulation of wear mechanisms for both the prosthetic hip and the prosthetic knee.