Failure analysis of retrieved UHMWPE tibial insert in total knee replacement

This study involves the failure analysis of an ultra high molecular polyethylene (UHMWPE) tibial insert from Apollo® Total Knee System, which was removed after 10 years of service from 70 years old female patient. The tibial insert was investigated by using a stereoscope, scanning electron microscope (SEM), infinite focus microscope (IFM) and energy disperse spectroscopy (EDS) to characterize the morphology and composition of the bearing surface. Differential scanning calorimetry (DSC) and Fourier transform spectroscopy (FTIR) were employed to characterize the degradation and crystallinity of the component. Gel-permeation chromatography (GPC) was used to measure the polyethylene tibial insert molecular weight. Results showed that the failure of total knee replacement (TKR) was associated with high grade wear and oxidation degradation. Surface delamination, scratch marks, pitting, folding, and embedded third body particles were observed on the retrieved UHMWPE tibial surface. Pit depth as large as 60 μm was measured on the surface. The damage features observed on the UHMWPE tibial insert suggested degradation is due to fatigue related wear and is oxidation-induced. Overall results show that the UHMWPE tibial insert which was retrieved from a patient who is active and but not overweight underwent degradation of material properties and high grade wear during 10 years of service.