Particles and Ions Generated in Total Hip Joint Prostheses: In Vitro Wear Test Results of UHMWPE and XLPE Acetabular Components

The accurate and detailed characterization of wear particles and ions released from total hip joint prostheses is essential to understand the cause and development of osteolysis, aseptic loosening and hypersensitivity. In this in vitro research, the wear particles and ion release of 22 different test liquids from hip simulator studies were investigated. Wear particles generated from acetabular components made of ultra-high-molecular-weight polyethylene (UHMWPE) or cross-linked polyethylene containing vitamin E (XLPE) were compared using scanning electron microscopy (SEM) and laser diffraction. Additionally, the effect of running-in versus steady-state, accelerated ageing, head materials and calcium sulphate third-body particles on the morphology and size of the created debris was investigated. The Fe, Ni, Mn, Nb, Co, Mo and Al ions released from femoral heads made of stainless steel, CoCrMo and alumina ceramic were analysed using inductively coupled plasma mass spectrometry. The combination of SEM and laser diffraction to analyse both the morphology and the particle-size distributions of the polyethylene wear particles was very powerful. The wear particles were predominantly in the submicron range and globular, with occasional fibrils. The size distributions of the UHMWPE and XLPE particles were similar; however, more fibrils were observed among the UHMWPE particles. The average particle size decreased for most samples in the steady-state phase compared to the running-in. The accelerated ageing and the presence of third-body particles generally caused larger UHMWPE wear particles only. Increasing the size of the stainless steel femoral heads led to an increase in the ion level too.