Volumetric wear analysis of polyethylene tibial inserts in artificial knees

Advances in artificial knee designs have made polyethylene (PE) wear the limiting factor in the life of total knee systems. Major surgery may be avoidable if the condition of the plastic part of an artificial knee system can be determined by establishing a correlation between the size, shape or number of PE particles detected in synovial fluid samples to the volumetric wear of the plastic tibial insert. METHODS: PE debris in the synovial fluid of four damaged knees, each from a different human subject was collected by aspiration, and subjected to base digestion and ultrafiltration. The particles were then scanned using scanning election microscopy (SEM) and analyzed using NIH Image version 1.58. The volume for the remaining worn PE inserts were calculated by Application Service Company (ASC), Corcoran, MN, using laser technology. Relationships between volumetric wear loss and particle area and morphologies were then examined. RESULTS: The shape of the PE particles analyzed by SEM were categorized as globular, fibrous or flakes. The average percent globular, fibrous and flake particles for all patients were 85.73, 7.22, and 6.98 respectively. The average areas of the globular, fibrous and flake debris were 89.02μm∧2, 410.46μm∧2 and 512.07 μm∧2 respectively. The total wear of each implant determined by laser analysis for the four patients were from 1.86% to 13.74%. CONCLUSIONS: Preliminary indications from this small sample set suggest that there is no correlation between shape or number of PE particles and volumetric wear. The area of the globular particles increased slightly with increased volumetric wear.