Determination of reference geometry for polyethylene tibial insert wear analysis

Area of Science:

• Biomedical Engineering
• Materials Science
• Orthopedic Surgery

Background:

• Geometric wear analysis necessitates unworn geometries as references.
• Retrieval studies often lack access to pristine, never-implanted geometries.
• Accurate reference models are crucial for precise wear quantification in orthopedic implants.

Purpose of the Study:

• To develop and validate a method for creating reference geometrical models from available never-implanted tibial inserts.
• To assess the variability introduced by using averaged geometries as references.
• To compare reference variability with manufacturing variability.

Main Methods:

• Micro-computed tomography (micro-CT) scanning of never-implanted tibial inserts.
• Coalignment and averaging of 2, 3, or 6 insert surfaces to generate reference geometries.
• 3D deviation analysis comparing individual inserts to each other and to the generated reference geometries.

Main Results:

• The developed method successfully created reference geometries with reduced reference variability (8.3 ± 39 μm).
• Manufacturing variability was found to be 15 ± 59 μm.
• Smallest deviations were observed on articular surfaces, significantly less than the typical insert wear rate (20 μm/y).

Conclusions:

• The proposed method provides a reliable approach to establish reference geometries for wear analysis in the absence of unworn originals.
• This technique minimizes reference variability, enhancing the accuracy of wear measurements in retrieved orthopedic implants.
• The findings support the use of this method for robust geometric wear analysis in retrieval studies.