Deformation of press-fitted metallic resurfacing cups. Part 1: Experimental simulation

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Materials Science

Background:

• Metal-on-metal hip resurfacing uses a one-piece acetabular cup.
• Cup deformation during press fit can affect implant stability and performance.
• Accurate laboratory models are needed to simulate in-vivo conditions.

Purpose of the Study:

• To experimentally investigate the interference press fit and deformation of metallic acetabular cups.
• To establish a reliable laboratory model simulating pelvic bone support for acetabular cups.
• To determine the influence of cup design parameters on acetabular cup deflection.

Main Methods:

• Cadaver tests were used to validate a polyurethane foam model representing pelvic bone quality.
• A two-point loading model simulating worst-case pelvic forces was developed.
• Acetabular cup deformation was measured under varying wall thickness and interference fit conditions.

Main Results:

• The validated foam model accurately replicated cadaver test conditions for cup deformation.
• Cup deflection was highly sensitive to wall thickness and diametral interference.
• A thin cup (2.3-4 mm wall) with 0.5 mm interference showed ~60 microm deflection.
• Thickening the cup and lateralizing reduced deformation to 30-50 microm.

Conclusions:

• Acetabular cup wall thickness and interference fit are critical factors influencing press-fit stability.
• Optimizing cup design parameters can minimize potentially harmful cup deformation.
• The developed laboratory protocol provides a reliable method for studying acetabular cup biomechanics.