Abstract
Introduction
All hip replacements depend upon good orientation and positioning to ensure that implants function well in vivo. Mal-orientated devices can lead to poor patient gait, poor range of motion, impingement, edge loading and high wear, which in turn may result in the premature failure of the implants.
Aim
To investigate the correlation between edge loading and wear on retrieved implants through linear wear analysis and radiographic examination of implants in vivo.
Materials & Methods
55 BHR retrieved acetabular cups with known times in vivo were examined. Linear wear analysis was conducted using a Taylor-Hobson Talyrond 290 roundness machine. Edge loaded cups were classified as cups which showed the wear area crossing over the edge of the cup. Non-edge loaded devices were devices with the wear area within the articulating sphere of the cup, Figure 1. The maximum deviation of the profile from an ideal circle was taken as the maximum linear wear. The implant orientation angles for one edge loaded acetabular component was determined by superimposing BHR models, generated by ProEngineer Wildfire 4 with ISDX II extension software, onto frontal x-ray images, Figure. 2.
Results
In this study 32 cups were classed as edge loaded and 23 classed as non-edge loaded. Non-edge loaded cups had a linear wear rate of 1.48±1.01 μm/year. Edge loaded cups generated a significantly higher linear wear rate of 24.02±22.72 μm/year than non-edge loaded devices. For the device analysed radiographically, the inclination was 62° and version angle was 16°. The inclination angle of this device is outside the recommended inclination angle for the BHR and would be considered as mal-orientated. The linear wear result showed that the device was edge loaded with a wear rate of 22.25 μm/year.
Discussion/Conclusion
This study aimed to find a correlation between edge loading and high wear of retrieved devices. The results in this study show that edge loaded bearings generate significantly higher linear wear rates compared to the non-edge loaded group. The devices in the edge loaded group also showed a greater scatter with unpredictable linear wear.
