Method for the location of primary wear scars from retrieved metal on metal hip replacements

BACKGROUND Retrieved metal-on-metal acetabular cups are valuable resources in investigating the wear behaviour of failed hip implants, but adequate methods to do so are lacking. To further contribute to addressing this issue, we developed a method to detect the in vivo location of the primary wear scar of an explanted cup. METHODS We proposed a new method in which thirteen patients with failed metal hip resurfacings were recruited, and their acetabular components retrieved. A 3D wear map was generated and the precise location of the primary wear scar in each cup was identified using a coordinate measuring machine. This wear scar location was noted in relation to the features on the acetabular cup. Having identified the location of the wear scar, this 3D positional map was co-registered to the implant on the patient's pelvic 3D CT scan. RESULTS Using our proposed technique, we were able to demonstrate that the in vivo position of the primary wear scar in explanted metal acetabular cups can be variable. CONCLUSIONS This method has utilised existing techniques to better understand the three-dimensional properties of wear behaviour, and may be a method which can be used in further studies to investigate variables that affect the position of the primary wear scar.