Ceramic Heads in Total Hip Replacements: Surgical Impaction Force and Retrieved Implant Damage Assessment

Total hip replacement (THR) is commonly performed to relieve arthritis or traumatic injury. However, implant failure can occur from loosening or crevice corrosion resulting from inadequate seating during implantation. The objective of this study was to evaluate the differences in surgical assembly force considering two materials—metal and ceramic heads—while ascertaining effects of surgeon experience. A second aim was to assess damage features of retrieved ceramic head implants. A total of 32 surgeons of varying levels were recruited and asked to perform a benchtop, modular taper assembly simulating an operating room procedure. The apparatus comprised of a 12/14 stem taper attached to a 3-dimensional force sensor (9347C, Kistler® USA, Amherst, NY). Surgeons were assigned a metal or ceramic femoral head and instructed to assemble the taper using their preferred technique. Surgeons were brought back to test the opposite material after four weeks. For the second aim, 25 retrieved hip implants were collected and the heads, stem tapers, and head tapers were studied using the RedLux Metrology Optical Coordinate Measuring Machine (Ortholux, RedLux, Ltd, Romsey, UK). The stem tapers were also analyzed with scanning electron microscope and Zygo 3D Optical Surface Profiler (Zygo Corporation, Middlefield, CT) machines. Results suggest no significant differences between forces applied to metal and ceramic heads. Attending surgeons exhibited the lowest variability among the different surgeon groups and applied their force with the smallest off-axis angle. Lastly, the impaction force plots suggest that the first impact strike is the most crucial for head stability. The retrieved ceramic head implants showed evidence of fretting and crevice corrosion as well as plastic deformation and material transfer from the stem to the head. Differences in impaction force when assembling metal and ceramic femoral heads were not apparent; however, variability of technique and force was observed across experience levels and within surgeons of the same level. The damage features found on the ceramic implants could indicate how well the head was seated on the taper, a result of surgical impaction force during implantation. Understanding assembly mechanics and surgical habits for THR will provide insight to the best assembly procedures.