Mechanical evaluation of taper assembly

Presenting Author - Qurashi Sol
Introduction & aims Fixation between the femoral head and taper is fundamental in total hip arthroplasty. Surgical technique can influence the ability to impact a femoral head at the time of surgery. We evaluated static pull off after cyclical loading of a femoral head placed on the taper under conditions of dry and wet and with and without impaction.Method The surface profiles of 16 CoCr tapers and femoral heads were characterized at four sites before and after testing. Four assembly conditions were examined: Dry or Wet Tapers; No impaction or Impaction (n=4 per group). An additional sample per group was assembled and sectioned to examine the taper and femoral heads. Impaction with a metal tip with one hammer blow was performed by a single surgeon. Samples were loaded for 500 cycles between 250 – 2500 N at 1Hz and pull-off at 0.008 mm/second. Peak loads were compared between groups and surface damage using surface roughness (Ra, Rz) and scanning electron microscopy (SEM).Results Mean impaction force of 622 N was used in this study. No differences were detected under dry conditions and cyclically loading with a single impaction during assembly. A single impaction to a wet taper resulted in a greater pull-off force compared to a dry taper. Differences were detected in Ra of the tapers and Rz of the heads before and after testing. SEM revealed areas of focal damage at the contact surfaces. Conclusions Pulling a head off a taper alters the surface of both. Cyclically load after assemble provided a robust taper-head interface.