Objectives: After total hip arthroplasty (THA), restoration of hip center of rotation (COR) is essential to ensure stability of the prosthetic hip and longevity of the prosthesis. Our aim was to determine whether, and how, the COR changed postoperatively compared to the native COR following implantation of a cementless acetabular component in anatomical position and to compare the accuracy of cup placement between two surgeons with different levels of surgical experience.
Materials and methods: We evaluated 145 patients (145 hips) who underwent unilateral primary THA, who had no distorted acetabulum on the affected hip and a normal contralateral hip. Hip reconstruction was radiologically and clinically assessed at a minimum 2-year follow-up. Perioperative change in COR, initial cup position, offset, leg-length discrepancy (LLD), radiographic cup orientation, Harris Hip Score (HHS), component loosening, and dislocations were compared between the highly experienced surgeon and less-experienced surgeon groups.
Results: The COR was significantly displaced in the superior and medial directions postoperatively. Significant differences were identified in the vertical COR change, initial cup position, LLD, cup inclination, and cups within safe zones, but not in the horizontal COR change, offset parameters, cup anteversion, or HHS. There were no radiographic evidence of component loosening in both groups, but three dislocations (7%) only in the group operated on by the less-experienced surgeon (p = 0.027).
Conclusions: We found that the postoperative COR tended to be displaced in the superior and medial directions, and that the level of surgical experience strongly affected the accuracy and consistency of cup placement, particularly in COR position and cup inclination.