Centre of rotation in total hip arthroplasty: a critical review with emphasis on three-dimensional planning.

Accurate restoration of the centre of rotation (CoR) is crucial for the long-term success of a total hip replacement (THR); however, cup positioning remains one of the major challenges of this procedure. The aim of this study was to critically review the existing literature documenting CoR planning in THR. Specifically: 1. The rationale behind component placement; 2. The benefits and limitations of the current techniques used; and 3. Future directions and their application to clinical practice. Traditional two-dimensional (2D) templating, although widely used, has limited accuracy due to magnification errors and variability in patient positioning. Three-dimensional computed tomography (3D-CT) preoperative planning allows for a more precise estimation of CoR. Integration with robotic systems enables intraoperative execution of the plan but comes with high costs and a steep learning curve. Patient-specific instrumentation (PSI) provides a cost-effective alternative. Meanwhile, surgeon experience and intraoperative judgement remain crucial, particularly in patients with abnormal anatomy or deformities. Restoration of CoR within approximately 5 mm of the planned medial and superior position has been associated with improved biomechanical performance and implant longevity. While 2D templating can achieve this in most routine cases, 3D planning, robotic-assisted surgery, and PSI allow for more accurate placement. This is particularly useful in complex cases, such as revisions or developmental dysplasia of the hip, where the risk of clinically significant deviations remains high and more targeted surgical strategies are needed.