A novel preoperative prosthetic position planning algorithm for total hip arthroplasty based on the no-impingement principle: A case study

Most preoperative planning calculations of impingement-free range of motion (IFROM) and impingement-free safe zone (IFSZ) rarely consider non-standard shaped prostheses and bony impingement (BI) for total hip arthroplasty (THA). This research developed a novel algorithm that considers BI, prosthetic impingement, pelvic tilt angle (<i>PT</i>) in the sagittal plane, and non-standard-shaped hip prostheses. This research aimed to investigate the effect of BI and <i>PT</i> on hip IFROM, IFSZ, and the BI rate. Using this algorithm to calculate a case, we found that when considering BI, (1) the upper limit of the hip IFROM was decreased, and the different <i>PT</i> affected the upper limit of the hip IFROM of various movements; (2) the BI rate of the flat-rim liner in standing and sitting postures were 54.6% and 67%; and (3) the maximum IFSZ size of the flat-rim liner was reduced by 12%, the reduction rate of the combined pelvic position with a non-zero IFSZ size was 83.2% for the flat-rim liner. Consideration of BI further reduces the IFROM, the IFSZ size, and the number of the combined position of the pelvis with a non-zero IFSZ size of the hip joint. Importantly, this algorithm provides a reliable tool for personalized prosthesis positioning for THA. This algorithm has excellent applications in personalized surgical planning and surgical robotics.