Independent evaluation of a patient specific system for acetabular cup placement in total hip arthroplasty

The impact of the spinopelvic relationship on hip instability and impingement after total hip arthroplasty (THA) has led to growing interest in functional acetabular component position. Various surgical techniques and technological advancements have been introduced to optimize acetabular component placement by accounting for individual spinopelvic mobility patterns. The purpose of this study was to evaluate the accuracy of acetabular component positioning with the use of a patient specific instrument (PSI).

A consecutive series of 188 THAs performed between 2017 and 2021 was retrospectively reviewed. A preoperative analysis using a commercially available system utilizing dynamic preoperative spinopelvic imaging was utilized to determine individualized functional acetabular component position (anteversion and inclination) and generate an acetabular patient specific instrument incorporating that target orientation. The incidence of postoperative inclination and anteversion errors >5° and 10° versus the desired preoperative plan was determined using a validated ellipse fitting algorithm.

97.3% (183) and 96.3% (181) of acetabular components were positioned within 10° of the anteversion and inclination targets, respectively. 92.6% (174) simultaneously met both targets. 80.9% (152) and 75.0% (141) were within 5° of the anteversion and inclination targets, respectively. 59.0% (111) simultaneously met both targets. The mean absolute error (difference between plan and postoperative measurements) for inclination was 4.11° ± 3.12° (range 0.05°- 17.5°) and for anteversion was 3.38° ± 2.68° (range 0.01° - 12.3°).

This system reliably facilitates positioning of acetabular component inclination and anteversion to within 10° of the targeted plan. Outliers increased when the error value was limited to 5° but still provided accurate placement in nearly 60% of patients for inclination and greater than 80% of patients for anteversion. Further research is warranted to assess the clinical impact and cost effectiveness of improved component placement in an individualized functional position with patient specific guides.