Patient-Specific Acetabular Safe Zones in Total Hip Arthroplasty: External Validation of a Quantitative Approach to Preoperatively Templating Spinopelvic Parameters

Background: Spinopelvic mechanics are critical in total hip arthroplasty; however, there is no established consensus for adjusting acetabular component positioning based on spinopelvic parameters. This study aimed to (1) validate a recently developed Patient-Specific acetabular safe-zone calculator that factors in spinopelvic parameters and (2) compare differences with hip-spine classification targets. Methods: A total of 3750 patients underwent primary total hip arthroplasty across 3 academic referral centers, with 33 (0.88%) requiring revision for instability. Spinopelvic parameters were measured before initial total hip arthroplasty, and acetabular component position was measured following the index and revision procedures. Most operations employed either computer navigation or robotic assistance (94%). Surgical approaches included both anterior and posterior techniques. Utilizing our recently developed patient-specific safe-zone calculator, theoretical intraoperative positions were calculated and compared to true component positions before and after revision. Results: Among 33 patients who underwent revision, none dislocated at an average follow-up of 5.1 years. In the external validation cohort, the average absolute differences between the patient-specific safe-zone and the median hip-spine classification recommendation were 3.8 degrees +/- 2.1 degrees inclination and 5.0 degrees +/- 3.2 degrees version. For the pooled cohort, the absolute differences between the patient-specific safe-zone targets and the prerevision component positions were 7.9 degrees +/- 5.1 degrees inclination and 11.4 degrees +/- 6.9 degrees version. After revision, the mean absolute differences decreased to 3.6 degrees +/- 3.1 degrees inclination and 5.8 degrees +/- 3.5 degrees version (P < .001). Conclusions: A patient-specific approach improved acetabular component positioning accuracy within 6 degrees of version and 4 degrees of inclination of stable, revised hips. Patient-specific safe zones provide quantitative targets for nuanced spinopelvic preoperative planning that may mitigate risk of instability and may indicate use of assisted technologies. (c) 2024 The Authors. Published by Elsevier Inc. on behalf of The American Association of Hip and Knee Surgeons. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).