TP4.3 Accuracy of Patient Specific Guide to Achieve Pre-Operatively Templated Correction of Hip Dysplasia with PAO

Abstract

Abstract Objectives Patient-specific instrumentation is available to guide correction of hip dysplasia with periacetabular osteotomy (PAO). Accuracy of the guides used to achieve a pre-operatively templated correction has not been critically assessed. The goal of this work was to compare the accuracy of the Medacta MyPAO system to position the acetabular fragment in a pre-operatively templated position. Methods Ten patients (average age 20.6 years, n=10 female) underwent PAO to treat hip dysplasia. Each patient’s correction was planned from CT images using the MyPAO system by Medacta. Patient-specific guides were used intraoperatively to achieve the correction, and a pelvis CT was collected 2 days after surgery. Postoperative CT scans were segmented in Materialise Mimics, and the resulting 3D surface models were imported into Geomagic Design X for orientation into an anatomy-based coordinate system. The surface model of the planned correction was aligned to the postoperative hip by surface matching the non-acetabular region of the pelvis. Differences in hip center between the planned and actual postoperative correction were calculated as the difference between centers of spheres fit to the weight-bearing acetabular subchondral bone. After adjusting to align acetabular centers, a custom algorithm was used to calculate acetabular coverage in 1-degree increments around the acetabular rim. These were binned into relevant anatomic regional coverage assessments. Results The postoperative acetabular center ranged from 1.4 mm posterior to 3.2 mm anterior to, and up to 3.1 mm inferior to the planned acetabular center. The postoperative center was lateral to the planned center in 8/10 hips (by up to 9.3 mm). Coverage was within an average of 1.9±1.6° in the anterior acetabular region, 3.0±2.1° in the anterior superior region, and 3.2±2.9° in the superior region. Coverage differences between planned and postoperative correction were greatest in the posterior superior (5.5±4.2°) and posterior (8.4±9.0°) regions. Conclusion Intraoperative PAO guidance hardware appears to be useful for achieving targeted coverage corrections at multiple locations around the acetabular rim. Advances in these systems will be needed to improve postoperative agreement with planned joint center location and the ability to achieve the templated posterior coverage.