Radiographically successful periacetabular osteotomy does not achieve optimal contact mechanics in dysplastic hips

Background: Optimal correction of hip dysplasia via periacetabular osteotomy may reduce osteoarthritis devel-opment by reducing damaging contact stress. The objective of this study was to computationally determine if patient-specific acetabular corrections that optimize contact mechanics can improve upon contact mechanics resulting from clinically successful, surgically achieved corrections.Methods: Preoperative and postoperative hip models were retrospectively created from CT scans of 20 dysplasia patients treated with periacetabular osteotomy. A digitally extracted acetabular fragment was computationally rotated in 2-degree increments around anteroposterior and oblique axes to simulate candidate acetabular reorientations. From discrete element analysis of each patient's set of candidate reorientation models, a me-chanically optimal reorientation that minimized chronic contact stress exposure and a clinically optimal reor-ientation that balanced improving mechanics with surgically acceptable acetabular coverage angles was selected. Radiographic coverage, contact area, peak/mean contact stress, and peak/mean chronic exposure were compared between mechanically optimal, clinically optimal, and surgically achieved orientations.Findings: Compared to actual surgical corrections, computationally derived mechanically/clinically optimal reorientations had a median[IQR] 13[4-16]/8[3-12] degrees and 16[6-26]/10[3-16] degrees more lateral and anterior coverage, respectively. Mechanically/clinically optimal reorientations had 212[143-353]/217 [111-280] mm2 more contact area and 8.2[5.8-11.1]/6.4[4.5-9.3] MPa lower peak contact stresses than sur-gical corrections. Chronic metrics demonstrated similar findings (p <= 0.003 for all comparisons).Interpretation: Computationally selected orientations achieved a greater mechanical improvement than surgically achieved corrections; however, many predicted corrections would be considered acetabular over-coverage. Identifying patient-specific corrections that balance optimizing mechanics with clinical constraints will be necessary to reduce the risk of osteoarthritis progression after periacetabular osteotomy.