Introduction: Optimal correction of hip dysplasia deformity with periacetabular osteotomy (PAO) that minimizes elevated contact stresses may reduce osteoarthritis (OA) development. Questions/Purposes: We used a computational approach based on discrete element analysis (DEA) to determine (1) if computational optimization can identify patient-specific acetabular corrections that optimize joint contact mechanics, (2) whether a strictly mechanically optimal correction is clinically feasible, and (3) whether the contact mechanics of optimal corrections differ from those of surgically achieved corrections. Methods: Preoperative and postoperative hip models were created from CT scans of a retrospective cohort (n=20) who underwent PAO to treat hip dysplasia. A digitally extracted acetabular fragment was computationally rotated in two-degree increments of lateral and anterior coverage to simulate candidate PAO reorientations. DEA-computed contact stress for each candidate reorientation model was used to select a purely mechanically optimal reorientation that minimized chronic contact stress exposures above damaging thresholds and a clinically optimal reorientation that balanced reducing chronic exposures with achieving clinically realistic acetabular orientations. Radiographic coverage, contact area, peak/mean contact stress, and peak/mean cumulative exposure were compared between preoperative, mechanically optimal, clinically optimal, and surgically achieved acetabular orientations. Results: Computationally optimal reorientations had significantly (p<0.001) more lateral and anterior coverage than surgically achieved PAO corrections. The mechanically/clinically optimal reorientations also had significantly more contact area (p<0.001/p=0.001) and significantly lower peak contact stress (p<0.001/p<0.001), mean contact stress (p<0.001/p=0.001), peak chronic exposure (p=0.001/p=0.003), and mean chronic exposure (p<0.001/p=0.001) than the surgically achieved corrections. Conclusions: This computational approach identified patient-specific mechanically optimal and clinically optimal acetabular reorientations. Surgically achieved reorientations did not reduce contact stress exposure to the extent achieved with computed optimal reorientations. However, optimal orientations identified for many patients risk secondary femoroacetabular impingement. Identifying patient-specific corrections that balance optimizing mechanics with clinical reality is necessary to reduce the risk of OA progression after PAO.

The institution of one or more of the authors (HDA, MT, MCW, JEG) has received funding from the Orthopaedic Research and Education Foundation. The institution of one of the authors (DJLR) has received funding from the National Institute of General Medical Sciences of the National Institutes of Health. RWW has or may receive payments or benefits from Smith and Nephew, Conmed, and Responsive Arthroscopy related to this work.

This study was funded by Orthopaedic Research and Education Foundation Career Development Grant 17-001 and the National Institute of General Medical Sciences of the National Institutes of Health Award Number R25GM058939.

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The Institutional Review Board (DHHS Registration # IRB00000099) of The University of Iowa (DHHS Federalwide Assurance # FWA00003007) gave ethical approval for this work (IRB ID # 201408762).

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