PROJECT SUMMARY / ABSTRACT Developmental dysplasia of the hip (DDH) is a life-long disorder that alters joint biomechanics and increases the risk of early osteoarthritis. The most common treatment for DDH is periacetabular osteotomy (PAO), which surgically reorients the abnormally shaped acetabulum to better cover and stabilize the femoral head. After PAO, patient reported outcome measures (PROMs) improve for many, but not all, patients, and PROMs for most patients remain below the levels of their healthy peers. Recent work has shown that aberrant biomechanical variables, including disproportionate joint reaction forces, high acetabular edge loads, and low abductor muscle strength, are related to specific geometric deformities in DDH prior to PAO. These altered biomechanics are also related to worse PROMs. The current project seeks to optimize surgical care for DDH by determining the effects of, and relationships among, PAO-induced changes to hip geometry, biomechanics, and PROMs. Aim 1 will assess how PAO-induced changes in bony geometry alter hip biomechanics. Geometric and biomechanical profiles for patients (N=60) undergoing PAO will be established before surgery using magnetic resonance imaging, motion capture, and musculoskeletal modeling. Changes to patients’ biomechanical profiles resulting from PAO-induced changes to geometry will be determined at 6 and 12 months post-PAO. Aim 2 will establish target ranges for PAO surgical correction based on the sensitivity of biomechanical outcomes to variability in acetabular reorientation. Surgically feasible combinations of changes to patients’ acetabular geometry will be tested using probabilistic analysis, musculoskeletal models, and high-throughput computing to predict the resultant changes to biomechanics. Aim 3 will determine the relationships among PROMs, activity levels, and biomechanics pre-PAO and over the first 12 months post-PAO. Electronic questionnaires and wearable sensors will be used to monitor PROMs and activity changes as patients recover from surgery. From these data, we will demonstrate how hip biomechanics and activity levels differ in patients with improved PROMs compared to those with unresolved symptoms. Results from the project will inform customized surgical plans according to patients’ initial bony geometry and help surgeons and patients focus on modifiable treatment factors that are associated with improved outcomes. Likewise, new information about variables such as post-PAO activity levels and muscle strength will inform rehabilitation to further improve outcomes. Finally, this project will pave the way for long-term longitudinal analyses of PROMs, biomechanics, and joint structure to inform surgical and rehabilitation approaches that predictably mitigate early hip osteoarthritis.