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. The overall goal of the parent R01 project is to rigorously investigate how periacetabular osteotomy changes hip biomechanics and how those changes are associated with patients’ activity levels and self-reports of function, pain, and quality of life during the first year after surgery. This supplement request in response to PA-23-189: Research Supplements to Promote Diversity in Health-Related Research (Admin Supp Clinical Trial Not Allowed) will support the training and career development for a PhD student whose long-term goal is to be a senior-level independent investigator at the crossroads of biomechanical engineering, orthopedics, and movement science. The supplement scholar will enhance the impact of the parent R01 by investigating the morphology and biomechanics of the contralateral hip in patients with DDH who receive PAO. Many patients present with bilateral evidence of DDH but only unilateral symptoms. After PAO, half of patients develop contralateral hip symptoms and thirty percent receive hip preservation surgery. Thus, the contralateral hip is an important component in the overall treatment of patients with DDH and in our understanding of DDH as an osteoarthritis precursor. The supplement scholar will also receive customized training and mentoring to foster her growth as a scientist. It is expected that this supplement will provide the scholar foundational training to progress to her next career step and enable her to advance as an important voice of under-represented senior investigators in the biomedical sciences.