The purpose of this clinical research study, “Total Hip Replacement at HSS in Subjects under 35 Years of Age: Retrospective Chart Review and Patient Follow-up,” is to evaluate the survivorship of total hip arthroplasty (THA) in patients under 35 years of age, as well as to evaluate their functional levels. Ultimately, this information will help us to improve implants for patients, many of whom currently require custom implants due to unusual bone development. We have identified and reviewed charts on 711 patients (952 hips) performed at HSS since 1988. Patients under 35 who receive hip replacements have a wide variety of diagnoses, with the leading diagnoses being avascular necrosis, inflammatory arthritis, and developmental dysplasia of the hip. We have completed chart review for all patients and have begun to obtain follow-up and survivorship data on those patients with AVN and JIA. We will analyze and collect X-ray data on those patients with altered pathoanatomy (JIA, DDH and skeletal dysplasia). The medical student involved in this project will work to contact patients and collect follow-up data on survivorship, pain, and mobility. The student will prepare data for analysis and will present a talk at the completion of his rotation. The student will have the opportunity to attend daily educational conferences as well as scrub in the OR with Dr. Figgie.