This study focuses on people who have a long bone defect (LBD), which is defined as a loss of bone tissue in any long bone of the arm or leg. Reconstructive surgery is often required. The purpose of the study is to set up an international, multicenter registry of patients presenting with defects in long bones. With this observational registry, researchers aim to learn more about how various reconstruction surgeries are done in other countries and their outcomes. Participation will not change anything in the patient’s surgery and will follow standard-of-care practice. Medical records and questionnaires will be reviewed and placed in a repository. Researchers hope that the information from this registry will help improve the treatment or management of other patients with LBD.