23. Major co-morbidities: alcohol or drug abuse, illnesses that affect bone or calcium metabolism, connective tissue disorders, coronary artery disease, severe ischemic heart disease [New York Heart Association Class III or IV], previous myocardial infarction, severe pulmonary disease [forced expiratory volume <50% of normal], diabetes mellitus (Type I or Type II), immunosuppression, peripheral vascular disease, severe penetrating or hemorrhagic traumatic brain injury, a history of skeletal malignancies, prior external beam or implant radiation therapy involving the skeleton.