We dedicate this text to Drs. Ernest E. Aegerter, a pathologist, and John A. Kirkpatrick Jr., a radiologist. They were among the principal founders of the ?eld of skeletal pathology and radiology. During their time, their residents and colleagues knew them as great educators with a dedication and a passion for their work. Their textbook, Orthopedic Diseases, published initially in 1958 was among the ?rst interdisciplinary works devoted to this ?eld. Dr. Aegerter and Dr. Kirkpatrick illuminated many aspects of the ?eld of radiology. Today, with the advent of new technologies, this ?eld has grown to include not only diseases that affect the skeleton but also those that affect muscles, ligaments, tendons, and also the cartilaginous structures within joints. With this text we intend to carry on Dr. Aegerter and Dr. Kirkpatrick's tradition. We have recruited only well-known musculoskeletal radiologists and pathologists to participate in the writing of this book. Each author has been carefully selected for his expertise on the topic about which he's been asked to contribute. Each author is known as an experienced and seasoned teacher. Each author has made a mark on the ?eld.