A scanning electron micrograph (SEM) of cancellous (spongy) bone from an osteoporosis patient. Osteoporosis is characterized by increased brittleness of the bones and a greater risk of fractures. This is reflected here in the thin appearance of the bony network of the cancellous bone that forms the core of the body's long bones. (Photograph by P. Motta, Photo Researchers, Inc. Reproduced by permission.)