Basic Sciences of Bone and Joint Diseases

The bone develops by intramembranous and endochondral ossification. Intramembranous ossification occurs through the transformation of mesenchymal cells into osteoblasts, while in endochondral ossification, a preexisting cartilage forms first and then undergoes ossification. Two types of bone tissues form the skeleton: compact or cortical bone and cancellous, trabecular, or spongy bone. The spongy bone has a turnover rate approximately eight times greater than that of cortical bones. The bone is formed of three types of cells: osteoblasts, which produce the organic bone matrix; osteocytes, which produce the inorganic matrix; and osteoclasts, which are responsible for bone resorption. The bone marrow converts into yellow, or inactive, marrow, gradually reaching an adult pattern by the age of 25. The yellow marrow may reconvert due to the stress associated with several pathological and physiological processes. Joints develop in the mesenchyme between the ends of bones and are classified into several types according to their functional features as well as the nature of the adjoining tissue. The principal response of the bone to injury, and disease, is reactive bone formation; this is the basis of increased uptake of bone-specific radiopharmaceuticals, namely, Tc-99 m diphosphonates and F-18 sodium fluoride. Other specific bone and joint pathological changes define the patterns of uptake of other radiopharmaceuticals used for imaging such diseases [e.g., gallium-67, labeled leukocytes, thallium-201, Tc-99 m methoxyisobutylisonitrile (MIBI), and F-18 fluorodeoxyglucose (FDG)]. The factors that ensure the best possible quality and interpretation of radiopharmaceutical investigation include obtaining the relevant clinical information, proper preparation of the patients (including sedation of pediatric patients), meticulous positioning of patients and adequate acquisition, familiarity with the normal appearance in different age groups (and normal variants), awareness of the technical pitfalls, and the strengths and limitations of each modality.