Infection of Bones and Joints

Infection of a bone or joint implies that one or more species of bacteria have colonized the structure involved and are proliferating, causing a pathologic condition because of their presence. In the past, these conditions were termed osteomyelitis or infectious arthritis, and the treatment was not significantly different from case to case.1 The successful management of orthopedic infection necessitates distinguishing between the different anatomic locations and structures involved and adapting the most appropriate treatment methods. Therefore, categorization of orthopedic infections with regard to their mode of infection is helpful in determining prognosis and treatment. Orthopedic infections may originate from an endogenous or exogenous route. Endogenous infections are usually hematogenous, although occasionally septic lymphangitis can result in an infection of bones or joints.2 In exogenous infections, bacteria gain access to the affected site by external inoculation such as by direct trauma, injection, or surgical intervention. How infection is introduced can also influence the local blood supply, which, therefore, has a significant impact on the approach to treatment. With time, all orthopedic infections result in tissue destruction and loss of blood supply in the more central portions of the affected area, with hypervascularity occurring around the periphery. When possible, treatment is aimed at interrupting the process prior to local tissue destruction or abscess formation, and a careful assessment of the route of infection at the initial examination is helpful in approaching treatment. Hematogenous orthopedic infections are most common in the neonate in which the immune system is not fully developed. The most commonly involved sites are those at which bone growth is most active, such as the metaphyseal side of the physis. The artery enters and perfuses this area, and the venous return exits at 180° to retrace the same path as the arterial circulation.3 This hairpin-loop capillary bed facilitates bacterial attachment, multiplication, and thrombosis of the vessels. Septicemia is common in neonates and may result from gastrointestinal absorption or infection of the umbilicus. Circulating bacteria have access to all tissues, but bone and joint tissues are particularly vulnerable because of their vascular anatomy. Hematogenous orthopedic infections are rare in adults because the vascular anatomy changes with skeletal maturity. The site of hematogenous localization is often on the metaphyseal side of the physis, which has abundant capillary loops to support bone growth (Fig. 1). A similar vascular organization exists in the subchondral bone of the articular cartilage and the underlying growth cartilage of the epiphysis. An epiphyseal infection can often lead to ORTHOPEDIC