Infections of the bones and joints, al- though less common than infections in other parts of the body, are nonetheless significant clinical problems.

These infections generally fall into three broad categories: (1) infection of the joint (septic arthritis), (2) infection of the bone (osteomyelitis), and (3) soft-tissue or bone infection adjacent to a surgical implant or joint prosthesis. The presentation, pathophysiology, and treatment principles of each type of infection are distinct; thus, they will be described sepa- rately. Some rarer but still important types of musculoskeletal infection are described as well—namely, the musculoskeletal effects of human immunodeficiency virus (HIV) infection and other immunocompromised states, tuberculosis infections of the bone and joints, Lyme disease, and diabetic foot infections.

Bone and joint infections differ from infections in other parts of the body in three fundamental ways. First, the blood supply to bone and joint tissue is not as rich as that to most other tissues in the body. Although de- creased blood flow makes it more difficult for bacteria to reach skeletal tissues and cause infection, it also makes the elimination of established infections much more trouble- some. Second, the mechanical function of many joints is predicated on the precise geometry of the adjacent bones and cartilage surfaces. When this geometry is disturbed by infection, the function of a joint or even a system of joints may be compromised. For example, destruction of cartilage in even a small area of the knee as a result of septic arthritis can upset the mechanics of the knee, significantly interfere with walking, and possibly cause problems in other joints, such as the hip, ankle, or foot. Thus, treatment of musculoskeletal infections is imperative be- fore tissue destruction can occur.

Finally, the frequent use of surgical implants increases the risk of infection following many orthopaedic procedures. These materials disrupt the normal biologic environment. Even when the material is totally inert, the presence of foreign bodies allows bacteria to establish a nidus of infection.