Septic arthritis, as the name implies, is a septic inflammatory lesion of the joint, which has these three main x-ray manifestations: 1. Bone destruction of the joint. The area of the joint surface shows worm-like or irregularly shaped, diffuse, and limited bone destruction. This destruction can be seen with dead bone of varying sizes, and this dead bone can be free into the joint cavity; 2. Significant narrowing of the joint space. The destruction of the joint surface, articular cartilage, and subchondral bone results in a marked narrowing of the joint space; 3. A large amount of fluid is present in the joint cavity. This effusion is inflammatory pus, which may be interspersed with free dead bone.