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Septic arthritis, the invasion of the synovial membrane by microorganisms, usually with extension into the joint space, is generally secondary to infection elsewhere in the body. In young adults, the primary infection is generally a genital lesion caused by Neisseria gonorrhoeae. In all other age groups the most common agent is Staphylococcus aureus, which spreads from a cutaneous lesion. Several other agents may cause septic arthritis but their frequency of infection is low.


There is no microorganism that shows a tropism for synovial membrane and/or joints. During a septicemia, caused by an infection at a site outside of the joint, organisms are deposited in or on the synovial membrane and only rarely proliferate to cause a septic arthritis. When they do grow, the infection may spread to the joint space and then spread to bone and cartilage.


When joint infection occurs as a result of bacteremia, the initial growth of microorganisms is either in the synovial membrane or in the adjacent bone. In either case, an inflammation of the synovial membrane is quickly established and results in a marked increase in leukocytes in the synovial fluid, even though the fluid itself is sterile. When the microorganisms have spread into the joint fluid, culture of the fluid reveals the etiology of the infection. The pathologic findings are varied and depend on the duration of the infection, the organism and the resistance of the host. Early in the infection, only inflammatory changes in the synovium are seen. Late in the course of untreated septic arthritis, destruction of joint structures is marked. Articular cartilage is particularly vulnerable because it is an avascular tissue.

In acute, pyogenic arthritis, the cartilage characteristically dissolves first at points of articular contact to expose the underlying bone. As destructive changes occur several abnormalities appear in the synovial fluid:

Increased pressure

Low pH

Low concentration of glucose

Activation of proteolytic enzymes

Increased turbidity

Presence of mucin precipitate


The clinical manifestations of septic arthritis are variable and related to many factors: the etiologic agent, the joint involved and the age of the patient. In gonococcal arthritis one sees:

A prominent prodrome consisting of fever, chills, headache, anorexia and malaise

Migratory polyarthralgia or polyarthritis prior to localization in one or more joints

Skin lesions of gonococcemia

Small joint effusions

Tenosynovitis in about 1/3 of patients

Large joints are most involved

In nongonococcal septic arthritis the clinical picture is variable. At one extreme, the patient may complain of an acutely painful, swollen joint that is exquisitely tender and rigidly limited in range of motion but no manifestations of infection elsewhere. At the other extreme there may be little or no signs of inflammation.


The definitive diagnosis of septic arthritis requires examination of the synovial fluid. This fluid will show:

Presence of microorganisms

Presence of antibody directed against the microorganisms


More than 10,000 pmns/mm3

Decreased glucose concentration (< 0.6% of blood glucose)

Increased lactic acid concentration (> 65 mg/dl)


Treatment consists of both drainage of the synovial fluid and administration of an antibiotic systemically. Antibiotic choices include ceftriaxone, cofotaxime and ceftizoxime.

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