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:
Low concentration of glucose
Activation of proteolytic enzymes
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
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
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.