An infection in the joint almost always secondary to infection at some other site of the body. The bacteria enters the joint from the bloodstream, from a contiguous site of infection in bone or soft tissue. In traum, surgery or invasive procedures, the bacteria might directly be inoculated in the joint, or by direct inoculation during surgery, injection, or trauma.
Synovial capillaries, lack the natural barrier of basement membrane which allows infiltration of the joint with bacteria. Within hours neutrophilic reaction begins in the synovium,the membrane that lines the joint.
Neutrophils and bacteria enter the lumen of the joint, and bacteria adhere to articular cartilage.
Degradation of cartilage begins within 48 hour due to following factors
- Increased intraarticular pressure
- Release of proteases and cytokines from chondrocytes
- Invasion of the cartilage by bacteria and inflammatory cells.
Synovial proliferation results in the formation of pannus over the cartilage, and thrombosis of inflamed synovial vessels develops.
In infants, group B streptococci, gram-negative enteric bacilli, and S. aureus are the usual pathogens. S aureus and streptococcus pyogens (group A streptococcus) are major pathogens after vaccine against H influenzae.
N. gonorrhoeae is the most commonly implicated organisms in young adults. S. aureus accounts for most nongonococcal isolates in adults of all ages and gram negative bacilli, pneumocci are involed in up to one third of cases in older adults, especially those with underlying comorbid illness.
Infections following surgical procedures or penetrating injuries are due most often to S. aureus and occasionally to the gram-positive bacteria or gram-negative bacilli.
Infections with coagulase-negative staphylococci are unusual except after the implantation of prosthetic joints or arthroscopy.
Anaerobic organisms, often in association with aerobic or facultative bacteria, are found after human bites and when decubitus ulcers or intraabdominal abscesses spread into adjacent joints.
Polymicrobial infections complicate traumatic injuries with extensive contamination. Cat bites or scratches may introduce Pasteurella multocida into joints.
Ninety percent of patients present with involvement of a single joint. Among intravenous drug users, infections of the spine, sacroiliac joints, or sternoclavicular joints are more common than infection of the appendicualr skeleton. Polyarticular infection is most common among patients with rheumatoid arthritis and may resemble a flare of the underlying disease.Clinical Symptoms and Signs
- moderate to severe pain that is uniform around the joint
- Joint effusion
- Muscle spasm
- Decreased range of motion.
Fever in the range of 38.3 to 38.9 degree Celsius (101 to 102 degree F) and sometimes higher is common but may be lacking, especially in persons with rheumatoid arthritis, renal or hepatic insufficiency, or conditions requiring immunosuppressive therapy. The inflamed, swollen joint is usually evident on examination except in the case of a deeply situated joint, such as the hip or the sacroiliac joint.
A focus of extraarticular infection, such as a boil or pneumonia, should be sought. Peripheral blood leukocytosis and a left shift are common findings.
Plain radiographs show evidence of soft tissue swelling, joint space widening, and displacement of tissue planes by the distended capsule. Narrowing of the joint space and bony erosions indicate advanced infection and a poor prognosis. Ultrasound is useful for detecting effusions in the hip, and computed tomography or magnetic resonance imaging can demonstrate infection of the sacroiliac joint and the spine very well.
Laboratory findings
Specimens of peripheral blood and synovial fluid should be obtained before antibiotics are administered. Blood cultures are positive in up to 50 percent of S. aureus infection but are less frequently positive in infection due to other organisms.
The synovial fluid is turbid, serosanguineous(blood mixed), or frankly purulent. Gram-stained smears confirm the presence of large numbers of neutrophils.
The synovial fluid should be examined for crystals, because gout and pseudogout can resemble septic arthritis clinically, and infection and crystal-induced disease occasionally occur together.
Organisms are seen on synovial fluid smears in nearly three-quarters of infections with S. aureus and streptococci and in 30 to 50 percent of infections due to gram-negative and other bacteria. Cultures of synovial fluid are positive in more than 90 percent of cases. Inoculation of synovial fluid into bottles containing liquid media for blood cultures increases the yield of culture.
Treatment
Prompt administration of systemic antibiotics and drainage of the involved joint can prevent destruction of cartilage, postinfectious degenerative arthritis, joint instability, or deformity.
Initial therapy should consist of the intravenous administration of bactericidal agents; direct instillation of antibiotics into the joint is not necessary to achieve adequate levels in synovial fluid and tissue.
An intravenous combination of a third-generation cephalosporin such as cefotaxime (1 g every 8 h) or ceftriaxone (1 to 2 g every 24 h) and either roxacillin or nafcillin (2 g every 4 h) will provide adequate coverage for most infection in adults.
Intravenous vancomycin (1 g every 12 h) should be given if methicillin-resistant S. aureus is a possible pathogen in a hospitalized patient. In addition, an aminoglycoside should be given to intravenous drug users or other patients in whom Pseudomonas aeruginosa may be the responsible agent.
Definitive therapy is based on the identify and antibiotic susceptibility of the bacteria isolated in culture.
Timely drainage of pus and necrotic debris from the infected joint is required for a favorable outcome. Needle aspiration of readily accessible joints such as the knee may be adequate if loculations or particulate matter in the joint does not prevent its through decompression.
Arthroscopic drainage and lavage may be employed initially or within several days if repeated needle aspiration fails to relieve symptoms, decrease the volume of the effusion and the synovial white cell count, and clear bacteria from smears and cultures. In some cases, arthrotomy is necessary to remove loculations and debride infected synovium, cartilage, or bone.
Surgery
Septic arthritis of the hip is best managed with arthrotomy, particularly in young children, in whom infection threatens the viability of the femoral head. Septic joints do not require immobilization except for pain control before symptoms are alleviated by treatment.
Weight bearing should be avoided until signs of inflammation have subsided, but frequent passive motion of the joint is indicated to maintain full mobility.
Popularity: 1% [?]
Related posts:
Join Discussions