Septic Arthritis - Causes, Symptoms and Treatments
A medical emergency, septic (infectious) arthritis is caused by bacterial invasion of a joint, resulting in inflammation of the synovial lining. If the microbes enter the joint cavity, effusion and pyogenesis follow, with eventual destruction of bone and cartilage.
Septic arthritis can lead to ankylosis and even fatal septicemia. However, prompt antibiotic therapy and joint aspiration or drainage cures most patients.
Causes of Septic Arthritis:
In most cases of septic arthritis, bacteria spread from a primary site of infection, usually in adjacent bone or soft tissue, through the bloodstream to the joint.
Common infecting microbes include four strains of gram-positive cocci Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, and Streptococcus viridans-and two strains of gram-negative cocci - Neisseria gonorrhoeae and Haemophilus influenzae. Various gram-negative bacilli - Escherichia coli, Salmonella, and Pseudomonas, for example-also cause infection.
Anaerobic microbes such as grampositive cocci usually infect adults and children over age 2. H. influenzae most often infects children under age 2.
Various factors can predispose a person to septic arthritis. Any concurrent bacterial infection (of the genitourinary or the upper respiratory tract, for example) or serious chronic illness (such as cancer, renal failure, rheumatoid arthritis, systemic lupus erythematosus, diabetes, or cirrhosis) heightens susceptibility. Consequently, alcoholics and elderly people run a higher risk of developing septic arthritis.
Of course, susceptibility increases with diseases that depress the autoimmune system or with prior immunosuppressive therapy. I.V. drug abuse (by heroin addicts, for example) can also cause septic arthritis.
Other predisposing factors include recent articular trauma, joint surgery, intraarticular injections, and local joint abnormalities.
Signs and symptoms of Septic Arthritis:
Acute septic arthritis begins abruptly, causing intense pain, inflammation, and swelling of the affected joint, with lowgrade fever. It usually affects a single joint. It most often develops in the large joints but can strike any joint, including the spine and small peripheral joints.
Systemic signs of inflammation may not appear in some patients. Migrratory polyarthritis sometimes precedes laocalization of the infection. If the bacteria invade the hip, pain may occur in the groin, upper thigh, or buttock, or may be referred to the knee.
Diagnosis of Septic Arthritis:
Two sets of positive culture and Gram stain smears of skin exudates, sputum, urethral discharge, stools, urine, or nasopharyngeal smear confirm septic arthritis. Joint fluid analysis shows gross pus or watery, cloudy fluid of decreased viscosity, usually with 50,000/ul or more white blood cells (WBCs), primarily neutrophils.
When synovial fluid culture is negative, a positive blood culture may confirm the diagnosis. Synovial fluid glucose is often low compared with a simultaneous 6-hour postprandial blood glucose test.
Other diagnostic measures include the following:
1. X-rays can show typical changes as early as 1 week after initial infection - distention of joint capsules, for example, followed by narrowing of joint space (indicating cartilage damage) and erosions of bone (joint destruction).
2. Radioisotope joint scan for less accessible joints (such as spinal articulations) may help detect infection or inflammation but isn't itself diagnostic.
3. C-reactive protein may be elevated, as well as WEC count, with many polymorphonuclear cells; erythrocyte sedimentation rate is increased.
4. Lactic assay can distinguish septic from nonseptic arthritis.
Treatment of Septic Arthritis:
Antibiotic therapy should begin promptly; it may be modified when sensitivity results become available. Penicillin G is effective against infections caused by S. aureus, S. pyogenes, S. pneumoniae, S. viridans, and N. gonorrhoeae. A penicillinase-resistant penicillin, such as nafcillin, is recommended for penicillin G-resistant strains of S. aureus; ampicillin, for H. influenzae; gentamicin, for gramnegative bacilli.
Medication selection requires drug sensitivity studies of the infecting organism. Bioassays or bactericidal assays of synovial fluid and bioassays of blood may confirm clearing of the infection.
Treatment of septic arthritis requires monitoring of progress through frequent analysis of joint fluid cultures, synovial fluid WEC counts, and glucose determinations.
Codeine or propoxyphene can be given for pain if needed. (Aspirin causes a misleading reduction in swelling, hindering accurate monitoring of progress.) The affected joint can be immobilized with a splint or traction until movement can be tolerated.
Needle aspiration (arthrocentesis) to remove grossly purulent joint fluid should be repeated daily until fluid appears normal. If excessive fluid is aspirated or the WBC count remains elevated, open surgical drainage (usually arthrotomy with lavage of the joint) may be necessary for resistant infection or chronic septic arthritis.
Late reconstructive surgery is warranted only for severe joint damage and only after all signs of active infection have disappeared, which usually takes several months. In some cases, the recommended procedure may be arthroplasty or joint fusion.
Prosthetic replacement remains controversial; it may exacerbate the infection. However, it has helped patients with damaged femoral heads or acetabula.
Special considerations of Septic Arthritis:
1. Practice strict aseptic technique with all procedures. Prevent contact between immunosuppressed patients and infected patients.
2. Watch for signs of joint inflammation: heat, redness, swelling, pain, or drainage. Monitor vital signs and fever pattern. Remember that corticosteroids mask signs of infection.
3. Check splints or traction regularly. Keep the joint in proper alignment, but avoid prolonged immobilization. Start passive range-of-motion exercises immediately, and progress to active exercises as soon as the patient can move the affected joint and put weight on it.
4. Monitor pain levels and medicate accordingly, especially before exercise (remember that the pain of septic arthritis is easy to underestimate). Administer analgesics and narcotics for acute pain and heat or ice packs for moderate pain.
5. Carefully evaluate the patient's condition after joint aspiration. provide emotional support throughout the diagnostic tests and procedures, which should be previously explained to the patient. Warn the patient before the first aspiration that it will be extremely painful.
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