Septic arthritis is a joint inflammation due to an infection usually involving synovial joints. Many agents may cause septic arthritis in children, but the vast majority are due to various strains of Staphylococcus and Streptococcus and Kingella kingae. Septic arthritis can cause severe deformity and disability, especially when involving the hip. The joint is damaged by enzymes produced by the bacteria and leukocytes, causing protoglycan loss and collagen degradation. Inflammation may cause secondary vascular damage from thrombosis or direct compression of vessels.
Unlike osteomyelitis, which may resolve without treatment, septic arthritis causes joint damage. This makes septic arthritis a more serious disease than osteomyelitis.
Clinical features are age related.
Neonate with septic arthritis may show few clinical signs. The most consistent finding is a loss of spontaneous movement of the extremity and posturing of the joint at rest. The hip is positioned in flexion, abduction, and some lateral rotation. Fever is often absent, and the neonate may not appear ill.
Infant and child septic arthritis produces local and systemic signs of inflammation. The joint is swollen and tender, and the child resists movement. Hip infections result in severe limitation of rotation, a useful sign in separating septic arthritis from osteomyelitis. Radiographs early in the disease may be deceptive. A negative study is not significant. Widening of the joint is significant. Ultasound studies may show joint effusions. Bone scans show slight to moderate increased uptake over the joint.
The most useful laboratory studies are the sedimentation rate and CRP. The ESR is usually elevated above 25 mm/hour. This test is not reliable for diagnosis in the neonate.
The diagnosis of septic arthritis in children is established by joint aspiration. This evaluation should be performed early and not delayed to obtain a bone scan or other imaging studies. Joint fluid in septic arthritis is cloudy, with leukocyte counts above 50,000 and PMNs predominating. Perform a Gram stain and culture. Cultures will be negative in 20–30% of cases of septic arthritis and thus a negative study does not rule out a joint infection. Culture the blood before starting antibiotic treatment.
Differential diagnosis includes poststreptococcal reactive arthritis, rheumatoid arthritis, and toxic synovitis. Differentiate toxic synovitis by considering four signs. If three or four of these signs are present, the diagnosis is >90% likely to be septic arthritis rather than toxic synovitis.
Treatment of Septic Arthritis in Children
Manage with antibiotics and drainage.
Antibiotic treatment Start with an agent that is statistically most likely to be effective. Later, the antibiotics may be changed based on the culture reports. Parenteral treatment is continued for several days and the clinical course monitored. Failure to improve suggests that the antibiotic is ineffective or that the drainage is incomplete. The duration of parenteral antibiotics should be based on the rapidity of clinical response in reduction of fever, local inflammation, and CRP response. Arbitrary rigid regimens prolong hospitalization and increase costs and patient discomfort without improving results. Most septic arthritis in chilldren may be managed with parenteral antibiotics for 3 to 21 days followed by antibiotics for a total of about four weeks.
Joint drainage is necessary for all cases and should be done promptly.
Serial needle aspiration is a traditional method of drainage. Aspirate initially and as necessary to keep the joint free of pus. Most joints should be drained several times. If response to needle aspiration is slow, consider open or arthroscopic drainage.
Open drainage is mandatory for the hip. Consider open drainage for other joints if the diagnosis is delayed or if the situation is complicated.
Arthroscopic drainage is an option for large joints in children. Place a drain.
Immobilization in septic arthritis is unnecessary. Avoid placing the child in traction, as the child will naturally hold the limb in the position of greatest comfort, which is the position in which intraarticular pressure is least.
Knee Residual deformity is most likely if the infection occurs in infancy and treatment is delayed. Usually a valgus or varus deformity develops due to displacement or loss of the physis. The deformity is permanent and often progressive.
Hip Ischemic changes in the hip are common and varied, including absence of or delayed ossification, loss and then return of ossification, or most severe complete loss or collapse. In this most severe form, increasing deformity may be present. Deformity varies, depending upon the extent of articular and physeal cartilagenous damage.