TABLE 121.2 Initial Antibiotic Therapy: Septic Arthritis a Age Pathogens Antibiotics Neonate 2 mo–5 yrs >5 yrs Adolescent Clindamycin b , c Clindamycin b , c Clindamycin c and ceftriaxone d a Common pathogens and empiric antibiotic coverage by age ceftriaxone for Gram stain without gram-positive cocci, PCR or culture positive for K kingae, or ill appearance c Vancomycin, if high incidence of clindamycin resistance in community or ill appearance, and consider for all hip and shoulder joints d Empiric treatment in sexually active adolescent b Add Clinical Indications for Discharge or Admission The management of septic arthritis consists of hospitalization, parenteral administration of antibiotics ( Table 121.2 ), and joint immobilization Joint irrigation should be performed in selected cases Empiric antibiotic therapy is dictated by the common organisms in the age group, local sensitivities, and by results of the synovial fluid Gram stain Antibiotic administration should be initiated as soon as blood and synovial cultures have been obtained Vancomycin or clindamycin may be indicated depending on the incidence of clindamycinresistant MRSA in the community; vancomycin should also be considered as part of the antimicrobial regimen for critically ill children Gram-negative coverage should be added in neonates and adolescents A third-generation cephalosporin should be added in patients with sickle cell disease because of susceptibility to salmonella infection Surgical intervention for joint irrigation is generally indicated for all cases involving the hip joint; infections in which large amounts of fibrin, debris, or loculations are found within the joint space; or when the patient fails to improve following several days of intravenous antibiotic therapy Open arthrotomy is performed in most cases of pediatric septic arthritis although there is evidence that arthroscopic irrigation or serial needle aspiration may produce equivalent outcomes Expeditious and aggressive management limits but does not eliminate potential sequelae of septic arthritis Lyme Arthritis Lyme disease is a common cause of infectious arthritis in certain geographic locations within the United States The infection is caused by the spirochete Borrelia burgdorferi which is primarily transmitted through the bite of the Ixodes scapularis tick Arthritis is a manifestation of late disease and can occur to 12 months following inoculation Lyme arthritis is most often a monoarticular infection of the knee with the hip being the second most commonly affected joint If left untreated, symptoms can be episodic, lasting several days followed by several weeks to months without symptoms Clinical and laboratory findings are similar to those for septic arthritis Joint swelling is marked and out of proportion to the degree of pain ( Fig 121.4 ) Fever is generally absent, or low grade when present Pain and limitation of movement of the affected joint is less than in septic arthritis, and patients are often able to ambulate despite the swelling Infection can occur without a preceding known history of a tick bite or the classic skin manifestations of erythema migrans Facial palsy or meningitis are more typical of early disseminated disease and therefore are rarely concurrent with arthritis The ESR and CRP are elevated, but less than in septic arthritis When arthrocentesis is performed, the mean leukocyte count in synovial fluid is usually 50,000 to 60,000 cells/mm3 but can exceed 100,000 cells/mm3 with a neutrophil predominance Routine cultures of synovial fluid are negative PCR testing of the synovial fluid may detect B burgdorferi DNA but offers no advantage to serologic testing and is not used routinely for clinical diagnosis In the appropriate clinical setting physical and laboratory findings may be sufficient to identify patients at low risk for septic arthritis and potentially avoid the need for arthrocentesis There is significant overlap in both clinical and laboratory findings which can make it especially difficult to distinguish Lyme arthritis from septic arthritis in the hip Two-tiered diagnostic testing for Lyme arthritis is indicated in endemic areas The first tier should include a serum enzyme-linked immunosorbent assay Positive results should be confirmed by a Western immunoblot for IgG antibodies to B burgdorferi An IgM immunoblot assay is not necessary in late disease and may result in false-positive results Negative serum IgG serology excludes Lyme as the cause of arthritis Treatment for Lyme arthritis consists of a 4-week course of oral antibiotics Doxycycline in a dose of mg/kg/day divided twice daily with a maximum of 100 mg per dose is effective for children older than years, whereas amoxicillin (50 mg/kg/day in three divided doses with a maximum of 1.5 g/day) is sufficient in younger children Cefuroxime (30 mg/kg/day in two divided doses with a maximum of 1,000 mg daily) is an alternative for patients with penicillin allergy Serum antibody titers remain elevated even after adequate antibiotic treatment and should not be used as a measure of success of treatment Persistent or recurrent joint swelling may occur months beyond the initiation of treatment Although this may represent a local autoimmune response, experts recommend retreatment with a second 4week course of oral antibiotics or a 2- to 4-week course of parenteral ceftriaxone FIGURE 121.4 Lyme arthritis of the left knee Transient Synovitis Transient or toxic synovitis is a benign, self-limiting inflammatory condition of the hip It afflicts males more frequently than females and is the most common cause of acute hip pain in children to 10 years of age The underlying cause is unknown, although a postinfectious inflammatory response has been suggested Its presentation can mimic that of septic arthritis of the hip ( Fig 121.5 ), a distinction that is as crucial in management as it is difficult in diagnosis FIGURE 121.5 A seven-year-old child with transient synovitis of the left hip Hip joint is held in same position of comfort as in septic arthritis The onset of symptoms is abrupt with unilateral hip pain and limp Fever is rare, occurring in less than 10% of cases, and when present, is usually low grade Although patients complain of discomfort with movement of the limb, it is generally possible to gently maneuver the hip through a near full range of motion This contrasts with the septic hip in which pain and spasm are more extreme, and patients resist a full range of motion and are often unable to ambulate Additional signs of systemic illness are absent and, despite the label, the child is nontoxic appearing Laboratory tests are generally useful only in attempting to distinguish transient synovitis from more serious conditions The WBC count, ESR, and CRP are generally normal or only slightly elevated The mean WBC count, ESR, and CRP are significantly lower than in septic arthritis; however, sufficient overlap exists between values in transient synovitis and septic arthritis such that they not reliably distinguish between the two conditions in individual patients The Kocher criteria consist of a combination of clinical and laboratory variables which are commonly used as a clinical prediction tool to assist in distinguishing septic arthritis from transient synovitis The original four factors include a history of fever, nonweight bearing, ESR greater than 40 mm/hr, and WBC count greater ... following several days of intravenous antibiotic therapy Open arthrotomy is performed in most cases of pediatric septic arthritis although there is evidence that arthroscopic irrigation or serial needle