FIGURE 121.3 Five-month-old infant with septic arthritis of the right hip Hip joint is held in flexion, abduction, and external rotation The skin surface should be closely evaluated for local signs of injury Most involved joints will have obvious erythema, warmth, and swelling The exception is the hip joint because of its deep-seated location Swelling may be less obvious in the pudgy infant Fever is a commonly associated sign but is absent in up to one-third of patients Management/Diagnostic Testing The diagnosis of septic arthritis is confirmed by the identification of purulent fluid within the joint space Arthrocentesis is a mandatory procedure in all suspected causes of septic arthritis The decision to perform this procedure is based on the degree of clinical suspicion in combination with results of laboratory tests and imaging studies; none of these in isolation are 100% sensitive in detecting or excluding septic arthritis from other conditions A sample of synovial fluid is often the only means of discriminating septic arthritis from less serious inflammatory processes The mean peripheral WBC count is generally elevated in children with septic arthritis, however, more than half of the patients will have a WBC count less than 15,000/mm3 The ESR and CRP are more sensitive markers and are elevated in