Pediatric Hospital Medicine

Chapter 43 • Bone and Joint Infections 261

■ DIAGNOSTIC STUDIES Plain radiography images are typically normal in SA but should be ob tained early in the diagnostic workup to exclude other acute diagnoses such as fractures, Legg-Calve-Perthes disease, slipped capital femoral epiphysis, and bone tumors. 2 For hip pain, Kocher critera can be used to risk stratify the more benign transient synovitis from SA, requiring urgent intervention. Table 43.7 summarizes the five modified Kocher criteria that act as independent risk factors for SA of the hip. Presence of all five criteria indicates a 98% chance of SA, but the scoring has not been validated for other joints. 4 Synovial fluid analyses typical of SA are summarized in Table 43.8. Consider magnetic resonance imaging or a bone scan to diagnose concomitant osteomyelitis if suspected. 2 Kingella kingae is difficult to culture and may be better detected with nasopharyngeal swab, utilization of a blood culture tube for processing of synovial fluid, or detection by polymerase chain reaction. 1 TABLE 43.6 CLINICAL MANIFESTATIONS OF SEPTIC ARTHRITIS Vital signs • Fever • Tachycardia ( ± hypotension) Clinical symptoms • Malaise • Poor appetite • Refusal to move affected joint • Pseudoparalysis Physical examination • Edema, erythema, and tenderness of affected joint • Knee in flexion • Hip flexed, abducted, and externally rotated • Pain with passive range of motion of affected joint Data from Dodwell ER. Osteomyelitis and septic arthritis in children: current concepts. Curr Opin Pediatr . 2013;25:58-63. TABLE 43.7 MODIFIED KOCHER CRITERIA FOR DIAGNOSIS OF SEPTIC ARTHRITIS OF THE HIP Fever > 38.5 °C Non–weight bearing WBC count > 12.0 × 10 6 cells/L

CRP > 2 mg/dL ESR > 40 mm/h

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CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; WBC, white blood cell. Data from Erkilinc M, Gilmore A, Weber M, et al. Current concepts in pediatric septic arthritis. J Am Acad Orthop Surg . 2021;29:196-206.