Evidence Based Strategies: First Steps of Identifying Musculoskeletal Infections in Children

Column Author:   Bahar Barani, MD | Chief Resident  

Column Editor: Kathleen J. Berg, MD, FAAP | Medical Director, Office of Evidence-Based Practice, Associate Professor of Pediatrics, University of Missouri-Kansas City School of Medicine; Clinical Assistant Professor of Pediatrics, University of Kansas School of Medicine

Musculoskeletal (MSK) infection is a major cause of morbidity in the pediatric population and often requires hospitalization and prolonged antibiotic use. The annual incidence of MSK infection-related hospitalization is five to 10 cases per 100,000 children.¹ Diagnoses affecting children in this category include osteomyelitis, septic arthritis, and pyomyositis. Osteomyelitis and septic arthritis in pediatric populations often occur due to hematogenous spread of the causative organism. The most common organism is Staphylococcus aureus in all age groups. Often, children with methicillin-resistant S. aureus are more ill-appearing and have more pronounced fever than those with methicillin-sensitive S. aureus. Kingella kingae, more commonly seen in infants and preschool-aged children, can have more insidious onset. Early diagnosis is important in preventing further spread, sepsis and complications such as growth plate disturbances.²

Several barriers exist to timely diagnosis of MSK infection. These barriers include insidious symptoms that often overlap with other less serious diagnoses such as cellulitis. In addition, no single laboratory test or first-line imaging modality reliably solidifies the diagnosis. Different models of risk stratification currently provide guidance on workup and management of MSK infection.^1,2

When a child presents with limp and/or extremity pain, providers must determine the risk of MSK infection. The “Kocher Criteria” are familiar to pediatric providers as a means of identifying risk for septic arthritis of the hip. These criteria consider non-weight bearing status, temperature greater than 38.5 degrees Celsius, erythrocyte sedimentation rate (ESR) greater than 40 mm/hr, and white blood cell (WBC) count greater than 12,000 cells/mm³.^3,4 With the availability of additional biomarkers, Caide et al. added C-reactive protein (CRP) greater than 2 mg/dL to these criteria.⁵ It is important to note, however, that the criteria are not applicable to joints other than the hip.^6,7 Additionally, the “Kocher Criteria” are not a surrogate tool for assessing risk of osteomyelitis.⁸   

Recently published in Pediatrics, Stephan et al. identified 10 best predictors for acute hematogenous osteomyelitis (AHO). Using these 10 predictors, the authors developed a new 4-point risk score that can guide clinical decision-making in relation to the risk for osteomyelitis. This novel risk score gives one point for each of the following: duration of illness more than three days, history of fever or highest emergency department temperature greater than or equal to 38 degrees Celsius, CRP greater than 2 mg/dL, and ESR greater than 25 mm/hr. When assigning a score of 3 or higher as high risk for AHO and < 3 as low risk for AHO, the tool correctly classified 85% of patients with a sensitivity of 0.78 (95% CI: 0.75-0.88) and specificity of 0.86 (95% CI: 0.85-0.88).⁹ This new tool can help clinicians make decisions about workup for insidious symptoms that may be due to osteomyelitis.

In January 2024, the Pediatric Infectious Diseases Society (PIDS) and the Infectious Diseases Society of America (IDSA) published updated guidelines for diagnosing and managing acute bacterial arthritis in the pediatric population. Pertinent updates for the evaluation of acute bacterial arthritis include the recommendation to obtain a CRP and recommendation against ordering procalcitonin. Blood culture should be obtained prior to initiation of antibiotic if patient stability and resources allow. Although plain radiography has poor sensitivity for joint effusion or osteomyelitis, it should still be obtained initially to evaluate for other etiologies of acute musculoskeletal pain. When further imaging is required, ultrasound can help identify an effusion; subsequently, magnetic resonance imaging is the study of choice. Empiric antimicrobial therapy should cover S. aureus, with the decision to cover for methicillin resistance based on local susceptibility patterns and severity of presentation. In addition, for children aged 6 to 48 months, empiric coverage for K. kingae should be included. Consideration of vaccine status and other exposures may guide choice of antibiotic as well.¹⁰

Given its non-specific nature, clinicians should have high index of suspicion for MSK infection when diagnosing children with complaints that involve the musculoskeletal system. Newer prediction models are available that can guide clinicians in making a diagnosis of osteomyelitis. Similarly, the new clinical practice guideline by the PIDS and IDSA can provide helpful information about the utility of various diagnostic tests, about an order to obtain these tests, and about initial antibiotic management for children with suspected septic arthritis. Orthopedic Surgery and Infectious Diseases provide expert guidance throughout the diagnostic and therapeutic process. Early consultation with these specialties expedites care and improves outcomes for your patient.

References:

1. Dolitsky R, DePaola K, Fernicola J, Collins C. Pediatric musculoskeletal infections. Pediatr Clin North Am. 2020;67(1):59-69. doi:10.1016/j.pcl.2019.09.001
2. Hester GZ, Nickel AJ, Watson D, Swanson G, Laine JC, Bergmann KR. Improving care and outcomes for pediatric musculoskeletal infections. Pediatrics. 2021;147(2):e20200118. doi:10.1542/peds.2020-0118
3. Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999;81(12):1662-1670. doi:10.2106/00004623-199912000-00002
4. Kocher MS, Mandiga R, Murphy JM, et al. A clinical practice guideline for treatment of septic arthritis in children: efficacy in improving process of care and effect on outcome of septic arthritis of the hip. J Bone Joint Surg Am. 2003;85(6):994-999.
5. Caird MS, Flynn JM, Leung YL, Millman JE, D’Italia JG, Dormans JP. Factors distinguishing septic arthritis from transient synovitis of the hip in children. A prospective study. J Bone Joint Surg Am. 2006;88(6):1251-1257. doi:10.2106/JBJS.E.00216
6. Obey MR, Minaie A, Schipper JA, Hosseinzadeh P. Pediatric septic arthritis of the knee: predictors of septic hip do not apply. J Pediatr Orthop. 2019;39(10):e769-e772. doi:10.1097/BPO.0000000000001377
7. Bisht RU, Burns JD, Smith CL, Kang P, Shrader MW, Belthur MV. The modified Kocher criteria for septic hip: Does it apply to the knee? J Child Orthop. 2022;16(3):233-237. doi:10.1177/18632521221106383
8. Nguyen A, Kan JH, Bisset G, Rosenfeld S. Kocher criteria revisited in the era of MRI: how often does the Kocher criteria identify underlying osteomyelitis? J Pediatr Orthop. 2017;37(2):e114-e119. doi:10.1097/BPO.0000000000000602
9. Stephan AM, Platt S, Levine DA, et al. A novel risk score to guide the evaluation of acute hematogenous osteomyelitis in children. Pediatrics. 2024;153(2):e2023063153. doi:10.1542/peds.2023-063153
10. Woods CR, Bradley JS, Chatterjee A, et al. Clinical practice guideline by the Pediatric Infectious Diseases Society (PIDS) and the Infectious Diseases Society of America (IDSA): 2023 Guideline on Diagnosis and Management of Acute Bacterial Arthritis in Pediatrics. J Pediatric Infect Dis Soc. 2024;13(1):1-59. doi:10.1093/jpids/piad089