Related Experiment Video
Updated: Mar 21, 2026
Knee Arthrocentesis in Adults
Published on: February 25, 2022
Predictive Factors for Differentiating Between Septic Arthritis and Lyme Disease of the Knee in Children
Keith D Baldwin1, Christopher M Brusalis1, Afamefuna M Nduaguba1
1The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.
Insights
Differentiating pediatric knee septic arthritis from Lyme disease is crucial. Key indicators for septic arthritis include pain with motion, fever, elevated C-reactive protein, and young age.
Area of Science:
- Pediatric Orthopedics
- Infectious Diseases
- Rheumatology
Background:
- Distinguishing septic arthritis from Lyme disease in children with knee effusions is clinically challenging.
- Accurate diagnosis is critical for appropriate patient management and treatment.
Purpose of the Study:
- To develop a prediction rule to differentiate septic arthritis from Lyme disease in pediatric patients presenting with knee effusions.
- Identify key clinical and laboratory factors associated with septic arthritis.
Main Methods:
- Retrospective review of 189 pediatric patients (<18 years) with knee effusions undergoing arthrocentesis (2005-2013).
- Inclusion criteria: culture-proven septic arthritis or confirmed Lyme disease via Western blot.
- Exclusion criteria: undiagnosed effusions or cases with both positive culture and Lyme titers.
- Multivariate binary logistic regression analysis to identify independent predictive variables.
Main Results:
- Identified four independent predictors of septic arthritis: pain with short arc motion, history of fever, C-reactive protein >4 mg/L, and age <2 years.
- A risk model demonstrated increasing probability of septic arthritis with the number of predictive factors present (2% with none, 100% with all four).
Conclusions:
- Pain with short arc motion, C-reactive protein >4.0 mg/L, reported fever, and age <2 years are significant predictors of septic arthritis in children.
- The presence of these factors increases the likelihood of septic arthritis, aiding clinical decision-making.
Background:
Differentiating between septic arthritis and Lyme disease of the knee in endemic areas can be challenging and has major implications for patient management. The purpose of this study was to identify a prediction rule to differentiate septic arthritis from Lyme disease in children presenting with knee pain and effusion.
Methods:
We retrospectively reviewed the records of patients younger than 18 years of age with knee effusions who underwent arthrocentesis at our institution from 2005 to 2013. Patients with either septic arthritis (positive joint fluid culture or synovial white blood-cell count of >60,000 white blood cells/mm(3) with negative Lyme titer) or Lyme disease (positive Lyme immunoglobulin G on Western blot analysis) were included. To avoid misclassification bias, undiagnosed knee effusions and joints with both a positive culture and positive Lyme titers were excluded. Historical, clinical, and laboratory data were compared between groups to identify variables for comparison. Binary logistic regression analysis was used to identify independent predictive variables.
Results:
One hundred and eighty-nine patients were studied: 23 with culture-positive septic arthritis, 26 with culture-negative septic arthritis, and 140 with Lyme disease. Multivariate binary logistic regression identified pain with short arc motion, history of fever reported by the patient or a family member, C-reactive protein of >4 mg/L, and age younger than 2 years as independent predictive factors for septic arthritis. A simpler model was developed that showed that the risk of septic arthritis with none of these factors was 2%, with 1 of these factors was 18%, with 2 of these factors was 45%, with 3 of these factors was 84%, or with all 4 of these factors was 100%.
Conclusions:
Although septic arthritis of the knee and Lyme monoarthritis share common features that can make them difficult to distinguish clinically, the presence of pain with short arc motion, C-reactive protein of >4.0 mg/L, patient-reported history of fever, and age younger than 2 years were independent predictive factors of septic arthritis in pediatric patients. The more factors that are present, the higher the risk of having septic arthritis.
Level Of Evidence:
Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.
Related Concept Videos
01:26Factors Affecting the Risk of Infection
The integrity and count of the white blood cells help the body resist pathogens and fight infection. When impaired, it reduces the body's resistance to pathogens. The acidic pH levels of the gastrointestinal, genitourinary tracts, and skin...
01:22Rheumatic Heart Disease II: Clinical Manifestations and Diagnostic Studies