Facebook Twitter YouTube



Predicting the Presence of Adjacent Musculoskeletal Infections In Septic Arthritis

Saturday, October 20, 2012: 10:22 AM
Melrose (Hilton Riverside)
Shiva Daram, John Dawson and Scott Rosenfeld, Orthopedic Surgery, Baylor College of Medicine, Houston, TX

Purpose: The gold standard for treatment of septic arthritis is urgent surgical debridement.  Recent studies have shown that adjacent infections such as osteomyelitis, subperiosteal abscess, and intramuscular abscess frequently occur with septic arthritis.  If these adjacent infections are not initially recognized, initial treatment may be inadequate and multiple procedures may be required.  The purpose of this study is to develop a prediction algorithm to distinguish septic arthritis with adjacent infections from isolated septic arthritis. 

Methods: We performed a retrospective review of 87 children treated for septic arthritis.  All patients underwent MRI.  51 patients had adjacent infections, and 36 patients had isolated septic arthritis. Septic arthritis was confirmed by joint fluid aspiration showing positive cultures, WBC>50,000, or organisms on gram stain.  Sixteen variables (age, gender, temperature, WBC, CRP, ESR, ANC, hematocrit, platelet count, heart rate, systolic blood pressure, diastolic blood pressure, symptom duration, weight bearing status, prior antibiotic therapy, and prior hospitalization) were reviewed. Infants less than one year old and patients with incomplete data were excluded.  Variables were compared using univariate and multivariate regression analysis to identify independent predictors of adjacent infections.  Optimal cutoff values were determined for each variable and a prediction algorithm for differentiating between adjacent infections and isolated septic arthritis was created.

Results: Five significant independent multivariate predictors were identified: age>4 years, CRP>8.9, duration of symptoms>3 days, platelet count <310, and ANC>7.2.

Table 1: Cutoff Values for Predictors (p<.05) of Adjacent Infectio

Predictor

Optimal Cutoff Value

Odds Ratio

Age (y)

4

7.3

CRP (mg/L)

8.9

6.6

Duration of Symptoms (d)

3

5.4

Platelet Count (x106 cells/mL)*

310

3.8

ANC (x106 cells/mL)

7.2

3.3

Table 2: Probability of Adjacent Infection Based on Number of Predictors

Number of factors

Positive Adjacent Infection (n)

Total in population

Sensitivity

Specificity

Correctly Classified

0

25% (1)

4

100%

0%

58%

1

14% (1)

7

98%

8%

61%

2

17% (3)

18

96%

25%

67%

3

55% (12)

22

90%

67%

80%

4

89% (17)

19

67%

94%

78%

5

100% (17)

17

33%

100%

60%

Conclusion: Age, CRP, duration of symptoms, platelet count, and ANC were predictive of adjacent infections.  As a patient with septic arthritis has more positive factors, the likelihood of an adjacent infection increases.   Patients with 3 or more positive predictors should undergo preoperative MRI in their workup of septic arthritis to evaluate for adjacent infections. Those with less factors may forgo preoperative MRIs, but must still be followed closely for signs of continued infection after surgical treatment of septic arthritis.