The use of CRP within a clinical prediction algorithm for the differentiation of septic arthritis and transient synovitis in children
R. Singhal, D. C. Perry, F. N. Khan, D. Cohen, H. L. Stevenson, L. A. James, J. S. Sampath, C. E. Bruce
From Alder Hey Children’s Hospital, Liverpool, United Kingdom
Clinical prediction algorithms are used to differentiate transientsynovitis from septic arthritis. These algorithms typically include the erythrocyte sedimentation rate (ESR), although in clinical practice measurement of the C-reactive protein (CRP) has largely replaced the ESR. We evaluated the use of CRP in a predictive algorithm. The records of 311 children with an effusion of the hip, which was confirmed on ultrasound, were reviewed (mean age 5.3 years (0.2to 15.1)). Of these, 269 resolved without intervention and without long-term sequelae and were considered to have had transient synovitis. The remaining 42 underwent arthrotomy because of suspicion of septic arthritis. Infection was confirmed in 29 (18 had micro-organisms isolated and 11 had a high synovial fluid white cell count). In the remaining 13 no evidence of infection was found and theywere also considered to have had transient synovitis. In total 29 hips were categorised as septic arthritis and 282 as transient synovitis. The temperature, weight-bearing status, peripheral white blood cell count and CRP was reviewed in each patient. A CRP > 20 mg/l was the strongest independent risk factor for septic arthritis (odds ratio 81.9, p < 0.001). A multivariable prediction model revealedthat only two determinants (weight-bearing status and CRP > 20 mg/l) were independent in differentiating septic arthritis from transient synovitis. Individuals with neither predictor had a < 1% probability of septic arthritis, but those with both had a 74% probability of septic arthritis. A two-variable algorithm can therefore quantify the risk of septic arthritis, and is an excellent negativepredictor.
R. Singhal, MBBS, MS (Ortho), MRCSEd, Registrar D. C. Perry, MB, ChB (Hons), MRCS (Eng), Registrar, PhD Student F N. Khan, MBBS, MRCSEd, . Specialty Trainee D. Cohen, MBChB, FRCS (Tr & Orth), Registrar H. L. Stevenson, MBCh, FRCS (Tr & Orth), Registrar L. A. James, MBBS, FRCSEd (Tr & Orth), Consultant Orthopaedic Surgeon C. E. Bruce, MBChB, FRCS (Tr & Orth), ConsultantOrthopaedic Surgeon Alder Hey Children’s Hospital, Department of Orthopaedic Surgery, Eaton Road, West Derby, Liverpool L12 2AP, UK. J. S. Sampath, MBBS, MSc, FRCSEd (Tr & Orth), Consultant Orthopaedic Surgeon SPARSH Hospital, Department of Orthopaedics, The Health City, Bommasandra Industrial Area, Hosur Road, Bangalore 560099, India. Correspondence should be sent to Mr R. Singhal; e-mail:email@example.com ©2011 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.93B11. 26857 $2.00 J Bone Joint Surg Br 2011;93-B:1556–61. Received 3 February 2011; Accepted after revision 15 July 2011
Several algorithms have been proposed to assist in differentiating between septic arthritis and transient synovitis of the hip in children.1-6 This distinction is crucial asthe natural history, and hence treatment, of the two diseases differs greatly. Whilst transient synovitis is a benign condition with little potential for long-term serious damage, septic arthritis can lead to a poor outcome, particularly if the treatment is delayed.7 Kocher, Zurakowski and Kasser1 initially described several variables to aid in the differentiation of these conditions: temperature >38.5°C, inability to weight-bear, erythrocyte sedimentation rate (ESR) > 40 mm/hr and peripheral white blood cell count > 12 000 cells/mm3. However, in these conditions ESR has largely been replaced by estimation of the C-Reactive Protein (CRP).8 CRP is an acute phase reactant, which has a more rapid response to disease than ESR. It is influenced less by external factors and its measurement...