Three Part Question
In [children presenting with acute hip pain], is there [a single clinical or laboratory test] that will [distinguish between septic arthritis and
A 3 year old boy presents to paediatric A&E with refusal to weightbear for the last day and a temperature of 37.9 ° centigrade. The pain is located in his hip. What clinical or laboratory tests could help discriminate between septic arthritis and transient synovitis?
Medline 1991-2007, using the PubMed interface
Search: Septic arthritis AND hip (129 papers)
Septic arthritis AND transient synovitis (21 papers)Septic AND reactive AND arthritis AND hip (10 papers)
Cochrane library and BMJ's Clinical Evidence for the
search terms "transient synovitis", "reactive arthritis" and "septic arthritis" 0 relevant
Limits: all child 0-18, published in the last 10 years, English
5 papers were relevant
|Author, date and country
||Study type (level of evidence)
|Kocher et al,|
|168 children who underwent hip aspiration for evaluation of acute hip pain (82 children with septic arthritis, 86 with transient synovitis)||Level II (diagnostic study)||Probability algorithm for differentiating SA and TrS on basis of independent predictors:|
1. Fever >38.5°C
2. Non weight-bearing
3. ESR>40 mm/hr
4. Serum WCC >12 x 10 to the power of 9
|Individual variables alone not able to distinguish between SA and TrS|
Probability of SA with number of predictors present:
0 - <0.2%
1 - 3.0%
3 - 40.0%
4 - 93.1%
5 - 99.6%
|Caird et al,|
|48 children age7mo-16 yrs who underwent hip aspiration because of suspected SA||Level I (Validation/diagnostic study)||Predictors:|
1. Temp >38.5 °C
2. sWCC >12 x 10 to the power of 9
3. ESR >40 mm/hr
4. CRP >20 mg/L
5. Refusal to weight bear
|Probability of SA with number of predictors present:|
0 - 16.9%
1 - 36.7%
2 - 62.4%
3 - 82.6%
4 - 93.1%
5 - 97.5%
On backward elimination CRP was the only variable to influence the outcome SA significantly
|Small sample: lacks power|
|Kocher et al,|
|154 children who underwent hip aspiration for evaluation of acute hip pain (51 with SA, 103 with TrS)||Level I (Validation study)||Probability algorithm on basis of independent predictors:|
1. Fever >38.5 °C
3. ESR >40 mm/hr
4. sWCC >12 x 10 to the power of 9
|Probability of SA with number of predictors present:|
0 - 2%
1 - 9.5%
2 - 35%
3 - 73%
4 - 93%
|Luhmann et al,|
|163 patients who underwent hip aspiration for evaluation of acute hip pain (47 with SA, 118 with TrS)||Level I (Validation/diagnostic study)||Predictors:|
1. History of fever >38.5°C
3. Duration of symptoms
4. Refusal to weightbear
5. Recent antibiotic use
6. Temperature on admission
8. sWCC + diff
9. Prior health care visit
|Predicted probability of SA when Kocher's variables all present: 59%|
Three-variable model of history of fever, serumWCC and prior health care visit gave predicted probability of 71%
|Retrospective; small SA sample, lacks power
No CRP; high percentage of TrS suggests low threshold for hip aspiration|
|Jung et al,|
|127 children with acute hip pain (27 with SA, 97 with TrS)||Level III (diagnostic study)||Predictors:|
1. Temp > 37°C
4. ESR >20 mm/hr
5. CRP >10 mg/L
|Predictors 1,2,3,4,5 all p<0.001, but lack of obvious cut-off point limits usefulness|
Predicted probability of SA when 1,2,4,5 all present is 98.8%
|Small SA sample
Complicated algorithm, not practical for clinical use
High number of TrS cases suggests low threshold for hip aspiration|
Distinguishing between septic arthritis and transient synovitis of the hip joint in the limping child can be a difficult clinical undertaking but is vital. The two conditions can present with similar symptoms and clinical features but the treatment and potential for negative sequelae are significantly different. Whereas transient synovitis runs a benign self-limiting course that can be managed with observation and NSAIDS, septic arthritis needs urgent diagnosis, operative irrigation and antibiotics. Poor outcomes are associated with diagnostic delays, and negative
sequelae include osteonecrosis of the femoral head, growth arrest and sepsis (Fabry, Lunseth).
There is much debate amongst clinicians over how best to accurately and quickly distinguish septic arthritis from transient synovitis with no one pathognomonic symptom, clinical feature, blood test or investigation confirming the diagnosis. If there is sufficient clinical suspicion of septic arthritis, the hip joint must be aspirated under image guidance (ultrasound or fluoroscopy) and the fluid sent for laboratory examination. Joint aspiration is considered the gold standard test
but is an invasive and unpleasant procedure, particularly for a child, usually requiring general anaesthesia. The question is, ‘‘what amounts to
sufficient clinical suspicion?’’. How much weight should be attached to each clinical finding or investigation result? There is therefore a need for a clinical prediction rule (CPR) to aid the clinician to safely distinguish between the two diagnoses and avoid both delayed treatment and
Kocher’s (1999) clinical prediction model to differentiate between septic arthritis and transient synovitis forms the basis of subsequent validation studies by Luhmann (2004), Caird (2006) and Kocher (2004).Kocher (2004) prospectively evaluated 154 patients and found that the same four variables were still most likely to predict the outcome of septic arthritis, with a diminished, but nevertheless good, diagnostic performance in the new patient population (93% probability with all four predictors present).
Luhmann et al, in another tertiary children’s hospital, applied the same proposed CPR retrospectively on all children who had undergone aspiration of the hip joint as part of their work-up for acute hip pain. Despite similar patient demographics, they found a lower predicted probability of septic arthritis (59%) when all four variables were present. These findings emphasise the value of validating all clinical prediction rules prior to application in clinical practice. Caird et al published a validation study of Kocher’s CPR, including 48 children presenting with signs and symptoms suspicious enough to warrant ultrasound-guided
hip aspiration. The findings supported Kocher’s model to a certain extent: the likelihood of a patient having septic arthritis increased with the number of positive factors; however, the predicted
probability of septic arthritis with none of the predictors present was still 16.9%. The retrospective derivation study by Jung et al included 97 patients with transient synovitis and 27 with septic arthritis. There are two main issues with their methodology. Firstly, not all patients included in the study underwent the golden standard investigation. Secondly, only patients with a positive synovial culture were definitely diagnosed with septic arthritis, oddly leaving joints with a positive microscopy (ie, synovial aspirate white cell count .50 000 ml21)but negative culture possibly classified as transient synovitis. Finally, Jung’s rule has not been externally validated.
In summary, Kocher’s (1999) proposed four predictor clinical decision rule remains the most useful clinical tool to date despite inadequate external validation. CRP measurement may have an additional benefit as suggested by Caird et al. The study by Jung et al has sufficient methodological flaws as to limit its usefulness.
SA = septic arthritis ; TrS = transient synovitis ; sWCC = serum white cell count; diff = white cell count differential; CRP = C-reactive protein ; ESR = erythrocyte sedimentation rate ; ROC = receiver operating characteristics
Clinical Bottom Line
There is no one investigation or blood test
that can distinguish between septic arthritis and transient synovitis. (Grade B)
There is no clinical prediction rule that has been validated by multi-centre prospective studies involving large patient numbers. (Grade B)
The combined presence of fever, nonweight bearing, C-reactive protein >20 or erythrocyte sedimentation rate >40, and a white cell count >12 is suspicious of septic arthritis. (Grade B)
- Kocher MS, Zurakowski D, Kasser JR Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm Journal of Bone and Joint Surgery J Bone Joint Surg Am. 1999 Dec;81(12):1662-70.
- 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 Jun;88(6):1251-7.
- Kocher MS, Mandiga R, Zurakowski D, Barnewolt C, Kasser JR. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am. 2004 Aug;86-A(8):1629-35.
- Luhmann SJ, Jones A, Schootman M, Gordon JE, Schoenecker PL, Luhmann JD. Differentiation between septic arthritis and transient synovitis of the hip in children with clinical prediction algorithms. J Bone Joint Surg Am. 2004 May;86-A(5):956-62.
- Jung ST, Rowe SM, Moon ES, Song EK, Yoon TR, Seo HY. Significance of laboratory and radiologic findings for differentiating between septic arthritis and transient synovitis of the hip. J Pediatr Orthop. 2003 May-Jun;23(3):368-72.
- Fabry G, Meire E. Septic arthritis of the hip in children: poor results after late and inadequate treatment. J Pediatr Orthop 1983;3:461–6.
- Lunseth PA, Heiple KG. Prognosis in septic arthritis of the hip in children. Clin Orthop Relat Res 1979;139:81–5.