Background

Establishing the diagnosis in a child presenting with an atraumatic limp can be challenging. There is particular difficulty distinguishing septic arthritis (SA) from transient synovitis (TS) and consequently clinical prediction algorithms have been devised to differentiate the conditions using the presence of fever, raised erythrocyte sedimentation rate (ESR), raised white cell count (WCC) and inability to weight bear. Within Europe measurement of the ESR has largely been replaced with assessment of C-reactive protein (CRP) as an acute phase protein. We have evaluated the utility of including CRP in a clinical prediction algorithm to distinguish TS from SA.

Clinical prediction algorithms are used to differentiate transient synovitis 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 (0.2 to 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 they were 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 revealed that 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 negative predictor.

Introduction: Evaluation of acute hip pain in children can be challenging, because there are several diagnoses to consider. Most patients have a transient synovitis of the hip, which is a benign and self-limited condition. However, its similarities with other more serious disease make the diagnosis one of exclusion. In the Children’s Hospital of Geneva, children presenting with an acute hip pain are treated according to a specific screening protocol including blood sample with rheumatoid panel, hip ultrasound, and conventional X-rays. The objective of our study were to assess the efficacy of the screening protocol on the final diagnosis. We also provided a better characterization of transient synovitis of the hip.

Methods: We retrospectively reviewed the medical records of children who had the investigation’s protocol between 1999 and 2003.

Results: 269 medical records were reviewed comprising 66.2% of boys and 33.8% of girls, with a mean age of 5.5 years. Prior to presentation, 68.4% of children reported pain of < 24 hours in duration. Limp or refusal to bear weight was observed in all cases. According to the Kocher’s predictors of septic arthritis of the hip (fever, non weight-bearing, ESR > 40 mm/h, serum WBC count of > 12000 cells/mm3), 62% had zero predictor, 22% had one, 15% two, 1% three, and none four. A positive rheumatoid factor test was found in 18% of children, whereas 16% of patients had a positive antinuclear antibody test. During hospitalisation one child was diagnosed as having septic arthritis. The remaining patients were diagnosed by exclusion as having a transient synovitis of the hip since clinical follow-up was normal at 6 weeks.

Conclusion: Transient synovitis of the hip is a diagnosis of exclusion, and septic arthritis is the main condition to rule out. Using Kocher’s predictors of septic arthritis is useful for distinction between both conditions early at presentation. In our collective, only 3 patients with transient synovitis had a three of four predictors. Our study also showed that screening for a rheumatologic disease should not be done routinely at the first episode of hip pain. Indeed, positive tests were never confirmed with a clinical situation evocative of rheumatologic disease. More selective criteria should be used before doing a rheumatologic panel. Furthermore our work emphasizes the economical impact of a management of this frequent condition with less blood investigations.

Background: Distinguishing septic arthritis from transient synovitis of the hip in children can be both crucial and challenging. In 1999, Kocher et al suggested four clinical predictors, fever > 38.5°C, inability to weight bear, WBC count > 12.0x109/L, and ESR> 40mm/hr; that, when combined were highly predictive of septic arthritis in children (99.6%). This figure was challenged by Luhmann et al, stating that the clinical prediction did not exceed 59%. In 2006, Caird et al recommended adding CRP of > 20mg/L as a fifth predictor.

Aims: To assess the value and accuracy of clinical prediction algorithms in distinguishing septic arthritis from transient synovitis of the hip in children in our hospital.

Methods: A retrospective review of all children admitted to our institution with painful hips was carried out over a period of four years (Feb 2003 to Mar 2007). One-hundred and twenty-two admissions (115 patients, 7 re-admissions) were reviewed.

Results: 79 patients (64.8%) were males. The mean age was 6 years (9 months to 15 years).

86 patients (70.5%) were diagnosed with transient synovitis. All the 7 re-admissions were from this group. Only one of the re-admissions was diagnosed with confirmed septic arthritis.

4 patients (3.3%) were diagnosed with definite septic arthritis with positive cultures from the hip, and 1 (0.8%) with probable septic arthritis (negative culture).

The presence of the clinical predictors was compared between the transient synovitis and septic arthritis groups, using Fisher’s exact test. Only the raised temperature and CRP were found to be significantly different (p< 0.05).

Only two children (40%) with confirmed septic arthritis had four or more predictors (one had all five, and the other was able to partially weight bear). The third child had a raised temperature and CRP, and the fourth had a raised temperature only. The fifth patient (20%) was diagnosed with probable septic arthritis. His cultures were negative, but he was already on intravenous antibiotics. This patient did not have any of the predictors on admission (temperature was 38.3°C, CRP 10.7). However, he spiked a temperature of 40°C 24 hours post admission despite being on antibiotics, and his CRP increased to 34.5mg/L.

In the transient synovitis group, two patients (2.2%) had positive five predictors, but were proven to have transient synovitis secondary to a urinary tract infection and gastroenteritis. 47 patients (51.6%) did not have any of the predictors, and 6 patients (6.6%) had three or more positive predictors.

Conclusion: Although clinical predictors are helpful in distinguishing septic arthritis from transient synovitis, there were false negative and false positive findings in the study. The predictors cannot be considered alone, and ultimately clinical judgement must be exercised to ensure that cases of septic arthritis are not missed.

A careful study of children with transient synovitis of the hip has failed to establish any connection with infection by staphylococci or streptococci, with allergy, with viral infection and with trauma.

1. Transient synovitis is an acute, and at times exudative, condition of the synovial membrane.

2. There is no particular association with injury or with upper respiratory infection.

3. The course is short and benign with complete resolution. The occasional hip with chronic or recurrent symptoms can be distinguished from Legg-Perthes' disease by the shorter history, normal radiographs and the complete resolution.

4. There is no evidence that transient synovitis leads to avascular changes in the femoral head.