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Septic arthritis in children
BMJ 2010; 341 doi: 10.1136/bmj.c4407 (Published 7 October 2010)
Septic arthritis accounts for a small minority of the myriad musculoskeletal problems in childhood which primary care doctors will evaluate. Joint infections are best treated early to avoid potentially disabling complications. The earlier the presentation, the more difficult it is to distinguish an infection from benign, self limited conditions such as transient synovitis of the hip.
Case scenario
A 5 year old boy is brought to the accident and emergency department with pain in his left leg. The previous day he limped markedly and now he refuses to walk. History is negative for injury and positive for fever in a previously well, immunised child who is developmentally normal. Concerned about septic arthritis, the junior doctor requests a blood count, erythrocyte sedimentation rate, and C reactive protein concentration, and requests review by the paediatric team.
How common is it?
Transient synovitis is a common idiopathic inflammatory condition of the child’s hip which presents in a similar manner to the “do not miss” diagnosis of septic arthritis
Transient synovitis was diagnosed in 43 Norwegian children per 100 000 annually, compared with only five cases of septic arthritis per 100 0001
Septic arthritis in children affects the hip in a third of cases, the knee in a third, and other joints in the remaining third2
Septic arthritis can occur at any age in childhood but is most common among infants, toddlers, and children of preschool age2
Why is it missed?
Joint infections overlap in presentation with transient synovitis, unexplained symptoms, and minor trauma, all of which are common. Musculoskeletal infections in very young children and in very ill children can be missed because the symptoms and signs that localise the problem are absent. Untreated pyogenic infection eventually “declares itself,” but this may be too late for optimal treatment. Antibiotic treatment before diagnosis (prescribed for other conditions or empirically) may mask clinical findings without curing the disease.
Why does this matter?
Missed septic arthritis results in severe destruction of the child’s hip, which is difficult to treat.3 4 A prospective cohort study of all children presenting with septic arthritis of the hip in South Africa found no sequelae among children diagnosed and treated within five days of onset of symptoms, but a very high incidence of permanent problems among those treated at five days or later.5 Late treatment cannot reverse the damage, caused by pus under pressure and compromised blood flow, to the joint cartilage, the epiphyseal bone, or the growth plate. Unfortunately, more than two thirds of the children in the South African series were treated late, with delay in diagnosis (rather than delay in presentation) the most common reason for delay in treatment. Diagnostic delay may be less common in high income countries, but our paediatric orthopaedic unit treats many patients with ongoing sequelae of septic arthritis and sees 5-10 new late cases every year.
How is it diagnosed?
The presentation of septic arthritis is fever with limb pain, limp, or refusal to bear weight. The affected joint is held in the position of comfort, which maximises intracapsular volume. At the hip, flexion, abduction, and external rotation are typical. Muscle spasm or pain with attempts to internally rotate or “log roll” the affected hip indicates effusion, but does not distinguish septic arthritis from transient synovitis.
The younger the child, the more difficult the clinical examination. Neonates may have few localised signs and a blunted systemic response, presenting instead with “pseudoparalysis” of the affected limb.
No single test can reliably distinguish infection from inflammation, and this has led to diagnostic algorithms combining criteria. Kocher proposed the first such algorithm, identifying refusal to bear weight, fever >38.5ºC, erythrocyte sedimentation rate >40 mm/h, and white blood cell count >12.0×109/l as four criteria distinguishing septic arthritis from transient synovitis.6 If none of these criteria was positive, the probability of septic arthritis was less than 0.2%; probability rose to 3% if one criterion was positive, 40% if two were, 96% if three were, and 99% if four were. Subsequent prospective studies showed reduced but still acceptable diagnostic performance (area under receiver operating curve 0.86)7; other researchers have added C reactive protein >200 mg/l or a history of a previous healthcare visit to improve diagnostic accuracy.8 9
Plain radiography shows nothing for the vast majority of children presenting with transient synovitis or septic arthritis. In general practice, plain radiographs are not a first line test, except in children 9 years and over to look for slipped upper femoral epiphysis.10
Ultrasound scans are sensitive to hip joint effusion but cannot distinguish septic arthritis from transient synovitis. They give many false negative results in early presentations or in bilateral disease.11
Blood cultures can be obtained but are positive only about 30% of the time.2 Usually the child is being treated before any culture results come back.
A practical approach in primary care is to consider a complete blood count, erythrocyte sedimentation rate, and C reactive protein in any child who refuses to walk or who has a high fever with bone or joint pain or tenderness. The indications for drawing blood have not been studied, but the paper by Kocher (based on data from tertiary care) showed that of 82 children with septic arthritis, 78 refused to walk and four could walk with a limp, whereas of 86 with transient synovitis only 30 refused to walk.6 In Kocher’s series the mean recorded temperature for patients with septic arthritis was 38.7º C, compared with 37.4º C among patients with transient synovitis.
When blood is drawn, white cell count, erythrocyte sedimentation rate, C reactive protein, non-weightbearing, and fever constitute separate diagnostic criteria. If none or one diagnostic criterion (red flags) is positive, the child can be safely sent home and reviewed in 24 to 48 hours provided that parents can bring the child for re-evaluation if the condition worsens. We typically advise parents to give ibuprofen and restrict activity for such children. If two or more diagnostic criteria are present, or if the child’s condition worsens, a specialist should be consulted. The diagnosis is confirmed by finding pus on aspiration of the joint.
How is it managed?
Septic arthritis is managed in consultation with an orthopaedic surgeon. Management includes arthrotomy to decompress the joint, remove infected material, and reduce the chances of sequelae from avascular necrosis or damage to the growth plate. Ideally arthrotomy is performed promptly and antibiotics are begun only after intraoperative cultures are taken (or before this on the advice of the surgeon). Although recent case series have shown acceptable results with repeated joint aspiration alone,12 13 there is insufficient evidence to recommend this as routine practice. The current practice of the orthopaedic author (AH) includes arthrotomy in all cases of hip joint sepsis, and in most cases of sepsis of the knee or shoulder.
Key points
Septic arthritis in children can be difficult to diagnose, and to distinguish from more common conditions such as minor trauma or transient synovitis of the hip
Early diagnosis and treatment of septic arthritis is important to avoid joint destruction and disability
Fever, weightbearing status, white cell count, erythrocyte sedimentation rate, and C reactive protein are considered together for diagnosis
Children with two or more “positive” diagnostic criteria should be referred for prompt evaluation by a specialist, whereas children with no or one positive criterion can safely be watched
Notes
Cite this as: BMJ 2010;341:c4407
Footnotes
This is one of a series of occasional articles highlighting conditions that may be more common than many doctors realise or may be missed at first presentation. The series advisers are Anthony Harnden, university lecturer in general practice, Department of Primary Health Care, University of Oxford, and Richard Lehman, general practitioner, Banbury. If you would like to suggest a topic for this series please email us ([Ссылки доступны только зарегистрированным пользователям ]).
Contributors: AH and MW collaborated on the research, deriving clinical recommendations, and writing. AH is guarantor.
Competing interests: All authors have completed the unified competing interest form at [Ссылки доступны только зарегистрированным пользователям ] (available on request from the corresponding author) and declare no support from any organisation for the submitted work; no financial relationships with any organisation that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Not commissioned; externally peer reviewed.