Ran Goldman, MD (biography and disclosures)
What frequently asked question I’ve noticed
Acute limping is a very common chief complaint among children visiting a clinic or an emergency department . The main differential diagnosis includes arthritis (viral or bacterial), osteomyelitis, Legg-Calve-Perthes disease (idiopathic avascular necrosis) and slipped capital femoral epiphysis.
One of the most common reasons for acute limping is Transient Synovitis, also named ‘A-septic Arthritis’ . This condition, representing a viral infection in a large joint, is most common between 3 and 10 years of age, with a mean age of 6 years. It occurs more frequently in boys and in vast majority of cases is unilateral (>90%).
Children are usually symptomatic for 24-48 hours before their parents seek advice from a health care provider. They may limp or not bear weight on the affected leg. They may have a low grade fever, albeit most patients are a-febrile. The hip is the most common joint involved in the process.
One of the key elements in illness history, that help with the diagnosis of transient synovitis, is the description of a preceding viral illness, usually 2 to 3 weeks prior to their presentation .
While transient synovitis is a very benign condition that will resolve spontaneously in a few days, and is treated with analgesia, it may be confused with a much more severe condition – Septic Arthritis – a bacterial infection. The importance in differentiating between the two conditions is the fact that septic arthritis will necessitate an immediate action for diagnosis (tapping the joint) and treatment (IV antibiotics and admission).
Data that answers this question
So how can one differentiate between transient synovitis and septic arthritis?
Clinical exam – this is the most important differentiator. Children with septic arthritis look sick. They are unwell, tired, possibly lethargic and will do very little activity. With transient synovitis, parents may report limping as the only ‘new’ finding, as the child will likely be active, alert, feed and in general – will look well.
Physical examination – Examination in young, non-cooperative children, is always challenging. When the child is cooperative, he or she may have limited range of motion (mostly internal rotation of the hip), and with septic arthritis children will usually be guarding their joint and avoid movement as much as they can.
Plain x-ray of the hip – similar to clinical and physical exam, a plain x-ray may not be as beneficial in distinguishing between the two diagnoses, as evidence of some effusion and widening of the joint space may be evident in both conditions.
Blood tests – In transient synovitis the white blood cells count, differential count, sedimentation rate (ESR) and other inflammatory markers (CRP) are usually within normal limits, while in septic arthritis they are usually elevated. This differentiation however may not be evident in the first few days of illness, and normal counts should not be used as a measure to rule-out septic arthritis. Procalcitonin  has not been shown to be of benefit in differentiating the conditions.
Prediction rule  – In an effort to provide a combined diagnostic test for septic arthritis (of the hip), four independent predictors (history of fever, no weight-bearing on exam, ESR of 40 mm/hr, and a serum white blood cell count of >12,000 cells/mm(3)) were identified and validated as a reliable measure.
Practice tip in managing this problem
When children with a limp present to you, always consider the possibility of septic arthritis. The key element in deciding on tapping the joint, referring to an emergency department or an orthopedic surgeon or ordering an ultrasound is the clinical presentation of the child. When in doubt or if there is no good follow-up available – draw blood work, and order a plain x-ray of the joint. Give ibuprofen to relieve the pain and reassess the child after 20-30 minutes as limping and pain from transient synovitis should improve. When the child looks unwell – an urgent tapping of the joint and systemic antibiotic therapy is needed.
References / Additional reading (Note: Article requests might require a login ID with CPSBC or UBC)
- Krul M, van der Wouden JC, Schellevis FG, van Suijlekom-Smit LW, Koes BW. Acute non-traumatic hip pathology in children: incidence and presentation in family practice. Fam Pract. 2010;27(2):166-170 (View article)
- Fischer SU, Beattie TF. The limping child: epidemiology, assessment and outcome. J Bone Joint Surg Br. 1999;81(6):1029-1034 (View article)
- Kastrissianakis K, Beattie TF. Transient synovitis of the hip: more evidence for a viral aetiology. Eur J Emerg Med. 2010;17(5):270-273 (View article with CPSBC or UBC)
- Butbul-Aviel Y, Koren A, Halevy R, Sakran W. Procalcitonin as a diagnostic aid in osteomyelitis and septic arthritis. Pediatr Emerg Care. 2005;21(12):828-832 (View article with CPSBC or UBC)
- 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;86-A(8):1629-1635 (View article with CPSBC or UBC)