A limping child is a common presentation to ED, and often a diagnostic dilemma.
What is Septic arthritis?
It is an infection in the joint capsule- approx 80% involve the lower limbs.
Occurs either via localised infection, or haematologenous spread.
Risk Factors: Un-vaccinated child, child <2, immunocompromised.
Red flags: Fever, unable to weight bare, decreased range of movement, pain swelling and redness of the joint.
What is Transient Synovitis?
This is inflammation of the joint capsule and synovial fluid, often occurring 1-2 weeks post viral infection.
Often very similar to septic arthritis, and present with fever, refusal to weight bare, decreased range of movement.
Sometimes improves with NSAIDS.
Transient synovitis is self limiting, however Septic arthritis if untreated can lead to osteomyelitis, joint destruction, growth arrest etc. Therefore missed diagnosis can be life changing.
How can I tell the difference?
Any child with a fever and a limp has septic arthritis until proven otherwise.
In 1999 Kocher published 4 criteria which retrospectively reviewed an irritable hip.
The 4 criteria included:
Non weight bearing
ESR= or > 40
WBC= or > 12,000
This gives a score of 0-4 and a percentage change of septic arthritis:
Importantly a child with a fever and a limp already has a 40% change of septic arthritis.
This study only evaluated in children with irritable hips, and therefore needs to be used with caution in other painful joints, but can still be useful.
How do I approach this child in ED?
NSAIDS, EMLA, Xray.
Good history and examination to rule out other causes such as non-accidental injury, trauma, toddlers fractures etc.
Bloods and cultures
In a well child delay antibiotics in order to gather an accurate diagnosis and synovial fluid culture
Keep the child NBM
Early discussions with Orthopaedics to facilitate further investigations.
Kocher MS1, Zurakowski D, Kasser JR. Differentialting between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999 Dec;81(12):1662-70