|In the ED, a burning hip is never sexy. Fact.|
And so it remains a hot topic because we would like to avoid having to perform hip arthrocentesis (the diagnostic gold standard) in every child with a clinical suspicion for SA.
Fortunately there may indeed be a way to forego unnecessary invasiveness with the use of adjunctive bedside ultrasound of the hip--a rather rapid and simple test to perform!
|Probe angle aligns with natural femoral head angulation|
- Use high-frequency linear probe, MSK exam setting, patient supine.
- Scan both hips for comparison, starting with unaffected side
- Normally synovial space is < 5 mm wide (greater is considered effusion)
- Normally < 2 mm difference in synovial spaces (left vs right). Any greater is + effusion
|Note the large synovial space on L hip|
|9.2 mm joint effusion (> 5 mm is positive)|
In 2006 Zamzam retrospectively studied 154 children (mean age 4.3) with painful hip suspicious of TA vs SA (clinical grounds and lab work) (3)
- Children sent off for diagnostic u/s
- Primary outcome: diagnosis of SA and to differentiate from TS
- Physical exam, history, and labs with XR: sensitivity 74% specificity 74% and 76% PPV
- ultrasound findings alone: sens 86.4% spec 89.7% PPV 87.9%
- Ultrasound alone preforms better than exam findings combined labs/XR
- Neither is sensitive/specific enough to use in isolation
- Perhaps combining ultrasound with a good exam and some labs could be enough to forego joint aspiration? ...
- Categorized into three tertiles based on physical exam findings (mild, moderate, severe irritable hip)
- All had ultrasound of hips done after physical exam
- no effusion on u/s with mild-mod exam -- idiopathic pain, w/u stopped there.
- effusion (clear) with mild/mod exam -- TS presumed, w/u stopped. (A few got XR for family reassurance). No labs, no aspirate.
- effusion (turbid) with moderate/severe exam -- SA presumed, w/u with labs and aspiration of hip
- 2 positive aspirate result (SA), 10 with negative aspirates (TS)
- No child had diagnosis changed from initial at the 3 year follow up
While the latter study remains a bit cavalier to most US-based emergency physicians it offers hope and promise that ultrasound, when combined with a good history and physical exam and, when warranted, lab data can prevent unnecessary use of radiation, admissions, antibiotics (empiric), and painful procedures.
A good approach may be:
- History and physical exam followed by bedside ultrasound
- No effusion and reassuring (minimal Kocher present) clinically?
- close follow-up with NSAIDs
- Concerning clinically (> 2-3 Kocher or strong suspicion based on H+P) with effusion
- labs + CRP* (5), XR, and ortho consult vs. ultrasound-guided aspiration
What's your take?
- M.S. Kocher, D. Zurakowski, and J.R. Kasser, "Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm.", The Journal of bone and joint surgery. American volume, 1999.
- S.J. Luhmann, A. Jones, M. Schootman, J.E. Gordon, P.L. Schoenecker, and J.D. Luhmann, "Differentiation between septic arthritis and transient synovitis of the hip in children with clinical prediction algorithms.", The Journal of bone and joint surgery. American volume, 2004
- M.M. Zamzam, "The role of ultrasound in differentiating septic arthritis from transient synovitis of the hip in children.", Journal of pediatric orthopedics. Part B, 2006.
- C Konstantoulakis, "Initial diagnostic approach of the irritable hip in childhood: is ultrasound really useful?"Acta. Orthop. Belg. 2011, 77.
- *M.S. Caird, J.M. Flynn, Y.L. Leung, J.E. Millman, J.G. D'Italia, and J.P. Dormans, "Factors distinguishing septic arthritis from transient synovitis of the hip in children. A prospective study.", The Journal of bone and joint surgery. American volume, 2006.