Written by Chris Thom
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In this multicenter prospective trial, emergency physicians had high accuracy in detection of hip joint effusions on point-of-care ultrasound. Watch the YouTube video to see these techniques in action!
The hip joint is a friendly place for ultrasound imaging
This was a 5-center prospective study of Emergency Department (ED) pediatric patients receiving radiology-performed hip ultrasound (RPUS) as part of their clinical evaluation. The most common indications were limp, refusal to bear weight, and joint pain. ED physicians, blinded to the RPUS, performed a point-of-care ultrasound (POCUS) of the hip, which was then compared to RPUS as the reference standard. 161 participants with 322 hip examinations were included.
There were 18 ED physicians enrolling patients, with 3 accounting for 61.5% of the cases. The sensitivity of the three high volume physicians was 98.1% (95%CI 88.8-99.9) and specificity was 97.8% (95%CI 86.8-99.9). The remainder of the ED physicians had a sensitivity of 83.3% (95%CI 61.8-94.5) and specificity of 97.4% (95%CI 84.6-99.9)
How does this change my practice?
ED physician-performed hip ultrasound can be a powerful tool in expediting diagnostic workups and guiding ED physician-performed hip arthrocentesis. You certainly don’t have to limit yourself to the Kocher criteria or the modified Kocher criteria when you can very easily image the hip as part of initial evaluation and have the answer of “effusion” or “no effusion” from the outset. That diagnostic information can appropriately influence differential diagnoses and determine which patients might benefit from an attempted arthrocentesis. It is an easy exam to master, but like many things with POCUS, a bit of dedicated training is indispensable to achieve test characteristics as demonstrated in this study. Indeed, the three “super user” ED physicians had appreciably higher diagnostic accuracy than the other individuals.
POCUS pro-tips and clips:
The area to focus on with the hip effusion evaluation is the femoral neck. The joint effusion will accumulate anterior to the femoral neck and not directly in the space between the acetabulum and the femur. You’ll want to align your ultrasound probe with the long axis of the femoral neck and then look for anechoic fluid between the femoral neck and the iliopsoas muscle. Occasionally, the muscle can appear hypoechoic itself, which can lead to false positives. Including the other hip can help mitigate this, as can slow fanning of the probe left and right through the area in question. The measurements are very helpful to have in mind (5 mm in size or > 2 mm in asymmetry), but occasionally early or small effusions might not quite meet these thresholds. I find symmetry evaluation with the contralateral hip very helpful in these cases. See this YouTube video for more details on this article and to see real-time video of these techniques in action!
Source
Diagnostic Accuracy of Point-of-Care Ultrasound for Hip Effusion: A Multicenter Diagnostic Study. Ann Emerg Med. 2025 Jun 7:S0196-0644(25)00279-3. doi: 10.1016/j.annemergmed.2025.04.033. Epub ahead of print. PMID: 40481828
