PEM POCUS Series: Hip Effusion
Read this tutorial on the use of point of care ultrasonography (POCUS) for pediatric hip effusion. Then test your skills on the ALiEMU course page to receive your PEM POCUS badge worth 2 hours of ALiEMU course credit.
PATIENT CASE: Child with a Limp
Sarah is a 4-year-old girl who comes into the emergency department complaining of a limp for the last day. She had an upper respiratory infection which started a week ago for which she had been taking acetaminophen and ibuprofen with her last dose of either being 2 days ago. Those symptoms have improved. Yesterday, she started complaining of diffuse right leg pain primarily at her hip, thigh, and knee. Today, her parents noted she was walking with a limp.
On arrival, her vital signs are:
| Vital Sign | Finding |
|---|---|
| Temperature | 100.1F |
| Heart rate | 100 bpm |
| Blood pressure | 97/50 |
| Respiratory rate | 19 |
| Oxygen saturation (room air) | 100% |
She is well appearing and walks with an antalgic gait favoring the left leg. She has a normal HEENT, neck, cardiac, respiratory, abdominal, and back examination. She points to her right anterior thigh when you ask her where her pain is. She has limited range of motion with internal and external rotation of her right hip and complains of pain. She cries when you palpate any part of her leg, but is able to range her knee, ankle, and foot fully. She has 2+ dorsalis pedis and posterior tibialis pulses and intact sensation to light touch throughout.
Given her pain with range of motion at her hip, you order a hip radiograph, but while waiting for it, decide to perform a hip point of care ultrasound (POCUS) examination.
PEDIATRIC HIP EFFUSION: Ultrasound Technique
It can be difficult for children to locate the exact area of pain and often hip pain can present with referred knee and thigh pain. A thorough physical examination along with hip POCUS can help localize the area of discomfort. When we use POCUS to evaluate the hip, we are primarily looking for a joint effusion in the synovial space. This is best visualized anterior to the femoral neck.
Technique
- The patient should be positioned supine.
- Depending on the age of the child, the child can be positioned supine in the guardian’s lap while undergoing the examination.
- Offering the child a toy, book, or phone/tablet for distraction during the examination can also help ease anxiety.
- Use a linear high frequency transducer with a wide footprint.
- Place the transducer along the anterior hip.
- Use the greater trochanter as a lateral landmark and place the probe on top of the femoral head and neck (Figure 3)
- Aim the probe marker towards the patient’s umbilicus.
- Identify the anatomical landmarks on ultrasound (figure 4)
- Hip muscles: Sartorius, quadriceps, and iliopsoas
- Bones: Femoral head, femoral neck
- The area of interest in looking for a hip effusion is the synovial space anterior to the femoral neck and NOT anterior to the femoral head. This area is also referred to as the anterior synovial recess.
- Tips:
- It is often helpful to ultrasound the unaffected side as a comparison.
- Be aware of the patient’s comfort throughout the examination.
ABNORMAL ULTRASOUND FINDINGS
A hip effusion will appear anechoic (black) in the synovial space anterior to the femoral neck (anterior synovial recess). Measure the distance between the anterior surface of the femoral neck and the posterior surface of the iliopsoas muscle. Examples are illustrated in figures 5 and 6.
There have been different methods used to assess if an effusion is present including:1,2
- Measured effusion is >0.5 cm
- Measured effusion with >0.2 cm difference compared to the contralateral hip
- Gestalt view with the anterior synovial recess areas appearing asymmetric compared to the other hip
Limitations of the Hip POCUS
Note that hip POCUS does not tell you the cause of an effusion but rather only whether an effusion is present or not. Effusions can result from infectious, inflammatory, and traumatic etiologies, and thus it is important to take into account the context of the patient’s presentation.
References
- Vieira R, Levy J. Bedside ultrasonography to identify hip effusions in pediatric patients. Ann Emerg Med. 2010;55(3):284-289. PMID 19695738
- Cruz C, Vieira R, Mannix R, Monuteaux M, Levy J. Point-of-care hip ultrasound in a pediatric emergency department. Am J Emerg Med. 2018;36(7):1174-7. PMID 29223689
FACTS and LITERATURE REVIEW
There have been multiple case reports of hip POCUS identifying hip effusions in children with fractures, septic joints, and in the work-up of children with limps [1–4]. There are limited studies examining the accuracy of hip POCUS compared to radiology-performed ultrasounds in children. The studies that exist show high sensitivity and specificity when hip POCUS is performed by pediatric emergency medicine (PEM) physicians (Table 1).
Additional studies have explored the development of hip effusion clinical decision-making tools to support POCUS in the diagnosis of transient synovitis and differentiate it from other causes of non-traumatic arthritis in patients with a hip effusion, including septic arthritis, Lyme arthritis, and osteomyelitis [5]. For example, one retrospective pilot study found that the combination of POCUS performed by PEM physicians and a clinical decision rule could correctly rule in transient synovitis in 63 of 67 patients with a hip effusion [6].
The use of POCUS in the ED has also been associated with cost savings and greater clinical efficiency. In pediatric patients, hip POCUS has demonstrated potential cost-saving benefits compared with radiology-performed ultrasound. One Australian economic evaluation estimated annual savings of approximately AU$35,800 (about US$25,000), mainly by shortening the time children spent in an ED bed waiting for an ultrasound [7]. Additionally, in a case series of 10 children with septic arthritis of the hip, POCUS-guided hip aspiration by a PEM-trained physician was associated with a shorter time to antibiotic administration [1].
Although standardized training requirements for hip effusion POCUS in pediatric patients have not been established, scanning accuracy appears to be influenced by operator experience and confidence. As illustrated in Table 1, sensitivity and specificity were higher among physicians who had performed more hip POCUS scans and among those with greater confidence in their ultrasound skills [8,9,11]. These findings highlight the importance of continued practice and experience in developing proficiency in hip POCUS, ultimately improving diagnostic accuracy and supporting timely clinical decision-making. So, make sure to keep scanning!
| Study | N | Sensitivity | Specificity | Comments |
|---|---|---|---|---|
| Vieira et al., Ann Emerg Med, 2010 [8] | 28 | 85% | 93% | If the pediatric emergency physician had a high confidence in ultrasound accuracy, the sensitivity increased to 90% and specificity to 100%. |
| Cruz et al., Am J Emerg Med, 2018 [9] | 516 | 85% | 98% | For each additional hip POCUS performed, the odds of an accurate scan increased by 2.4%. |
| Katz-Dana et al., CJEM, 2024 [10] | 95 | 89.8% | 91.3% | Strong positive LR of 10.33 and negative LR of 0.11 for PEM physician-performed POCUS. |
| Jones et al., Ann Emerg Med, 2025 [11] | 161 (322 hips) | 89.3% | 99.2% | For the 3 high-volume pediatric emergency physicians, sensitivity and specificity increased to 98.1% and 97.8%, respectively. Sensitivity and specificity are per hip. |
References [click to expand] +
- Berant R, Bder M, Kaufman-Shriqui V, Shahar-Nissan K. Point-of-Care Ultrasound-Guided Aspiration of the Hip Joint by an Emergency Medicine Physician: A Pediatric Retrospective Case Series. Pediatr Emerg Care. 2022;38(3):139-142. doi:10.1097/PEC.0000000000002650. PMID: 35226624.
- Deanehan J, Gallagher R, Vieira R, Levy J. Bedside hip ultrasonography in the pediatric emergency department: a tool to guide management in patients presenting with limp. Pediatr Emerg Care. 2014;30(4):285-287. doi:10.1097/PEC.0000000000000113. PMID: 24694889.
- Garrison J, Nguyen M, Marin J. Emergency Department Point-of-Care Hip Ultrasound and Its Role in the Diagnosis of Septic Hip Arthritis: A Case Report. Pediatr Emerg Care. 2016;32(8):555-557. doi:10.1097/PEC.0000000000000874. PMID: 27490732.
- Tsung J, Blaivas M. Emergency department diagnosis of pediatric hip effusion and guided arthrocentesis using point-of-care ultrasound. J Emerg Med. 2008;35(4):393-399. doi:10.1016/j.jemermed.2007.10.054. PMID: 18403170.
- Chan N, McCreary DJ, Nedyalkova A, Snelling PJ. Point-of-care ultrasound for the diagnosis of hip effusion in children presenting to the emergency department with atraumatic limp or hip pain: a scoping review. J Ultrasound Med. 2026;45(10):2109-2118. doi:10.1002/jum.70286. PMID: 42104527.
- McCreary DJ, Chowdhury R, Hamilton C. Can a POCUS Clinical Decision Rule Improve Reliability in the Diagnosis of Paediatric Transient Synovitis of the Hip? A Single Centre Pilot Study. POCUS J. 2025;10(2):103-108. doi:10.24908/pocusj.v10i02.18290. PMID: 41322175.
- Bailey C, Deane H, O’Brien A, Dalziel K. An economic evaluation of point-of-care ultrasound for children presenting to the emergency department with suspected septic arthritis of the hip. Aust Health Rev. 2024;48(1):37-44. doi:10.1071/AH23214. PMID: 38266497.
- Vieira R, Levy J. Bedside ultrasonography to identify hip effusions in pediatric patients. Ann Emerg Med. 2010;55(3):284-289. doi:10.1016/j.annemergmed.2009.06.527. PMID: 19695738.
- Cruz C, Vieira R, Mannix R, Monuteaux M, Levy J. Point-of-care hip ultrasound in a pediatric emergency department. Am J Emerg Med. 2018;36(7):1174-1177. doi:10.1016/j.ajem.2017.11.059. PMID: 29223689.
- Katz-Dana H, Stackievicz R, Dana E, et al. Diagnostic accuracy of point-of-care ultrasound (PoCUS) for the diagnosis of hip effusion in the pediatric emergency department. CJEM. 2024;26(12):875-882. doi:10.1007/s43678-024-00788-z. PMID: 39352610.
- Jones RM, Malia L, Snelling PJ, et al. Diagnostic Accuracy of Point-of-Care Ultrasound for Hip Effusion: A Multicenter Diagnostic Study. Ann Emerg Med. 2025;86(6):566-575. doi:10.1016/j.annemergmed.2025.04.033. PMID: 40481828.
CASE RESOLUTION
The patient’s hip plain film radiographs are unremarkable. You decide to incorporate hip POCUS to your evaluation. You place a linear, high-frequency transducer and visualize the patient’s bilateral hips. You observe the following:
Right Hip (Affected Side) POCUS Video and Key View
Though the child complained of hip, knee, and thigh pain, your POCUS evaluation identifies a right hip effusion which helps you narrow the location of her pain.
Left Hip (Normal Side) POCUS Video and Key View
ED Course
The patient’s labs result, and she has reassuring labs, which include a serum WBC 8.3 x109/L and ESR 34 mm/hr. The patient receives ibuprofen during her visit and within 1 hour is able to walk without a significant limp and states she feels better. The patient’s family notes they have spent the last few weeks of summer in a Lyme-endemic region, and so you send off Lyme titers.
Given the resolution of limp, lack of fever, and reassuring lab values, you do not believe the patient has a septic joint. Her effusion is more likely the result of a transient synovitis. You recommend close pediatrician follow-up.
Pediatrician Clinic Follow-Up
At her pediatrician clinic visit 1 week later, her Lyme titers return negative, and the patient continues to be limp-free.
The PEM POCUS series was created by the UCSF Division of Pediatric Emergency Medicine to help advance pediatric care by the thoughtful use of bedside ultrasonography.
Read other PEM POCUS tutorials. Learn more about bedside ultrasonography on the ALiEM Ultrasound for the Win series.
