Ultrasound Case #6 – The Pad
A 65 year old female presents after a fall. She says that she fell onto her right hand. She notes that her elbow is very painful and hard to move. She denies injury to her head, LOC, nausea or vomiting.
You place a linear probe on the posterior aspect of her right elbow with the indicator pointed superiorly. You obtain the following images.
What do you see in these images and what type of injury are you suspecting?
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Clips 1 and 2 show a clear view of the posterior humerus (bright white line) coming down and meeting the olecranon. You can see the triceps muscle and tendon overlying these bones. Just above the distal humerus you note a triangular shaped collection of fluid elevating the surrounding structures. This is a small hematoma and in this location it leads to a posterior fat pad on X-ray. Therefore, in an adult, you would suspect a radial head or neck injury. Below is a labeled reference image.
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The US imaging here shows an effusion displacing the fat pad and tenting the triceps tendon. While no fracture can be identified, a posterior fat pad is 75-85% specific for an elbow fracture1. A radial head or neck fracture is by far the most commonly associated pathology when present (86%), with injuries otherwise occurring to the olecranon and lateral epicondyle2. Contralateral imaging can help clarify the presence of pathology should the presentation warrant.
POCUS works relatively well for quickly identifying elbow injuries. One study found that US correctly diagnosed all epicondyle injuries in a series of youth baseball players confirmed with radiographic imaging3. Compared to CT imaging, POCUS was 95% sensitive and 85% specific for elbow injuries4. To conduct the scan, use a linear probe and place it longitudinally along the distal posterior humerus. Rotate into short access and scan along the humerus, looking for suspicious effusions. Do the same along ulna and radius looking for any effusions of cortical disruptions. The image we have here is the longitudinal view of the olecranon.
While radiographs will likely remain the primary assessment of elbow injuries, there are still multiple applications for bedside ultrasound5. As an adjunct to indeterminate radiographs, especially in pediatric populations, POCUS will help to reduce the number of CT scans for these patients. You may also consider the modality when there is a low index of suspicion for injury. In more resource limited setting, POCUS can help to hasten the workup and treatment of these patients.
1. O’Dwyer, H. et al. The fat pad sign following elbow trauma in adults: Its usefulness and reliability in suspecting occult fracture. J. Comput. Assist. Tomogr. 28, 562–565 (2004).
2. POCUS for Elbow Injuries | POCUS_Toronto. Available at: http://www.pocustoronto.com/wordpress/?p=489. (Accessed: 18th January 2021)
3. Harada, M. et al. Using Sonography for the Early Detection of Elbow Injuries Among Young Baseball Players. Am. J. Roentgenol. 187, 1436–1441 (2006).
4. Avcı, M. et al. The comparison of bedside point-of-care ultrasound and computed tomography in elbow injuries. Am. J. Emerg. Med. 34, 2186–2190 (2016).
5. ACEP // Tips & Tricks: Supracondylar Fractures and POCUS. Available at: https://www.acep.org/how-we-serve/sections/emergency-ultrasound/news/march-2020/tips–tricks-supracondylar-fractures-and-pocus/. (Accessed: 18th January 2021)