Image Interpretation: Dynamic ultrasound demonstrates anterior dislocation of the ulnar nerve with elbow flexion, followed by subluxation of the medial head of the triceps muscle over the medial epicondyle. With elbow extension, the medial triceps and subsequently the ulnar nerve snap posteriorly back into the retrocondylar groove. The ulnar nerve is normal in caliber and echotexture. No anconeus epitrochlearis muscle is identified.

Teaching Pearl: Snapping triceps syndrome is a relatively uncommon cause of medial elbow pain, caused by dynamic displacement of the medial triceps over the medial epicondyle during elbow flexion, often with ulnar nerve instability or dislocation. Patients may report palpable or audible snapping, and ulnar neuropathy symptoms may be present but are not required. Dynamic ultrasound is the best way to demonstrate the sequence of motion: ulnar nerve subluxation or dislocation, followed by medial triceps translation and reduction with elbow extension. This distinction matters because treatment directed only at the ulnar nerve may fail if snapping triceps is not also recognized and addressed. References: 1. Xia WZ, Abukar A, Moosavi H, Nandi N, Rashid A. Snapping triceps syndrome: a review of the literature and proposed operative treatment algorithm. JSES Rev Rep Tech. 2026;6(1):100580. doi:10.1016/j.xrrt.2025.08.017 2. Jacobson JA, Jebson PJ, Jeffers AW, Fessell DP, Hayes CW. Ulnar nerve dislocation and snapping triceps syndrome: diagnosis with dynamic sonography: report of three cases. Radiology. 2001;220(3):601-605. doi:10.1148/radiol.2202001723 3. Ooi MWX, Tham JL, Al-Ani Z. Role of dynamic ultrasound in assessment of the snapping elbow and distal biceps tendon injury. Ultrasound. 2022;30(4):315-321. doi:10.1177/1742271X211057204 Disclaimer: No financial disclosures. The views expressed herein are those of the authors and do not reflect the official policy of the Department of the Army, Department of the Air Force, Defense Health Agency, Uniformed Services University, Department of War, or the U.S. Government.