Dynamic Ulnar Nerve Dislocation

Dynamic Ulnar Nerve Dislocation

Authors, Editors, Case Information Author: Steven Greenberg, MD, MS Affiliation: CMC Sports Medicine Co Author(s): David Price, MD Senior Editor: Wesley Troyer, DO Editor: Laura Mattson, DO Clinical Vignette: 40 yo Male describing shock-like sensation, numbness, pain and weakness in the left forearm with preacher curls. Numbness extends into the medial hand. Further evaluation found symptoms recurred with hyperflexion or hyperextension. Type of Probe Used: LA3-16AI Hockey-Stick transducer Positioned transverse and posterior on the right proximal upper extremity superior to the medial epicondyle. #1 - Image Short axis view of the ulnar nerve at the level of the medial epicondyle, with elbow positioned in approximately 70-90 degrees of flexion. This image demonstrates the ulnar nerve (yellow), medial epicondyle (blue) and medial head of the triceps (red) in its usual configuration, with the nerve within the ulnar groove. In this region, there was focal enlargement of the ulnar nerve, with maximal cross sectional area of 15mm2 (normal <10mm2). #2 - Image Short axis view of the ulnar nerve at the level of the medial epicondyle, with the elbow positioned in maximal flexion. Here the ulnar nerve is seen outside of the ulnar groove (dislocated), anterior to the medial epicondyle. #3 - Video View Video During dynamic ultrasound evaluation, the patient's elbow was flexed and the ulnar nerve was seen to dynamically dislocate out of the ulnar groove. With elbow extension, the nerve was seen to spontaneously reduce. During this assessment, the patient's typical symptoms were reproduced. In the attached video, we begin with the patient in a position of maximal elbow flexion, with the nerve already dislocated anterior to the medial epicondyle. With elbow extension, the nerve is then seen to relocate posterior to the medial epicondyle in its normal, anatomic position. Interpretation Image Interpretation: Focal enlargement and dynamic dislocation of the left ulnar nerve at the level of the medial epicondyle, consistent with ulnar nerve instability/mononeuropathy at the elbow. Teaching Pearl: Cubital tunnel syndrome is a peripheral neuropathy caused by chronic compression or repetitive trauma of the ulnar nerve at the elbow between the medial epicondyle of the humerus and the olecranon process of the ulna. Nerve irritation can be caused by anatomic damage from fracture of the medial epicondyle, osteophytes, infection, soft tissue mass or synovitis at the elbow joint. The nerve may also be damaged due to compression from tight or thickened surrounding tissues. Symptoms often occur with prolonged periods of elbow flexion like sleep, exercise, driving, typing or talking on a phone. Congenital laxity of the cubital tunnel retinaculum can result in hypermobility of the ulnar nerve, which can lead to repetitive subluxation when then elbow is flexed. In this case, the ulnar nerve is recurrently dislocated and relocated with flexion and extension (respectively) of the elbow, resulting in a tractional and frictional neuritis. Consider ulnar nerve instability when patients present with recurrent numbness/tingling and pain with flexion of the arm, especially with curling movements.
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