1051 - Dynamic Ultrasound in Diagnosing Ulnar Nerve Compression: A Case Report of an Anconeus Epitrochlearis Accessory Muscle in a Baseball Player

Thursday, February 22, 2024

5:00 PM – 6:30 PM EDT

Co-Author(s)

MA

Marielle Araujo, MD

PM&R Resident
Northwell Health
West. Hempstead, New York, United States

Presenting Author(s)

EC

Elizabeth Cipparrone, DO

Resident
Northwell Health
Manhasset, New York, United States

Co-Author(s)

TL

Todd Lefkowitz, DO

PM&R Attending/ Associate Program Director
Northwell Health
Bay Shore, New York, United States

Case Diagnosis: Chronic elbow pain in a baseball player found to have dynamic ulnar nerve compression from an anomalous accessory muscle.

Case Description: A 20-year-old male collegiate baseball player with a history of medial epicondylar apophysitis (ie, Little League Elbow) was referred to physiatry for chronic right elbow pain.  The patient endorsed medial-sided elbow pain for the past five years with associated paresthesias in the ulnar side of the forearm and hand, worsening over several months.  X-rays of the patient’s elbow were unremarkable. Electrodiagnostic evaluation revealed no evidence of an ulnar mononeuropathy across the elbow. Ultrasound of the medial elbow was significant for a small linear tear of the ulnar collateral ligament worse with valgus stress, as well as an anomalous anconeus epitrochlearis muscle.  Dynamic imaging of the patient’s elbow through flexion and extension range of motion showed crowding of the ulnar nerve by the anconeus epitrochlearis muscle against the medial epicondyle.  The cross-sectional area of the ulnar nerve at the level of the medial epicondyle and olecranon was 15mm², twice the normal.

Discussions: Dynamic ultrasound emerged as a pivotal tool in this case, offering real-time assessment of the UCL, ulnar nerve and muscular structures on the medial side of the elbow. This capability allowed for the identification of an anatomical variant, the anconeus epitrochlearis muscle, causing intermittent ulnar nerve compression. Conventional imaging modalities and EMG might have overlooked this dynamic compression, highlighting the advantage of dynamic ultrasound.

Conclusions: This case report emphasizes the significance of dynamic ultrasound in assessing structures vulnerable to episodic compression.  Anconeus epitrochlearis is prevalent in 4-34% of the population however, the incidence of causing ulnar neuropathy is unknown. As an evolving diagnostic tool, dynamic ultrasound holds promise in enhancing the accuracy of musculoskeletal diagnoses, especially in athletes with nuanced anatomical variations affecting performance and function.