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Final Program


Final Congress Guide

Clinical Sciences/Health Conditions

300 Section - Safe Needle Trajectory for Flexor Carpi Ulnaris Electromyography: Ultrasonographic Evaluation of Optimal Insertion Angle and Effect of Elbow Position

Wednesday, May 20, 2026
6:00 PM - 7:30 PM PT

    Presenting Author/Autor expositor(s)

  • SP

    Sunjung Park, MD

    Resident Physician
    Korea University Guro Hospital
    Seoul, Seoul-t'ukpyolsi, Republic of Korea

    • Co-Author/Coautor(s)

  • KK

    Kyunghun Kang, MD

    Resident Physician
    Korea University Guro Hospital
    Guro-gu, Seoul-t'ukpyolsi, Republic of Korea

  • JY

    Joon Shik Yoon, M.D., Ph.D.

    Professor
    Korea University Guro Hospital
    Guro-gu, Seoul-t'ukpyolsi, Republic of Korea

  • GY

    GEUMJU YOON, BS

    Research Associate
    Korea University Guro Hospital
    Guro-gu, Seoul-t'ukpyolsi, Republic of Korea

  • EK

    EUNAE KOH, BS

    Research Associate
    Korea University Guro Hospital
    Guro-gu, Seoul-t'ukpyolsi, Republic of Korea

Objectives : Since needle electromyography is often performed without ultrasound guidance, defining precise anatomical relationships is essential to minimize nerve injury. This study quantified the relationship between flexor carpi ulnaris (FCU) and ulnar nerve, evaluated the effects of elbow flexion, and determined an optimal insertion angle as a safer alternative to perpendicular insertion.

Design: In eleven healthy volunteers, the probe was placed perpendicular to the ulna for short-axis views. At maximal FCU cross-sectional area (CSA), transverse distance from the ulna and skin depth were measured for the FCU center and the ulnar nerve in both elbow extension and 90° flexion. The safety zone was defined as a 5 mm transverse distance from the ulnar nerve. The optimal insertion site was determined by projecting a line from this safety limit through FCU center to skin, from which the insertion angle and needle length were calculated.

Results: Maximal CSA was observed at 30%–40% of forearm length. In extension, the FCU center was 14.5±3.1 mm anterior to the ulna at a depth of 8.2±1.3 mm, while nerve depth was 12.9±1.9 mm. Transverse distance between the FCU center and the ulnar nerve was 0.5±0.8 mm, whereas elbow flexion significantly increased this distance to 1.8±1.3 mm (p=0.001). Safety zone simulation identified optimal insertion site to be 22.5±2.6 mm anterior to the ulna, requiring 11.3±2.0 mm needle length and 43.7±7.8° anterior insertion angle.

Conclusion:

For perpendicular FCU insertion at 30–40% forearm length, the optimal target is approximately 15 mm anterior to the ulna at a depth of 8 mm, with depth limited to < 13 mm. Although clinical significance of elbow flexion is modest, it remains a practical alternative for patients with contractures or spasticity. To maximize safety, we recommend an oblique approach with insertion approximately 23 mm anterior to ulna, 11 mm deep, at a 45° anterior angle.

(RS-2025-00532972)