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E1261. Preoperative Sonographic Ulnar Nerve Mapping in the Postoperative Elbow
Authors
  1. Garret Powell; Mayo Clinic
  2. Francis Baffour; Mayo Clinic
  3. Michael Moynagh; Mayo Clinic
  4. John Skinner; Mayo Clinic
  5. Tiffany Keller-Lam; Mayo Clinic
  6. Shawn O'Driscoll; Mayo Clinic
  7. Katrina Glazebrook; Mayo Clinic
Background
Elbow arthroscopic and open surgery can be technically challenging in a postoperative elbow. Successful joint access and arthroscopic portal placement is of a higher degree of complexity compared to other joints and suboptimal technique may result in iatrogenic peripheral nerve injury (1-3). During elbow arthroscopy, the ulnar nerve is most susceptible to injury, accounting for 38-42% of all nerve injuries (4, 5). A variant ulnar nerve path (e.g. transposition and subluxation) was historically a contraindication to arthroscopy due to the increased risk of iatrogenic injury (6-9). While operative reports may detail the path of the transposed nerve, these are not always available. Ulnar nerve palpation can facilitate safe portal placement (9, 10); however, this technique is only accurate proximal to the medial epicondyle (5). We describe a technique of sonographic ulnar nerve mapping for preoperative planning in the setting of prior orthopedic elbow surgery and review the use of this technique in our practice.

Educational Goals / Teaching Points
Understand a technique of sonographic ulnar nerve mapping for preoperative planning in the setting of orthopedic elbow surgery. Describe postoperative complications and limitations in the setting of preoperative ulnar nerve mapping.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The patient is placed supine or in a half lateral decubitus position and rolled toward the operator. With a neutral elbow position, the arm is externally rotated and slightly flexed with or without arm abduction depending on the proceduralist’s body position and accessibility to the medial elbow. The patient’s outstretched arm either rests on the bed or on a sheet over the proceduralist’s knees. The ulnar nerve is identified from the level of the mid humerus to the mid forearm using a 8-18.0 MHz linear transducer. Morphological features of the ulnar nerve are recorded and a dynamic evaluation is performed if requested or clinically relevant. The forearm is surveyed for denervation change and the patient is monitored for Tinel’s-like symptoms during the examination. With the transducer in the transverse plane and the ulnar nerve centered in the image, the path of the ulnar nerve about the elbow is then traced on the skin with an indelible surgical marker. The medial epicondyle is also marked and serves as a fixed anatomic reference. A clinical photograph of the nerve path is taken and recorded in the electronic medical record. In a cohort of 24 patients, preoperative sonographic ulnar nerve mapping occurred following various elbow surgeries. Subsequent surgery was performed arthroscopically in 14 and open in 10 cases. In 11 of the 24 cases, there was a modified approach to joint access which was guided by the ulnar nerve map. There were no perioperative ulnar nerve related complications.

Conclusion
Preoperative mapping can facilitate planning of surgical access and ulnar nerve dissection. Sonographic mapping of the ulnar nerve reduces the potential uncertainty of nerve palpation in a complex postoperative elbow. This technique may mitigate the risk of ulnar nerve injury.