Trick of the Trade: Patient positioning for ultrasound-guided ulnar nerve block

Patients with 5th metacarpal fractures (commonly termed “boxer’s fracture”) are frequently treated in the emergency department (ED) with closed reduction and splinting. Obtaining analgesia and a successful closed reduction can often be challenging without procedural sedation. Severe swelling can make a hematoma block difficult, often resulting in inadequate analgesia. An ultrasound-guided ulnar nerve block provides a simple method to facilitate pain relief and allow for improved fracture site manipulation.

Standard ultrasound-guided ulnar nerve block technique

Using a high frequency (10-5 MHz) linear transducer in a transverse plane, the ulnar nerve can be seen separating (in a medial direction) from the ulnar artery in the proximal forearm.

 

With clear needle visualization, 3-5 cc of anesthetic (lidocaine 1-2% or bupivicaine 0.25%) should be precisely deposited in the fascial plane surrounding the ulnar nerve. The in-plane needle technique allows the novice sonographer an easy target with clear needle visualization. Unfortunately, because of the very medial position of the ulnar nerve, patients are often unable to hypersupinate their forearm in a manner that allows for the in-plane needle technique to be performed.

For the advanced sonographer who is comfortable with ultrasound-guidance for nerve blocks, the out-of-plane technique is commonly favored when performing the ulnar nerve block. This technique does not afford needle visualization, and in our experience has been very difficult the novice provider. We developed a novel patient position for the in-plane ultrasound-guided ulnar nerve block to allow for patient comfort and a clear view of the needle for the operator.

Pearl: Along with analgesia for 5th metacarpal fractures, the ultrasound-guided ulnar nerve block at the forearm can be used for lacerations, burns and other injuries that are located on the ulnar aspect of the hand. Only perform this (and any block) after a well-documented neurovascular exam has been performed.

Trick of the Trade: Alternative patient positioning for ultrasound-guided ulnar nerve block

1. Place the patient in the supine position on the gurney. Elevate the head of the bed approximately 45 degrees.
2. Abduct the affected extremity and place the forearm on a stable surface (pic 2A).
3. Flex at the elbow to 90 degrees and support the extremity with a stack of towels posteriorly. (pic 2B).

 

4. Place the ultrasound screen opposite the provider to allow for a clear view of the injection site and the ultrasound screen.

Anesthetic and needle selection

We recommend using 3-5 cc of lidocaine 1-2% until the provider is comfortable with clear needle visualization. Bupivicaine is more commonly associated with local anesthetic systemic toxicity (LAST) and should be used with caution for injections near vascular structures. Intravenous lipid emulsion therapy should be available for any provider who is using either lidocaine or bupivicaine for nerve blocks as a treatment for local anesthetic toxicity [1]. A standard 1.5 inch 25-gauge needle (or 22 gauge blunt-tipped regional block needle if available) will be adequate for this block. (NOTE: For demonstration purposes, a larger and more easily visualized spinal needle is being used in the above images).

Conclusion

Ultrasound-guided nerve block of the ulnar nerve is a useful technique for emergency physicians to use for hand injuries that involve the posterior and ulnar aspects of the hand. Additionally, ulnar nerve blockade may be ideal for reduction of 5th metacarpal fractures (boxer’s fracture). Using our novel alternative patient positioning for the in-plane ultrasound-guided ulnar nerve block, more novice operators can easily integrate this technique into clinical practice. In our experience, the in-plane ultrasound-guided ulnar nerve block has been an extremely useful procedure in the clinical department, improving patient comfort while negating the need for resource intensive procedural sedation.

 

References

1. Weinberg, G. Lipid Emulsion Infusion: Resuscitation for Local Anesthetic and other Drug Overdose. Anesthesiology Jul 2012; 117(1): 180-187.

Additional Reading

1. Gray AT. Ulnar Nerve Block. Atlas of Ultrasound-Guided Regional Anesthesia: Expert Consult 2012;133-4.
2. Liebmann O, Price D, Mills C, et al. Feasibility of forearm ultrasonography-guided nerve blocks of the radial, ulnar, and median nerves for hand procedures in the emergency department. Ann Emerg Med. 2006; 48(5): 558-62. PMID: 17052557
3. Sohoni A, Herring A, Stone M, Nagdev A. Focus On: Ultrasound-Guided Forearm Nerve Blocks. ACEP News. October 2011.

 

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