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Ultrasound Guided Nerve Block

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Illustration 1: Distribution of sensory innervation, anterior.

Illustration 2:  Distribution of sensory innervation, posterior.

Figure 1:  Picture of patient set-up, probe and needle position with in-line approach.

Figure 2:  Still image of the ulnar nerve at the level of the wrist. 

Figure 3: Sonographic image of the ulnar nerve at the mid-forearm.

Video clip 1:  Video clip of ulnar nerve block at mid-forearm.

Figure 4:  Image of the probe and needle position for ulnar nerve block at the mid-forearm.

Figure 5: Image of the probe and needle position for ulnar nerve block at the cubital fossa.

Figure 6: Sonographic appearance of ulnar nerve at the cubital fossa.

Figure 7: Image of the patient set-up and probe and needle position for ulnar nerve block at the distal humerus.

Figure 8:Sonographic appearance of ulnar nerve at the distal humerus.

Video 2: Ulnar nerve block above elbow.

Video 3: Ulnar nerve block above elbow with out-of-plane approach.


Leonard V. Bunting, M.D.; and Beatrice Hoffmann, M.D., Ph.D., RDMS

Ulnar Nerve Block

Anatomy

The ulnar nerve originates from the C8-T1 nerve roots, which form parts of the medial cord of the brachial plexus.  It is a mixed sensory and motor nerve and provides sensory innervation to the medial aspect of the hand.  It descends on the posteromedial aspect of the humerus and enters the flexor compartment of the forearm by passing between the olecranon and medial epicondyle of the humerus (“cubital tunnel”) and through the two heads of the flexor carpi ulnaris.  The nerve then travels near the ulnar bone and medial to the ulnar artery in the distal forearm.  About 5 to 10 cm proximal to the wrist dorsal and palmar cutaneous branches split and provides innervation to the medial aspect of the hand.  Artery and nerve are found deep to the tendon of the flexor carpi ulnaris and enter the palm superficial to the flexor retinaculum, via the ulnar canal.


Illustration 1: Distribution of sensory innervation, anterior.



Illustration 2:  Distribution of sensory innervation, posterior.


The ulnar nerve can be blocked at the level of the wrist, the mid-forearm, and proximal to or at the level of the elbow.

Scanning Techniques and Nerve Blocks

Ulnar Nerve Block at the Wrist

In the wrist, the hyperechoic appearing ulnar nerve lies medially, adjacent to the artery.  The conventional method of nerve blockage at the wrist relies on anatomical landmarks, which can also be located sonographically.  The nerve is located between the ulnar artery and the flexor carpi ulnaris at the level of the proximal volar skin crease. This approach can spare the dorsal and volar sensory branches of the ulnar nerve, which arises earlier in the course of the nerve, about 5 cm proximal to the wrist.
A high-frequency (10-18 MHz), linear array probe is used with appropriate depth adjustment. Under sonographic guidance, the ulnar artery is located and the nerve can be found medial.  The needle is preferably inserted in an in-plane orientation, very slowly, from the ulnar aspect of the transducer.  This allows continuous visualization of the needle along its entire length. About 3-5 cc of local anesthetic is injected and paresthesia should occur within 5-15 minutes. (1-4)



Figure 1:  Picture of patient set-up, probe and needle position with in-line approach.



Figure 2:  Still image of the ulnar nerve at the level of the wrist. 



Ulnar Nerve Block – Forearm
To locate the ulnar nerve in the forearm, one can trace the artery proximally until the nerve becomes visible in the mid-forearm located medial to the vessel.  Some investigators feel that ultrasound-guided blockage of the ulnar nerve is easiest at this location.(1) Here, the ulnar artery, which is in close proximity to the nerve, facilitates sonographic detection but is starting to move away from the nerve, potentially reducing the risk of arterial puncture.  Blockade at this level may also improve chances of providing anesthesia of the dorsal and volar sensory branches of the ulnar nerve, which branch out about 5 cm above the wrist.(2)



Figure 3: Sonographic image of the ulnar nerve at the mid-forearm.


Video clip 1:  Video clip of ulnar nerve block at mid-forearm.

A high-frequency (10-18 MHz), linear array probe is used with appropriate depth adjustment. The needle is preferably inserted in an in-plane orientation, from the ulnar aspect of the transducer.  This allows continuous visualization of the needle along its entire length. About 3-5 cc of local anesthetic is injected and paresthesia should occur within 5-15 minutes.



Figure 4:  Image of the probe and needle position for ulnar nerve block at the mid-forearm.



Ulnar Nerve Block – Elbow
In the absence of ulnar nerve dislocation, the ulnar nerve lies in the cubital tunnel on the medial aspect of the elbow. The ulnar nerve can be easily located in the groove between the olecranon and the medial epicondyle.  The probe orientation should be transverse and needle orientation in-plane.



Figure 5: Image of the probe and needle position for ulnar nerve block at the cubital fossa.

 



Figure 6: Sonographic appearance of ulnar nerve at the cubital fossa.



However, It is postulated that the ulnar nerve can be compressed in the poorly compliant cubital tunnel by large volumes of local anesthetic. Therefore, injections at this site should be limited to 3-5 cc’s to minimize the risk of a compartment syndrome. To avoid this risk completely, the ulnar nerve can be blocked a several centimeters above the elbow. The nerve is identified in the cubital tunnel and traced proximally into the distal or mid-upper arm. At this site the nerve is superficial and surrounded by soft tissue.



Figure 7: Image of the patient set-up and probe and needle position for ulnar nerve block at the distal humerus.

 



Figure 8: Sonographic appearance of ulnar nerve at the distal humerus.


A high-frequency (10-18 MHz), linear array probe is used with appropriate depth adjustment. The needle is preferably inserted in an in-plane orientation, from the ulnar aspect of the transducer.  This allows continuous visualization of the needle along its entire length. About 3-5 cc of local anesthetic is injected and paresthesia should occur within 5-15 minutes.



Video 2: Ulnar nerve block above elbow.

 


Video 3:
Ulnar nerve block above elbow with out-of-plane approach.

Pearls and Pitfalls

When using an out-of-plane approach, injecting small amounts of anesthetic can help localizing the needle tip.
A convenient location for blockade of the ulnar nerve is the mid-forearm.  This location combines the ease of visualization, ability to block all terminal branches and minimal potential for vascular injury.

A superficial ulnar artery may join the ulnar nerve as distal as the wrist and complicate anatomical orientation. (1)

References

1. McCartney CJ, Xu D, Constantinescu C, Abbas S, Chan VW.
Ultrasound examination of peripheral nerves in the forearm. Reg Anesth Pain Med. 2007;32(5):434-9. Erratum in: Reg Anesth Pain Med. 2008;33(2):188.

2.  Gray AT, Schafhalter-Zoppth I.
Ultrasound guidance for ulnar nerve block in the forearm. Reg Anesth Pain Med., 2003;28:335-339.

3. Loewy J.
Sonoanatomy of the median, ulnar and radial nerves. Can Assoc Radiol J. 2002;53(1):33-8. Review.

4. Kathirgamanathan A, French J, Foxall GL, Hardman JG, Bedforth NM.
Delineation of distal ulnar nerve anatomy using ultrasound in volunteers to identify an optimum approach for neural blockade. Eur J Anaesthesiol. 2009;26(1):43-6.

 


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