Radial nerve anesthesia rests upon disrupting impulse conduction in the nerve with drugs such as local anesthetics that can be given locally to block specific nerves and can be reversed as needed. Disrupting nerve impulse conduction can be done at any region of the body where nerves are easily accessible for visualization and injection. A radial nerve block will provide anesthesia and/or analgesia to the hand, specifically the dorsal radial side. This includes anesthesia dorsally to the thumb, index and middle fingers, and the lateral aspect of the ring finger. It can be useful as a stand-alone or adjunctive therapy for interventions of the hands and fingers, palliation of acute pain involving the radial nerve's distribution, diagnosis and treatment of radial tunnel syndrome, as well a diagnostic and prognostication procedure in instances of injury to the radial nerve. This block is especially useful for the clinician as an alternative to procedural sedation and escalating opioid analgesic requirements for acutely painful conditions such as fractures, lacerations, and burns.
The radial nerve, along with the axillary artery, originates as a branch of the brachial plexus, specifically from the posterior cord of the plexus. The nerve is comprised of fibers from C5-T1 spinal roots. Proximally, the radial nerve is found posterior and inferior to the axillary artery. Once it exits the axilla, the nerve descends into the arm by passing anterior to the latissimus dorsi muscle insertion and then passes between the medial and long heads of the triceps muscle to eventually lie on the posterior surface of the humerus. The radial nerve has multiple branches, which include the sensory posterior cutaneous branch of the forearm and the superficial radial nerve, as well as the motor deep radial nerve. The posterior cutaneous branch divides from the radial nerve proximal to the humeral lateral epicondyle, providing sensation to the elbow and the posterior forearm. Continuing distally, the radial nerve courses over the humeral spiral groove and emerges close to the lateral epicondyle. It subsequently pierces the lateral intermuscular septum to arrive at the anterior compartment of the arm, lying in-between the brachialis and brachioradialis muscles. Here, at the level of the antecubital fossa, it divides into its two terminal branches, the superficial and deep branches. The superficial branch is close to the radial artery, responsible for afferent innervation. This is a sensory branch, innervating the geographical area of the wrist dorsally and part of the thumb and index and middle fingers proximal to the DIP dorsally. The deep branch is responsible for motor innervation to the extensors of the forearm.
It is important to understand the anatomical path of the radial nerve as it has significant implications when attempting to achieve an anesthetic block along its course. The ideal locations of the anesthetic block described in the literature include locations above, at, and below the elbow. Above the elbow (above the bifurcation of the radial nerve into its terminal branches), the block can be done a location 4 inches above the humeral lateral epicondyle between the brachialis and brachioradialis muscles. Additionally, the nerve can also be blocked at the level of the elbow in the antecubital fossa prior to the division into its terminal branches. Lastly, the superficial radial nerve can be anesthetized below the elbow at the level of the proximal third of the forearm.
Indications for radial nerve block include:
Contraindications to the radial nerve block include:
For an ultrasound-guided radial nerve block you will need the following:
Properly trained personnel with experience using ultrasound-guided regional anesthesia should perform the procedure with adequate support staff.
After obtaining informed consent, position the patient depending on which approach to the radial nerve block is being attempted as outlined below in the technique section. Subsequently, either povidone-iodine or chlorhexidine 2% can be used to prepare the skin over the site of anesthetic injection. Next, the application of a sterile probe cover to the ultrasound probe is recommended, followed by the application of sterile gel to the intended injection site. Lastly, a local anesthetic is drawn up into a syringe. Ensure appropriate monitoring and access to intralipid 20% in cases of local anesthetic systemic toxicity. 
There are 3 techniques with which to attempt an anesthetic block to the radial nerve.
Proximal Third of the Forearm
An anesthetic block can be performed here before the superficial radial nerve joins the lateral aspect of the radial artery proximal to its division into smaller branches.
At the Elbow in the Antecubital Fossa
An anesthetic block can be performed here at the antecubital fossa before the nerve divides into superficial (sensory) and deep (motor) branches.
Above the Elbow Just Distal to the Humeral Spiral Groove
An anesthetic block can be performed here at the level of the spiral groove on the posterolateral aspect of the humerus to block the deep and superficial branches of the radial nerve.
The use of local peripheral nerve blocks for surgical anesthesia, post-operative pain, acute and chronic pain syndromes, as well as a multitude of other indications has significantly increased with the advent of ultrasound-guided techniques. Furthermore, the use of ultrasound has improved the overall success and efficiency of the peripheral nerve block while minimizing the risk of local anesthetic toxicity.
The utilization of peripheral ultrasound-guided nerve blocks helps to provide a viable alternative to procedural sedation which has potential risks and is both labor and time intensive to both patient and physician. The use of ultrasound has been classified as Level 1b evidence for faster block onset and higher rates of block success by the American Society of Regional Anesthesia and Pain Medicine. An ultrasound-guided radial nerve block, alone or in combination with other treatments, represents a therapeutic resource for treating multiple different varieties of pain and clinical entities.
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