Abstract
To present a technical note on how to perform upper extremity peripheral nerve stimulators for three major nerves: median, ulnar, and radial.
Literature review and expert opinion.
Single academic center.
Peripheral nerve stimulation has recently become popular with the development and availability of peripheral nerve stimulators with an external pulse generator. Here, we describe ultrasound anatomy and technical details for peripheral nerve stimulation in the upper extremity for three major nerves: median, ulnar, and radial.
Upper extremity peripheral nerve stimulation can be considered as an option for refractory neuropathic upper extremity pain.
Introduction
Neuromodulation is becoming more prominent in the arsenal of pain-relieving tools that an interventional pain physician can use to treat refractory pain in the extremities. Many providers are proficient with spinal cord stimulation but less familiar with peripheral nerve stimulator (PNS) implantation techniques. Basic principles of median, ulnar, and radial nerve PNS implantation are described.
General Guidelines
Patient selection is crucial to optimizing success with PNS. A detailed history and physical exam will help to assess which peripheral nerve or nerves should be targeted, as well as the actual location of the implant. It is recommended that sonographic evaluation be performed in the office setting before scheduling the procedure to evaluate the trajectory, accessibility, and depth of the nerve. In patients with thin body habitus, targeting a superficial nerve will increase risk of eroding through the skin. Conversely, in an obese patient, both accurate visualization of the nerve and implantation of the PNS may be more challenging. A diagnostic peripheral nerve block may also be useful before scheduling the procedure. Some manufacturers allow for a trial before placing the permanent implant, while some devices are designed to be temporary for up to 60 days.
In the authors’ experience, it is helpful to map the trajectory of the nerve on the skin with a skin marker and note the nerve depth as it changes along the trajectory before insertion of the PNS. Both short- and long-axis views obtained by ultrasonography are helpful in achieving this. It is also helpful to approximate the length and trajectory of the stimulator lead by first laying the lead on top of the extremity. The lead should not cross any joints (to minimize lead migration) and should avoid going through big muscles if possible (to reduce discomfort and unwanted motor stimulation). The orientation and distance of the PNS from the nerve should be according to the manufacturer instructions for the specific device being used. Finally, the lead is secured for a trial or tunneled for implant. Potential risks include lead migration/fracture, skin erosion, damage to the lead, infection, and bleeding.
Median Nerve
Anatomy
The median nerve originates from the lateral cord of the C5-7 roots and the medial cord of C8-T1 roots. It lies anterior and superior to the axillary artery in the axilla and then travels along the inferior aspect of the brachial artery in the anterior compartment of the arm. It lies medial to the brachial artery closer to the antecubital fossa (Figure 1). It then enters the forearm and travels between the two heads of the pronator teres. It can then be found between the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) in the volar aspect of the forearm (Supplementary Data). At this point, it gives off the anterior interosseous nerve (motor), which supplies the deep flexor muscles and the palmar cutaneous nerve (sensory), which supplies the lateral palm. The median nerve becomes superficial as it courses around the lateral edge of the FDS, ∼3–5 cm proximal to the flexor retinaculum (Supplementary Data). As it nears the carpal tunnel, the median nerve can be found between the FDS, flexor carpi radialis (FCR), and flexor pollicis longus tendons. It then passes into the carpal tunnel, deep to the flexor retinaculum [1]. Here it terminates into the recurrent branch (motor), which supplies thenar muscles and palmar digital branches, which supply the palmar surface and fingertips of the three and a half most radial digits (digital cutaneous branches) and two lumbrical muscles. A bifid median nerve occurs frequently in carpal tunnel syndrome due to its relatively larger cross-sectional area compared with a nonbifid median nerve [2]. A persistent median artery within the carpal tunnel is another anatomic variant that should be noted [3–6].
Median nerve above the elbow.
Sonographic Evaluation and PNS Placement
For median nerve PNS placement proximal to the elbow, the patient should be positioned supine with the shoulder abducted to 90º. Next, identify the median nerve in the medial aspect of the arm. It can be identified in short axis as it travels antero-superior to the axillary artery in the axilla and then traced down. The authors recommend inserting the needle proximally to distally at this location if laying the PNS parallel to the nerve, so as to avoid injury to the axillary artery.
For median nerve PNS placement distal to the elbow, the patient should be positioned with the forearm supinated with the wrist in slight dorsiflexion. The median nerve should be identified under ultrasound in the antecubital fossa medial to the brachial artery (Figure 1) and traced distally as it travels through the heads of the pronator teres, and then to the carpal tunnel (Supplementary Data) [6].
The authors recommend inserting the PNS needle proximally to distally (if going parallel to the nerve) along the path of the median nerve, away from the brachial artery (Supplementary Data).
Ulnar Nerve
Anatomy
The ulnar nerve originates from the C8-T1 nerve roots and the medial cord of the brachial plexus. It travels posterior to the brachial artery and median nerve in the medial aspect of the arm. It then travels superficial to the medial head of the triceps brachii and around the posterior aspect of the medial epicondyle and superior ulnar collateral artery (Supplementary Data). It goes through the cubital tunnel and enters the forearm in between the humeral and ulnar heads of the flexor carpi ulnaris (FCU). In the forearm, the ulnar nerve travels between the FDP and FCU muscles (Figure 2). Further distal in the forearm, it lies medial to the ulnar artery (Supplementary Data) and then passes superficial to the flexor retinaculum at the wrist. The ulnar nerve gives off two sensory branches in the forearm—the palmar cutaneous branch, which supplies the medial half of the palm, and dorsal cutaneous branch, which innervates the dorsal surface of the medial one and a half fingers, and the associated dorsal area of the hand. It enters the hand via Guyon’s canal and terminates in superficial sensory and deep motor branches. The superficial branch supplies the palmar surface of the medial one and a half fingers [4–6].
Ulnar nerve in the forearm.
Sonographic Evaluation and PNS Placement
Similar to the median nerve, the ulnar nerve PNS can be placed either in the upper arm or in the forearm. For placement in the upper arm, the patient should be positioned supine with the shoulder abducted to 90º and the elbow flexed to 90º (Supplementary Data). For placement in the forearm, the patient should be positioned with the forearm supinated and the wrist in slight dorsiflexion. In the authors’ experience, it is easiest to identify the nerve at the wrist in close proximity to the ulnar artery (Supplementary Data) and then trace up the forearm (Figure 2) as it enters the cubital tunnel (Supplementary Data). The authors recommend inserting the PNS needle distally to proximally to avoid injury to the ulnar artery, if inserting the PNS parallel to the nerve in the forearm (Supplementary Data).
Radial Nerve
Anatomy
The radial nerve originates from the ventral rami of C5–T1 and forms part of the posterior cord of the brachial plexus. The axillary artery runs anterior to the nerve. The nerve then travels within the axilla and passes anterior to the posterior wall of the axilla, formed by the subscapularis, latissimus dorsi, and teres major [7]. In the upper arm, the radial nerve can be identified as it arises lateral to the long head of triceps brachii muscle. It courses laterally, descending between the medial and lateral heads of the triceps brachii. It gives off three branches in the axilla: the posterior cutaneous nerve of the arm, a branch to the long head of the triceps, and a branch to the medial head of the triceps. The posterior cutaneous nerve of the arm supplies a portion of the posterior aspect of the arm. It then travels within the spiral groove of the humerus, between the lateral and medial heads of the triceps (Supplementary Data). The radial nerve gives off four branches within the spiral groove: the inferior lateral cutaneous nerve of the arm, the posterior cutaneous nerve of the forearm, the branch to the lateral head of the triceps, and the branch to the medial head of the triceps and anconeus. The posterior cutaneous nerve of the forearm supplies a portion of the posterior aspect of the forearm. It then passes through the lateral intermuscular septa and runs in between the brachialis and brachioradialis, anterior to the lateral epicondyle (Figure 3). Here, it gives off motor branches to supply the lateral brachialis, brachioradialis, and extensor muscles of the hand (extensor carpi radialis longus and extensor carpi radialis brevis). As the radial nerve enters the forearm, it divides into the posterior interosseous nerve (deep branch) and the superficial, sensory, radial nerve [8] (Supplementary Data). The superficial branch travels along the radial artery (Supplementary Data) and provides sensory supply to the dorsum of the wrist and the dorsal aspects of part of the thumb, index, and middle finger. The deep branch supplies the extensors of the forearm [4, 5].
Radial nerve in the intermuscular septum.
Sonographic Evaluation and PNS Placement
For placement of the PNS in the upper arm, the arm should be internally rotated, with elbows flexed at 90º (hand on the patient’s belly). The radial nerve is easiest to identify in the arm within the spiral groove, close to the humerus and 10–15 cm from the olecranon process (Supplementary Data). For radial nerve PNS placement distal to the elbow, the patient should be positioned with the forearm supinated with the wrist in slight extension, similar to the positioning for the median and ulnar nerves.
Sample Cases
The first case is a 38-year-old male who presented with pain in the palmar aspect of the right hands secondary to human papillomavirus papillomatosis that was refractory to medication, cryoablation, curetting, and antifungal injection. After a successful test block, he underwent a median nerve PNS trial and implant, which resulted in 80% pain relief (ongoing at one-year follow-up) and significantly improved function (Figure 4).
Ultrasound image of peripheral nerve stimulator.
The second case is a 75-year-old male with refractory left arm pain and tingling secondary to left carpal tunnel and cubital tunnel syndrome who had failed surgery. After a successful test block, he then underwent median and ulnar nerve PNS trial, followed by implantation, which resulted in 85% pain relief and improvements in function (Figure 5). At one-year follow-up, he reported overall 50% pain relief.
Fluoroscopic images of median and ulnar nerve peripheral nerve stimulation.
Funding sources: Dr. Singh’s participation was supported in part by the National Center for Advancing Translational Sciences of the National Institutes of Health under Award number UL1TR002378 and KL2TR002381. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Conflicts of interest: None.
Supplement sponsorship: This article appears as part of the supplement entitled “Peripheral Nerve Stimulation: Update for the 21st Century” sponsored by Bioness and by SPR Therapeutics, Inc.
