Cryoneurolysis for the Forearm in Spasticity Management

The ulnar and median nerves innervate important muscles, frequently involved in upper limb spasticity, patterns, including the clenched fist, thumb in palm, wrist flexion, and forearm pronation. Nerve-targeted procedures, including diagnostic nerve block (DNB) and cryoneurolysis, are increasingly used in spasticity management. Percutaneous cryoneurolysis is a minimally invasive, ultrasound-guided procedure recently utilized as a novel treatment for spasticity.1 Winston et al. have shown that cryoneurolysis can provide long-lasting changes in spasticity measurements and function, reduce pain, and improve participants’ satisfaction.1 Unlike phenol and alcohol, cryoneurolysis is often targeted directly at sensory and mixed-sensorimotor nerves, and being drug-free has unlimited targets for a patient, provided the DNB found no unwanted sensory disturbances.1–3 This video gallery demonstrates ultrasound-guided DNB and cryoneurolysis. Ultrasound allows for direct visualization of the nerve trunks, their individual branches, and those within the muscles.2 The addition of electrical stimulation maximizes the precise identification of these targets.2 The use of a linear transducer in the transverse axis is recommended. Locating blood vessels also helps identify the adjacent nerve branches, as seen in the video, https://links.lww.com/PHM/C782.3 Understanding the anatomy is crucial to localizing the nerves and their branches and avoiding the blood vessels.1 The following is a brief discussion regarding the relevant anatomy of the median and ulnar nerves, focusing on the forearm. The median nerve is formed by the union of the medial and lateral roots of the brachial plexus. The nerve descends from lateral to the brachial artery proximally to its medial side at the elbow. Below the cubital fossa, it passes between the two heads of pronator teres and then deep to the flexor digitorum superficialis. Near the elbow, the median nerve gives muscular branches, first to the pronator teres and then to the flexor carpi radialis, palmaris longus, and flexor digitorum superficialis (Fig. 1A). Distal to the pronator teres, the anterior interosseous membrane branches from the median nerve and gives off branches to the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. Distally, the median nerve provides sensory branches and motor innervation to the thenar muscles.1FIGURE 1: A, Ultrasound image of the forearm flexors below the elbow innervated by the median nerve. B, The ultrasound image of the flexor carpi ulnaris with the mixed sensorimotor ulnar nerve trunk below.The ulnar nerve originates from the medial cord of the brachial plexus. In the arm, it runs close to the brachial vessels in the flexor compartment before traveling to the extensor compartment in the lower third of the arm. The ulnar nerve gives off no branches in the arm. The nerve then passes posterior to the medial epicondyle. It enters the forearm, passing between the humeral and ulnar heads of flexor carpi ulnaris, before it travels between the flexor carpi ulnaris and the flexor digitorum profundus muscles. Just distal to the cubital tunnel, the nerve gives off the first motor branch to the flexor carpi ulnaris (Fig. 1B) and then to the flexor digitorum profundus to the fourth and fifth digits. It is important to note that the ulnar artery lies on the lateral side of the ulnar nerve in the distal two-thirds of the forearm. Distally, the ulnar nerve provides sensory branches to the hand and motor innervation to most hand-intrinsic muscles.1