Ultrasound-Guided Steroid Injections for Lateral Antebrachial Cutaneous Nerve Entrapment Within Post-Surgical Scar

Abstract

A 26-yr-old man experienced a motorbike accident and underwent open reduction and internal fixation of a right humerus and radio-ulnar shaft fractures the next day. Nerve conduction studies were performed 3 mos later because of sensorimotor symptoms in his right upper limb and confirmed axillary, musculocutaneous, and radial neuropathies at the level of the axilla. Because of persistent elbow flexion weakness (manual muscle testing grade 3), surgical excision and advance flap of a longitudinal hypertrophic scar extending from the shoulder to the upper arm were performed. He also eventually underwent removal of the orthopedic implants. He then started rehabilitation focused on range of motion and strengthening exercises of his right upper limb. Function and strength improved gradually, and he returned to work after 1 yr. However, right lateral forearm tightness and numbness were interfering with his daily activities and with sleep. Ultrasonographic (US) tracking of his lateral antebrachial cutaneous nerve (LABCN) showed focal swelling within the forearm scar. Ultrasound-guided hydrodissection of the LABCN with 5 mL of 5% dextrose water was attempted. The symptoms improved by 50% after the procedure but recurred 1 mo later. Therefore, the same procedure was performed a second time 2 mos later, and the symptoms were relieved completely for 1 mo. A third US-guided hydrodissection of the LABCN was performed, but the injectate was changed to triamcinolone 10 mg and 5 mL of lidocaine 1% (Video 1). The patient remained symptom free at the 6-mo follow-up. The LABCN is a terminal branch of musculocutaneous nerve, which is responsible for sensation of the lateral aspect of the forearm. It lies adjacent to the cephalic vein and the distal biceps brachii tendon within the antebrachial region of the elbow, and compression of the LABCN typically presents as pain and dysesthesia along the lateral forearm.1 Common causes of LABCN neuropathy include cephalic venipuncture, distal biceps brachii tendon tears and repair, and pull-up exercises during military training camp.1 This is the first reported case in the literature of LABCN entrapment within a surgical scar. Although electrophysiological studies can determine the level and type of nerve lesion, US nerve tracking may be used to evaluate the cause, severity, and etiology of the entrapment.2 In this case, nerve conduction studies showed slowed sensory nerve conduction velocity and reduced sensory nerve action potential amplitude in the right LABCN. Ultrasound further identified entrapment level and confirmed the cause, which provided a path for potential treatments. Ultrasound-guided nerve hydrodissection is commonly used in pain management although high-quality evidence of its effects is still lacking.3 In this case, the entrapped site was close to the radial artery. Ultrasound guidance prevented unintended injury to the artery. For safety concern, dextrose water is advocated as the primary regimen by more and more physicians for perineural injections. In this case, dextrose was initially used but the effect lasted only for 1 mo. In those whose nerve is entrapped within a scar, corticosteroid may be an alternative if dextrose fails. In conclusion, US is a useful tool to identify morphological changes of peripheral nerves and surrounding structures and is helpful to guide procedures.