Ultrasound Guidance to Augment Needle Electromyography Precision in the Complex Nerve Injury Setting

The rise in popularity of nerve transfer surgery in individuals with peripheral nerve and spinal cord injuries has elevated the importance of the preoperative electrodiagnostic examination. Needle electromyography (EMG) provides peripheral nerve surgeons with precise information about donor and recipient muscle health, aiding in decisions regarding surgical options, donor muscle viability, and timing of intervention. However, traditional anatomical landmarks for typical donor and recipient nerve-muscle combinations in nerve transfer surgery are either not well described in the literature or become less dependable in the presence of contracture, spasticity, or muscle atrophy and fibrosis. Ultrasound (US) can be a valuable tool to augment the needle EMG examination. Herein, we describe US approaches to improve the precision of the needle EMG examination for 10 muscles in the upper extremity and two muscles in the lower extremity that are routinely involved as either donors or recipients in nerve transfer surgery. The purpose is to provide a reference guide for the electrodiagnostic medicine specialist in the complex nerve injury setting. This includes information on surrounding anatomical structures for localization and those that should be avoided. Relevant US principles for EMG are discussed including: (1) the advantages and disadvantages of short-axis and long-axis views of the target muscle, emphasizing the predominant use of short-axis for adequate visualization of all surrounding structures and enhancing patient safety, (2) in-plane versus out-of-plane approaches, and (3) enhancing confidence in the precision of the needle EMG via the dynamic capability of US.