The H-Reflex and F-Response

Abstract

Common electrophysiological recording modalities applied in the surgical setting include somatosensory evoked potentials (SSEPs), motor evoked potentials (TcMEPs), and electromyography (EMG). Central function is traditionally monitored with SSEPs and TcMEPs. Spinal nerve and nerve root function can be more easily assessed with EMG. While generally accepted to provide complete spinal cord protection, SSEPs are specific for the dorsal white matter tracts and the vascular territory of the posterior spinal arteries. The TcMEP is specific for monitoring descending white matter pathways of the lateral and anterior columns, but is also distinct in being the only routinely applied modality to monitor the integrity of the spinal gray matter. While useful in detecting gross changes in motor function as a result of spinal cord injury, TcMEPs do not monitor more complex spinal circuits including multisegmental, interneuronal, and propriospinal circuitry responsible for the control of voluntary movement. Furthermore, TcMEP monitoring has some contraindications and typically causes considerable patient movement and the risk of bite injury. Two other modalities, the Hoffmann reflex (H-reflex) and the F-response, have been proposed as valuable adjuncts to SSEPs and TcMEPs for monitoring spinal cord integrity during neurosurgical spine procedures [1].