The posterior root-muscle reflex

Abstract Posterior root-muscle (PRM) reflexes are short-latency spinal reflexes evoked by the electrical stimulation of large-diameter proprioceptive fibers within the lumbar and upper sacral posterior roots. PRM reflexes share key physiological characteristics with the H-reflex but can be simultaneously evoked in all major lower limb muscle groups bilaterally by a single stimulus pulse. In this chapter, we will discuss the history of studies of PRM reflexes, the relevant neuroanatomy, methodological aspects of evoking PRM reflexes by epidural and transcutaneous spinal cord stimulation, and their electromyographic and physiological characteristics, specifically in comparison to the H-reflex. We will give two examples of the use of PRM reflexes in intraoperative monitoring, first, to guide accurate epidural lead placement over the lumbosacral spinal cord segments for the improvement of lower limb motor function in individuals with spinal cord injury, and second, for the early warning of nerve injuries during complex hip surgeries.