Sensory neurotization of muscle: past, present and future considerations

Sensory nerve regeneration and reinnervation in muscle following peripheral nerve injury

Sensory afferent fibers are an important component of motor nerves and compose the majority of axons in many nerves traditionally thought of as "pure" motor nerves. These sensory afferent fibers innervate special sensory end organs in muscle, including muscle spindles that respond to changes in muscle length and Golgi tendons that detect muscle tension. Both play a major role in proprioception, sensorimotor extremity control feedback, and force regulation. After peripheral nerve injury, there is histological and electrophysiological evidence that sensory afferents can reinnervate muscle, including muscle that was not the nerve's original target. Reinnervation can occur after different nerve injury and muscle models, including muscle graft, crush, and transection injuries, and occurs in a nonspecific manner, allowing for cross-innervation to occur. Evidence of cross-innervation includes the following: muscle spindle and Golgi tendon afferent-receptor mismatch, vagal sensory fiber reinnervation of muscle, and cutaneous afferent reinnervation of muscle spindle or Golgi tendons. There are several notable clinical applications of sensory reinnervation and cross-reinnervation of muscle, including restoration of optimal motor control after peripheral nerve repair, flap sensation, sensory protection of denervated muscle, neuroma treatment and prevention, and facilitation of prosthetic sensorimotor control. This review focuses on sensory nerve regeneration and reinnervation in muscle, and the clinical applications of this phenomena. Understanding the physiology and limitations of sensory nerve regeneration and reinnervation in muscle may ultimately facilitate improvement of its clinical applications.

Direct Neurotization: Past, Present, and Future Considerations

ABSTRACT

Direct neurotization is a method that involves direct implantation of nerve fascicles into a target tissue, that is, muscle fibers, skin, cornea, and so on, with the goal of restoring aesthetic, sensation and or functional capacity. This technique has been implemented since the early 1900s, with numerous experimental and clinical reports of success. Applications have included both sensory and motor neurotization of muscle, as well as protective sensory provision for other organs. These techniques have been used to restore corneal sensation, repair brachial plexus injuries, reestablish tongue movement and function through direct tongue neurotization, and reinnervate multiple facial muscles in patients with facial paralysis. Most recently, these methods have even been used in conjunction with acellular cadaveric nerve grafts to directly neurotize skin. Indications for direct neurotization remain limited, including those in which neural coaptation is not feasible (ie, surgical or traumatic damage to neuromuscular junction, severe avulsion injuries of the distal nerve); however, the success and wide-range application of direct neurotization shows its potential to be implemented as an adjunct treatment in contrast to views that it should solely be used as a salvage therapy. The purpose of the following review is to detail the historic and current applications of direct neurotization and describe the future areas of investigation and development of this technique.

Regenerative Peripheral Nerve Interfaces for the Management of Symptomatic Hand and Digital Neuromas

Painful neuromas result from traumatic injuries of the hand and digits and cause substantial physical disability, psychological distress, and decreased quality of life among affected patients. The regenerative peripheral nerve interface (RPNI) is a novel surgical technique that involves implanting the divided end of a peripheral nerve into a free muscle graft for the purposes of mitigating neuroma formation and facilitating prosthetic limb control. The RPNI is effective in treating and preventing neuroma pain in major extremity amputations. The purpose of this study was to determine if RPNIs can be used to effectively treat neuroma pain following partial hand and digital amputations. We retrospectively reviewed the use of RPNI to treat symptomatic hand and digital neuromas at our institutions. Between November 2014 and July 2019, we performed 30 therapeutic RPNIs on 14 symptomatic neuroma patients. The average patient follow-up was 37 weeks (6-128 weeks); 85% of patients were pain-free or considerably improved at the last office visit. The RPNI can serve as a safe and effective surgical solution to treat symptomatic neuromas after hand trauma.