Managing Complex Peripheral Nerve Injuries Within the Military Health System: A Multidisciplinary Approach to Treatment, Education, and Research at Walter Reed National Military Medical Center

Combat-related peripheral nerve injuries

Active-duty service members (ADSM) and military Veterans represent a population with increased occupational risk for nerve injuries sustained both during training operations and wartime. Mechanisms of war-related nerve injuries have evolved over time, from the musket ball-related traumas described by S.W. Mitchell to complex blast injuries and toxic exposures sustained during Middle East conflicts in the 21st century. Commonly encountered nerve injury etiologies in this population currently include compression, direct trauma, nutritional deficits, traumatic limb amputation, toxic chemical exposures, or blast-related injuries. Expeditious identification and comprehensive, interdisciplinary treatment of combat-associated neuropathies, as well as prevention of these injuries whenever possible is critical to reduce chronic morbidity and disability for service members and to maintain a well-prepared military. However, diagnosis of a combat-associated nerve injury may be particularly challenging due to comorbid battlefield injuries or delayed presentation of neuropathy from military toxic exposures. Advances in imaging for nerve injury, including MRI and ultrasound, provide useful tools to compliment EMG in establishing a diagnosis of combat-associated nerve injury, particularly in the setting of anatomic disruption or edema. Surgical techniques can improve pain control or restoration of function. In all cases, comprehensive interdisciplinary rehabilitation provides the best framework for optimization of recovery. Further work is needed to prevent combat-associated nerve injuries and promote nerve recovery following injury.

The Scope and Distribution of Upper Extremity Nerve Injuries Associated With Combat-Related Extremity Limb Salvage

PURPOSE

Chronic pain and functional limitations secondary to nerve injuries are a major barrier to optimal recovery for patients following high-energy extremity trauma. Given the associated skeletal and soft tissue management challenges in the polytraumatized patient, concomitant nerve injuries may be overlooked or managed in delayed fashion. Whereas previous literature has reported rates of peripheral nerve injuries at <10% in the setting of high-energy extremity trauma, in our experience, the incidence of these injuries has been much higher. Thus, we sought to define the incidence, pain sequelae, and functional outcomes following upper extremity peripheral nerve injuries in the combat-related limb salvage population.

METHODS

We performed a retrospective review of all patients who underwent limb salvage procedures to include flap coverage for combat-related upper extremity trauma at a single institution between January 2011 and January 2020. We collected data on patient demographics; perioperative complications; location of nerve injuries; surgical interventions; chronic pain; and subjective, patient-reported functional limitations.

RESULTS

A total of 45 patients underwent flap procedures on 49 upper extremities following combat-related trauma. All patients were male with a median age of 27 years, and 96% (n = 47) of injuries were sustained from a blast mechanism. Thirty-three of the 49 extremities (67%) sustained associated nerve injuries. The most commonly injured nerve was the ulnar (51%), followed by median (30%) and radial/posterior interosseous (19%). Of the 33 extremities with nerve injuries, 18 (55%) underwent surgical intervention. Nerve repair/reconstruction was the most common procedure (67%), followed by targeted muscle reinnervation (TMR, 17%). Chronic pain and functional limitation were common following nerve injury.

CONCLUSIONS

Upper extremity peripheral nerve injury is common following high-energy combat-related trauma with high rates of chronic pain and functional limitations. Surgeons performing limb salvage procedures to include flap coverage should anticipate associated peripheral nerve injuries and be prepared to repair or reconstruct the injured nerves, when feasible.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Ultrasound-Activated Piezoelectric Polyvinylidene Fluoride-Trifluoroethylene Scaffolds for Tissue Engineering Applications

Severe peripheral nervous system (PNS) injuries have limited options for therapeutic solutions to regain functional recovery. This can be attributed in part to the lack of regeneration pathways promoted by recapitulating chemical, physical, and electrical cues to direct nerve guidance. To address this, we examined ultrasonic stimulation of a piezoelectric polyvinylidene fluoride-triflouroethylene (PVDF-TrFE) scaffold as a potentially clinically relevant therapy for PNS regeneration. Owing to the piezoelectric modality of PVDF-TrFE, we hypothesize that ultrasound stimulation will activate the scaffold to electrically stimulate cells in response to the mechanical deformation mediated by sound waves. Biocompatible PVDF-TrFE scaffolds were fabricated to be used as an ultrasound-activated, piezoelectric biomaterial to enhance cellular activity for PNS applications. NIH-3T3 fibroblasts were cultured on PVDF-TrFE nanofibers and stimulated with low-, medium-, or high-powered ultrasound. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays were performed on fibroblasts to measure the metabolic activity of the cells following stimulation. MTT assays showed that ultrasound-stimulated fibroblasts on PVDF-TrFE scaffolds had increased metabolic activity as power was increased, whereas on plain polystyrene, an opposite trend was observed where cells had a decreased metabolic activity with ascending levels of ultrasound power. Ultrasound-stimulated PVDF-TrFE nanofibers hold exciting potential as a therapy for PNS injuries by promoting increased metabolic activity and proliferation. The ability to noninvasively stimulate implantable piezoelectric nanofibers to promote mechanical and electrical stimulation for nerve repair offers a promising benefit to severe trauma patients.

Preclinical Evidence for the Role of Botulinum Neurotoxin A (BoNT/A) in the Treatment of Peripheral Nerve Injury

Traumatic peripheral nerve injuries tend to be more common in younger, working age populations and can lead to long-lasting disability. Peripheral nerves have an impressive capacity to regenerate; however, successful recovery after injury depends on a number of factors including the mechanism and severity of the trauma, the distance from injury to the reinnervation target, connective tissue sheath integrity, and delay between injury and treatment. Even though modern surgical procedures have greatly improved the success rate, many peripheral nerve injuries still culminate in persistent neuropathic pain and incomplete functional recovery. Recent studies in animals suggest that botulinum neurotoxin A (BoNT/A) can accelerate nerve regeneration and improve functional recovery after injury to peripheral nerves. Possible mechanisms of BoNT/A action include activation or proliferation of support cells (Schwann cells, mast cells, and macrophages), increased angiogenesis, and improvement of blood flow to regenerating nerves.