Phrenic nerve transfer to the musculocutaneous nerve for the repair of brachial plexus injury: electrophysiological characteristics

VATS phrenic nerve harvesting for brachial plexus neurotization: literature review and our experience

INTRODUCTION

Brachial plexus traumatic lesions often lead to severe upper extremity deficits that dramatically compromise quality of life of mostly young patients. Optimal treatment aims to restore elbow flexion transferring various donor nerves. Phrenic nerve (PN) is a powerful source of transferable axons and, despite supraclavicular sectioning being the most used technique, it can be harvested through video-assisted thoracoscopic surgery (VATS).

EVIDENCE ACQUISITION

About PN harvesting, less than 20 articles were found in Literature. Most of them are clinical case-reports or case-series or expert opinions. Most of these studies are from China and East Asia and very rarely from Europe; none from Italy. Therefore, we present our experience in PN VATS harvesting in two patients, first cases reported in Italy.

EVIDENCE SYNTHESIS

Few papers explore risks and benefits of PN as a donor site for brachial plexus reconstruction. There is no clear consensus in the literature whether a traditional approach or minimally invasive surgery is advisable to harvest PN for neurotization. Currently there's no clear indication nor a definitive contraindication about routine use of PN for surgical treatment of BPTLs, it's mostly a matter of choosing the best donor nerve for every single patient. This choice depends on the patient's characteristics, type of traumatic lesion, time from the traumatic event and on the center's experience. The only real concern about using PN as a donor is the potential loss of pulmonary function. In our center two patients with complete brachial plexus avulsion underwent PN transfer via VATS in 2021. Usually, recovery of muscle function depends on time between injury and surgical repair. A commonly accepted recommendation is to perform surgery within six months from the traumatic lesion12. In our experience, the time between trauma and surgery was five months for patient A and six months for patient B. Even if some authors13 consider previous thoracic trauma with rib fractures a major contraindication for homolateral PN harvesting, we believe that the presence of pleural adhesions should not exclude a patient from surgery. No intra or postoperative complications were observed. Both patients were discharged on IV postoperative day. An intense rehabilitation program within three months after surgery is mandatory and regular follow-up is needed to monitor any improvement. No respiratory symptoms or discomfort is recorded up to now.

CONCLUSIONS

Nerve transfer is a safe and reliable surgical reconstructive procedure and phrenic nerve, due to its pure motor nature, is a very good donor for brachial plexus injuries14. VATS is a valid procedure to guarantee a much longer nerve, avoiding any graft use, and doesn't seem to determine significant pulmonary function loss. Previous thoracic trauma, rib fractures and pneumothorax are commonly considered contraindications for VATS harvesting. However, a major trauma leading to BPTL often implies homolateral thoracic trauma with or without rib fracture or pneumothorax. This could be a reasonable justification to reconsider those contraindications and extend the potential cohort of patients that could benefit from this technique.

Proteomic analysis of trans-hemispheric motor cortex reorganization following contralateral C7 nerve transfer

Nerve transfer is the most common treatment for total brachial plexus avulsion injury. After nerve transfer, the movement of the injured limb may be activated by certain movements of the healthy limb at the early stage of recovery, i.e., trans-hemispheric reorganization. Previous studies have focused on functional magnetic resonance imaging and changes in brain-derived neurotrophic factor and growth associated protein 43, but there have been no proteomics studies. In this study, we designed a rat model of total brachial plexus avulsion injury involving contralateral C₇ nerve transfer. Isobaric tags for relative and absolute quantitation and western blot assay were then used to screen differentially expressed proteins in bilateral motor cortices. We found that most differentially expressed proteins in both cortices of upper limb were associated with nervous system development and function (including neuron differentiation and development, axonogenesis, and guidance), microtubule and cytoskeleton organization, synapse plasticity, and transmission of nerve impulses. Two key differentially expressed proteins, neurofilament light (NFL) and Thy-1, were identified. In contralateral cortex, the NFL level was upregulated 2 weeks after transfer and downregulated at 1 and 5 months. The Thy-1 level was upregulated from 1 to 5 months. In the affected cortex, the NFL level increased gradually from 1 to 5 months. Western blot results of key differentially expressed proteins were consistent with the proteomic findings. These results indicate that NFL and Thy-1 play an important role in trans-hemispheric organization following total brachial plexus root avulsion and contralateral C₇ nerve transfer.

Study of synergistic role of allogenic skin-derived precursor differentiated Schwann cells and heregulin-1β in nerve regeneration with an acellular nerve allograft

Development of tissue structure and three-dimensional microenvironment is crucial for regeneration of axons in the peripheral nerve repair. In this study we aimed to evaluate the efficacy of nerve regeneration by using an acellular nerve allograft (ANA) injected with allogenic skin-derived precursor differentiated Schwann cells (SKP-SCs) and heregulin-1β. Skin-derived precursor cells (SKPs) were generated from dermis of newborn (postnatal day 2) Wistar rats. In a rat model, nerve regeneration was determined across a 15 mm lesion in the sciatic nerve by using an ANA injected with allogenic SKP-SCs and heregulin-1β. The electrophysiological analysis, histological examination and electron microscopy were involved in this study. Cultured SKPs expressed nestin and fibronectin, and differentiated into cells with phenotype of SCs that presented characteristic markers of p75NGFR and S100-β. Implantation of SKP-SCs into the rat models by using ANA and allogenic skin-derived precursor differentiated Schwann cells (SKP-SCs) increases sciatic nerve functional index (SFI), peak amplitudes, nerve conduction velocities, number of myelinated fibers within the graft, while reduces incubation period, sciatic nerve injury-induced weight and contractions loss. Using ANA injected with SKP-SCs combined with heregulin-1β greatly promote peripheral nerve repair in a rat model. Our results suggest that SKP-SCs transplantation with heregulin-1β represents a powerful therapeutic approach, and facilitates the efficacy of acellular nerve allograft in peripheral nerve injury, though the detailed mechanism remains to be elucidated.