Staged Phrenic Nerve Elongation and Free Functional Gracilis Muscle Transplantation-A Possible Option for Late Reconstruction in Chronic Brachial Plexus Injury

PURPOSE

In patients with late brachial plexus birth injuries, sequelae after acute flaccid myelitis, or chronic adult brachial plexus injury, donor nerves for functioning muscle transplantation are often scarce. We present the results of a potential strategy using the phrenic nerve with staged free gracilis transplantation for upper extremity reanimation in these scenarios.

METHODS

A retrospective review was performed on an institutional database of brachial plexus injury or patients with palsy. All patients underwent a staged reconstruction in which the ipsilateral phrenic nerve was extended by an autogenous nerve graft (PhNG), followed by free-functioning gracilis transplantation (PhNG-gracilis).

RESULTS

Nine patients (6 cases of late brachial plexus birth injuries, 2 of acute flaccid myelitis, and 1 of adult chronic brachial plexus injury) were included in this study. The median follow-up period following the PhNG-gracilis procedure was 27 months (range, 12-72 months). The goals of the staged PhNG and PhNG-gracilis were primarily finger extension or finger flexion. In some patients, the technique was used to improve both elbow and finger function, tunneling the muscle through the flexor compartment of the upper arm and under the mobile wad at the elbow. All patients exhibited improvement of muscle strength, including in finger extension (4 patients) from M0 to M2; finger flexion (3 patients) from M0 to M3; elbow extension (1 patient) from M0 to M2; and elbow flexion (1 patient) from M2 to M4.

CONCLUSIONS

A 2-stage PhNG-gracilis may restore or enhance the residual elbow and/or finger paralysis in chronic brachial plexus injuries. A minimum follow-up period of 3 years is recommended. This technique may remain useful as one of the last reconstructive options to increase power in patients with scarce donor nerves.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic V.

The role of stretching in slow axonal transport

Axonal stretching is linked to rapid rates of axonal elongation. Yet the impact of stretching on elongation and slow axonal transport is unclear. Here, we develop a mathematical model of slow axonal transport that incorporates the rate of axonal elongation, protein half-life, protein density, adhesion strength, and axonal viscosity to quantify the effects of axonal stretching. We find that under conditions where the axon (or nerve) is free of a substrate and lengthens at rapid rates (>4 mm day⁻¹), stretching can account for almost 50% of total anterograde axonal transport. These results suggest that it is possible to accelerate elongation and transport simultaneously by increasing either the axon's susceptibility to stretching or the forces that induce stretching. To our knowledge, this work is the first to incorporate the effects of stretching in a model of slow axonal transport. It has relevance to our understanding of neurite outgrowth during development and peripheral nerve regeneration after trauma, and hence to the development of treatments for spinal cord injury.