Correlation between electromyography findings and plasticity grading score after long-term phrenic nerve to musculocutaneous nerve transfer in brachial plexus injuries.

OBJECTIVE

Patients with complete traumatic brachial plexus injuries often require nerve transfers to restore lost function. Phrenic nerve (PN)-musculocutaneous nerve (MCN) transfer can be used to restore elbow flexion. The degree to which reinnervated muscles achieve independent control requires central plastic changes. The central program of the PN donor nerve needs to disconnect and establish connections with that of the recipient MCN. This study aimed to improve understanding of the brain's changes after PN-MCN transfer by correlating electromyography (EMG) findings with clinical plasticity grading scale (PGS) scores.

METHODS

A prospective study was conducted on patients who underwent PN-MCN transfer after brachial plexus injury. EMG assessments were systematically performed under 3 distinct conditions: 1) normal respiration with the arm at rest, 2) deep respiration with the arm at rest, and 3) voluntary elbow flexion performed without inspiration. Motor unit potentials (MUPs) detected within a 150-msec interval were systematically categorized using a 5-point scale. Brain plasticity was clinically evaluated using the 4-point PGS.

RESULTS

Twelve patients with a mean age of 21.8 years were included in the study. A significant negative correlation was found between EMG activity during deep breathing and PGS outcomes (correlation coefficient [CC] -0.623, p = 0.031). Likewise, EMG activity during deep breathing showed a negative correlation with EMG activity during voluntary elbow flexion (CC -0.811, p = 0.002). Only 1 patient (8%) demonstrated complete disconnection between the donor and recipient neural pathways.

CONCLUSIONS

The authors' findings indicate a significant correlation between clinical measures of brain plasticity and EMG outcomes. Additionally, complete cerebral disconnection was rarely attained, with most patients retaining residual influence from the original donor function.