Morphological basis of radial nerve dysfunction in newborns differs from that of no radial nerve dysfunction in adults in C5–C6–C7 injuries to the brachial plexus: a cadaveric study

Abstract

Objective

Injuries to the upper and middle trunks of brachial plexus result in dysfunction of radial nerves in newborns but do not in adults. We hypothesized that the radial nerve had a lower proportion of myelinated nerve fibers (MNFs) from the lower trunk in newborns than in adults, and in newborns those MNFs were less developed than MNFs in the radial nerve from the middle and upper trunks.

Methods

We dissected bilateral brachial plexus of six newborn and six adult cadavers. The radial nerve and its fascicles were separated proximally to posterior divisions of the upper, middle and lower trunks, and fascicles of the radial nerve were harvested from three trunks to calculate respective percentage of MNFs accounting for the total number of MNFs in the radial nerve. We determined diameters of axons and g-ratios of MNFs in the radial nerve from three trunks.

Results

Compared with adults, the percentage of MNFs in the radial nerve from the lower trunk was lower (p < 0.05), from the middle trunk higher (p < 0.05) and from the upper trunk similar (p > 0.05) in newborns, though MNF counts from three trunks were higher in newborns, respectively (p < 0.01, all). In newborns, MNFs in the radial nerve from the lower trunk had smaller axonal diameters and higher g-ratios than those from the middle and upper trunks (p < 0.017, all), while in adults there were no such differences.

Conclusions

Lower proportion of MNFs in the radial nerve from the lower trunk in newborns than in adults, and in newborns immaturity of MNFs from the lower trunk relative to MNFs from the middle and upper trunks may be the major morphological basis of difference in clinical appearances of radial nerve palsy caused by injuries to C5–C6–C7 between newborns and adults.

Keywords:

• Brachial plexus injuries
• radial nerve
• spinal nerve origin
• axon and myelin development
• newborns
• adults

Ethical approval

All adult cadavers used for this study were acquired from Department of Anatomy at Shanghai Medical College of Fudan University, with informed consents signed by the donors during their lifetimes for using their bodies for scientific research and medical teaching. All newborn cadavers in this study were donated by parents for scientific research and informed consents were signed by all of them. As all cadavers in this study were deidentified and written informed consents available, we were told by the ethics committee at our institute that an approval process was not needed.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the Program of the Shanghai Municipal Key Clinical Specialty (shslczdzk05061).