Microsurgical anatomy of the dorsal cervical nerve roots and the cervical dorsal root ganglion/ventral root complexes

BACKGROUND: It is known that a 'dissociated motor loss' of the deltoid muscle can occur with disconcerting frequency after cervical spine surgery. The etiology of this entity is in question. We conducted an artatomic study to identify anatomic factors that might predispose C5 to injury. METHODS: We studied 128 dorsal cervical nerves and root ganglion/ventral root complexes in 10 adult cadavers. At each cervical level the following data were recorded: number of rootlets, range of width of rootlets, length of DREZ, cranial angles of the superior and inferior rootlets with the spinal cord, length of the superior and inferior rootlets, dimensions of the foramina, dimensions of the dorsal root, dimensions of the dorsal root ganglion (DRG)/ventral root (VR) complex, and the blood supply to the DRG. The histology at the site of compression was also examined. Statistical analysis was conducted using the single factor-repeated measures analysis of variance. RESULTS: We found that, 1) the C5 superior dorsal rootlets angle less inferiorly from the cervical cord than the other dorsal cervical roots (p = 0.001), 2) the majority of the DRG/VR complexes from C3 to C6 were compressed by the vertebral artery (73%), 3) the C5 DRG/VR complex was compressed to the greatest extent (77.6%, p = 0.3519), and 4) the ganglionic artery was more frequent at C4, C5, and C6. CONCLUSION: To our knowledge, the second finding has not been reported previously. The first and third findings may help explain why C5 is more vulnerable to injury.