Experimental traction injuries of ventral spinal nerve roots. A scanning electron microscopic study

The aims of this experimental scanning electron microscopic study were to identify the levels at which cervical ventral nerve roots, or the rootlets by which they are attached to the spinal cord, rupture under traction and to document the resulting damage. This information would provide the basis of a rationale for repairing rootlet avulsions which may follow brachial plexus traction injuries in man and which cause severe impairment of upper limb function. Traction was applied to C4 to T1 ventral roots until rupture occurred, in 10 freshly fixed and three living anaesthetized Wistar albino rats and in one human post-mortem specimen. Rupture occurred at the rootlet-cord junction in 80% of cases. Most individual myelinated fibres broke at the central-peripheral nervous system (CNS-PNS) transitional node which, in the cervical region, lies at the bottom of an endoneurial invagination surrounding each fibre and extending deep to the cord surface. Fibre rupture at more distal levels occurred internodally, and a length of axon commonly protruded well beyond the level of sheath rupture. Some sheaths broke cleanly across but the torn surfaces of others tapered, perhaps because of rupture at Schmidt-Lanterman incisures. The cellular and connective tissue rootlet sheaths ruptured where they were continuous with the pia mater. Ruptured fixed and unfixed tissues were ultrastructurally similar. It is clear from the findings of this study that regeneration would take place entirely in a PNS environment. The endoneurial invaginations would ensure that sprouts emerging from transitional nodes would be guided distally into rootlets surgically apposed to the torn transitional zone.