Experimental traction injuries of cervical spinal nerve roots: a scanning EM study of rupture patterns in fresh...

This study examines the levels at which fresh rat ventral and dorsal C4 to T1 spinal roots rupture under traction stress. Rupture rarely occurs at the CNS-PNS transitional zone. Despite its delicate appearance this is strengthened in a number of ways, so that it is less vulnerable than the roots and their constituent rootlets and aggregated rootlet bundles (ARBs). Ventral roots commonly rupture either where the rootlets join to form the ARBs, along the course of the latter, or where these in turn join to form the ventral root. Dorsal root rupture shows a similar pattern but has a higher frequency of rupture within the root proper than is the case with the ventral roots. The level of rupture also varies systematically over the series of roots examined: rupture points tend to be located at more distal levels in caudal roots. This may occur because of mechanical differences in the distribution of traction stress along roots, related to their courses through the vertebral canal. Upper roots run transversely and the traction force is transmitted directly to rootlet levels, while more caudal roots run obliquely and tend to rupture where they are drawn taut against the pedicle. Many of the morphological features of ruptured roots would tend to inhibit regeneration of fibres distally. Differences in the pattern of rupture between fresh and fixed roots are examined. The latter tend to rupture at levels closer to the CNS than the former.