Morphological cervical disc analysis applied to traumatic and degenerative lesions

Trauma and degenerative pathologies at the lower cervical spine are different from lumbar spine pathologies. However, the description of cervical discs is classically taught similarly to that of the lumbar discs. Recent studies have raised this issue, and in 1999, Mercer and Bogduk described ventral annulus fibrosus as a crescent-shaped interosseous ligament. We propose a metric analysis of the different components of the cervical disc to examine this description. We analyzed 140 sagittal and coronal transections of 35 discs. These discs were taken from seven cervical spines at the five lower levels, C2-C3, C3-C4, C4-C5, C5-C6 and C6-C7. We measured quantitative parameters on sagittal, para-sagittal, ventral coronal and dorsal coronal colored transections: disc length (L), ventral annulus thickness (VAF), lateral annulus thickness (LAF), dorsal annulus thickness (DAF), length of the fibrocartilaginous tissue (FC), sagittal and coronal fibrocartilaginous core ratio (% Core) and intra-disc cleft length (Cleft). We also measured two qualitative parameters: degenerative disease of cartilaginous end plates and total intra-disc cleft. Finally, we examined 114 transections, and 18.5% were ruled out. The results showed thick ventral annulus fibrosus, thin lateral annulus and a very thin dorsal annulus. Fibrocartilaginous tissue filled the dorsal sagittal half of the disc. Intra-disc cleft split the fibrocartilaginous tissue and spread through the ventral annulus only six times. The shape of the ventral annulus at the lower cervical spine is compared to a pivot-hinge device. The aspect is functionally discussed in regard to teardrop fractures, unilateral locked facet syndrome and degenerative changes in the unco-vertebral area.