Cervical discs are not smaller versions of those found in the lumbar regions. The anterior, posterolateral and posterior annulus fibrosis (AF) as well as the nucleus pulposus (NP) will be considered below.
The annulus fibrosis of the L/S discs envelop the nucleus pulposus completely with 15-25 concentric rings, which alternate in angulation around 70 (Pooni, Hukins et al. 1986; Urban and Roberts 2003). Movement at the L/S disc are flexion/extension and lateral flexion – these movements are tilting movements and are accommodated by bulging of the disc (Penning 1988). Rotation is limited because rotation is resisted by the annulus in the L/S even when posterior elements are removed (Penning 1988; Dolan and Adams 2001). The lumbar disc suffers herniations and tears, which can be painful (Urban and Roberts 2003).
The NP of the L/S is a fluid, gelatinous core of the disc with hydrostatic properties and takes up 50% of the entire disc (Mercer SR and Jull 1996; Sato, Kikuchi et al. 1999; Edmondston, Song et al. 2000; Dolan and Adams 2001; Mercer S 2003; Urban and Roberts 2003).
Compared to the lumbar discs, the cervical discs differ in the annulus in a number of ways. Firstly, there are not concentric lamellae around a fluid NP. The anterior annulus is more like a crescent-shaped mass of fibres that taper towards the posterolateral corners of the disc (Mercer S and Bogduk 1999; Bogduk and Mercer 2000; Mercer S 2003). The orientation of these fibres are more of an interweaving rather than separate layers of lamellae that alternate in direction like that found in the L/S (Mercer S and Bogduk 1999) and they converge superiorly to the lower anterior edge of the vertebral body above(Mercer S 2003). The lateral corners of the cervical disc, in the uncovertebral regions, there is no substantive annulus at all, just a thin layer of fascial tissue (Mercer SR and Jull 1996; Mercer S and Bogduk 1999; Bogduk and Mercer 2000; Mercer S 2003; Urban and Roberts 2003). Posteriorly there are thin, vertically orientated fibres, not the multi-layered, alternating orientation seen in the L/S (Mercer SR and Jull 1996; Mercer S and Bogduk 1999; Dolan and Adams 2001; Mercer S 2003; Urban and Roberts 2003).
Lastly, the NP in the adult cervical disc has been described more as a fibrocartilaginous core as opposed to a fluid, gelatinous core as seen in the L/S (Mercer S and Bogduk 1999; Mercer S 2003). Also, clefts form in the uncovertebral region across the posterior disc, which seems to aid and protect the disc from degeneration and assist rotation (Penning 1988; Mercer S and Bogduk 1999; Bogduk and Mercer 2000; Mercer S 2003). The disc also becomes split into cranial and caudal sections (Penning 1988; Mercer S 2003). This is a normal development in the cervical disc of adults and coincides with the development and maturation of the uncinate processes (Mercer SR and Jull 1996; Mercer S 2003). The NP also has higher levels of collagen, which are thought to be reflective of the stresses incurred in the C/S (Mercer SR and Jull 1996). Developmentally, the NP in the cervical disc at birth is only about 25% of the total disc (Mercer S and Bogduk 1999).
In summary, there are large morphological, biochemical and functional differences between cervical and lumbar discs as listed above.