The use of coccygeal discs to study intervertebral disc metabolism.

There have been very few studies on the metabolism of the intervertebral disc. One possible reason is that lumbar discs suitable for in vitro synthesis studies are difficult to obtain. We have examined some properties of coccygeal discs to see if those discs are a suitable alternative. The properties measured appear similar to those of lumbar discs, with collagen content lowest in the nucleus and highest in the outer annulus, while hydration and glycosaminoglycan content were highest in the nucleus and of a similar level to those of canine lumbar discs (approximately 83% water). The discs were under mechanical load in vivo, resulting in an equilibrium swelling pressure of 0.25-0.3 MPa. The 35S-sulphate incorporation rate was 2-5 x 10(-5) mmol/g dry weight per hour in the inner annulus and nucleus, in comparison with 2-3 x 10(-5) mmol/g dry weight per hour in rabbit and canine lumbar discs. Coccygeal discs are a readily obtainable and cheap source of disc material, and they are easy to dissect out. Since the general properties of these discs are similar to those of lumbar discs, we suggest that they are a suitable model for the study of the metabolic and other properties of lumbar discs.