COLLAGENS IN THE INJURED PORCINE INTERVERTEBRAL DISC

Spinal pain often is thought to be due to degeneration and mechanical failure of the intervertebral disc. Since the mechanical strength of t he tissue depends on collagen fibers, the present study was designed t o investigate the reactions in collagen metabolism after an experiment ally induced disc injury. Five domestic pigs underwent an incision in the anterior part of the annulus fibrosus of disc L4-L5 through a retr operitoneal approach. The animals were killed 3 months postoperatively , and the injured discs and intact discs (controls) from different ani mals were removed for chemical analysis. Slices were cut from seven di fferent parts across the disc. The concentration of total collagen (hy droxyproline [Hyp]), the activities of the two key enzymes in collagen biosynthesis (prolyl 4-hydroxylase [PH] and galactosylhydroxylysyl gl ucosyltransferase [GGT]), and the concentration of mature collagen cro sslinks (hydroxypyridinium [HP]) were determined. In all experimental discs, the morphology had changed considerably: the nucleus pulposus w as small, fibrous, and yellowish. The annular lamellar structure was p artially destroyed and had been replaced by granulation tissue in the region of the injury. Large osteophytes had formed at the ventral edge s of the vertebral bodies. In the nucleus pulposus, the Hyp concentrat ion and the activities of PH and GGT were significantly increased, whe reas the water content had decreased. The concentration of HP crosslin ks was decreased in the anterior annulus fibrosus.