Lumbar intervertebral disc herniation following experimental intradiscal pressure increase.

Abstract

An experimental biomechanical model of overload and rupture of the annulus fibrosus (AF) and lumbar disc herniation was achieved by increasing intradiscal pressure while keeping disc height constant in 69 motion segments at the L4-L5 level excised from cadaveric spines. The experiments were made on 53 specimens in neutral posture and on 16 specimens in flexion posture. The values found for the rupture intradiscal pressure (RIP) ranged from 750 to 1300 kPa for neutral posture and the maximum RIP in anterior flexion was 1177 kPa. The degree of disc degeneration was assessed by vertebral transcorporeal discography (previous to experiment) and by sectioning the intervertebral disc after the experiment. The herniated lumbar intervertebral disc model by intradiscal pressure increase makes possible these assertions: * The correlation between the degree of AF degeneration and the RIP is significant: the maximum RIP corresponds to a non-degenerated AF and the less RIP can tear only a degenerated AF; so disc herniation only occurs to discs with torn AF. * AF breaking is more often paramedian, left or right. The place of AF breaking was paramedian in 70.3% cases, median in 9.45% cases and posterolateral in 20.25% cases.