Mechanisms of anular failure resulting from excessive intradiscal pressure : A microstructural-micromechanical investigation

Microstructural/micromechanical investigation of pathways of anular wall disruption. To investigate the fundamental mechanisms by which both intralamellar and interlamellar relationships are disrupted by nuclear pressurization. Understanding how anular failure might occur following increased nuclear pressurization requires an experimental approach that avoids artifactual injury to the anulus but reveals structural disruption resulting directly from the pressurization event. Bovine motion segments were subjected to internal pressurization using a novel "through vertebra" gel injection method. Intralamellar and interlamellar sections were deliberately chosen so as to expose systematic patterns of structural disruption resulting from the pressurization event. This microdisruption was investigated using a novel method that combined microtensile manipulation and simultaneous differential contrast imaging of the fully hydrated unstained sections. The inner anulus was most severely disrupted, the middle regions developed a series of regular clefts along axes of weakness within the in-plane arrays, with only mild array disruption occurring in the outer regions. A mechanism is proposed whereby an anular failure pathway, driven by hydrostatic nuclear pressure, could track through the complex anular structures via a set of disruptive events causing weakening of both the in-plane and interlamellar junction interconnections.