Pathomechanics of Early-Stage Lumbar Intervertebral Disc Degradation Leading to Discogenic Pain-A Narrative Review

Abstract

Although the existence of highly prevalent pain, disability, and work time lost associated with discogenic low back pain is well known, the recognition of the culpability of universally present disc degradation and mechanical insufficiency in the first three decades of life is often overlooked. There is a corresponding "treatment gap" and no current interventions with demonstrated capabilities to address the pain and resist the usual progression of increasing structural failure of spinal tissues with increasing levels of pain and disability. This narrative review summarizes more than forty years of the literature describing the pathomechanics of progressive degradation of lumbar discs, with a focus on studies that implicate an increasing mechanical insufficiency in the etiology of early-stage chronic and recurrent discogenic low back pain. Topics highlighted in this review include the deleterious biological changes that begin soon after birth, stress intensification due to the loss of fluid phase load support, fatigue weakening and damage accumulation in non-regenerative tissue, disc tears, segmental instability, and the timeline for first incidence of chronic low back pain. The review concludes with preferred treatment characteristics and a brief summary of emerging treatment approaches.

Keywords: biomechanics; degradation; discogenic low back pain; lumbar intervertebral disc; pathoetiology.

Figure 1

Factors contributing to the vicious cycle of disc structural degradation and mechanical insufficiency during the first 3 decades of life: loss of cell viability [15,18]; loss of fluid phase load support [19,20,21]; fatigue weakening of tissues [1,21,22]; accumulated microdamage [16,22]; and disc tears [23,24,25,26,27,28].

Figure 2

Schematic depiction of loss of lumbar intervertebral joint motion constraint resulting from progressive mechanical degradation of disc tissues. Non-degraded joint motion is depicted by the blue curve; degraded joint motion is depicted by the red curve. Increased neutral zone reflects a loss of passive tissue constraint and increased instability in the region of the motion curve that has the least resistance.