Biomechanical Factors Affecting The Disc

Introduction

There is no longer any doubt that lumbar intervertebral discs can directly cause low back pain. Anatomical studies have identified nociceptive nerve endings within the outer annulus fibrosus (Bogduk 1994), and pain-provocation studies on sedated patients have demonstrated that their symptoms of severe back pain can be reproduced by direct mechanical stimulation of the posterior annulus fibrosus (Kuslich et al. 1991). The purpose of the present paper is to suggest how mechanical loading might cause lumbar discs to become painful in some people. The first section, which describes experiments on cadaveric spines, shows how mechanical loading can lead to disc injury (including prolapse) or fatigue failure, and how sustained loading in certain postures can lead to high concentrations of compressive stress within the annulus. Later sections describe experiments on living people which indicate the everyday circumstances which could lead to disc injury and/or pain.

Key Words::

• intervertebral discs
• lumbar vertebrae
• weight lifting