Geometric and morphological changes of the intervertebral disc under fatigue testing

OBJECTIVE: To understand the injury mechanism of the intervertebral disc at different loading rates and to explore the anatomic and histological changes of intervertebral discs. DESIGN: Fresh porcine lumbar spines were used for fatigue testing to study the morphological changes of the intervertebral disc. BACKGROUND: Intervertebral disc problem is one of the most common causes that lead to low back pain. Slow repetitive loading was considered to be the critical factor of spine and disc injuries. METHODS: Twenty-four lumbar functional units were subjected to cyclic loading at three different loading rates. The geometric measurements and magnetic resonance image observations were conducted for the comprehension of morphological changes. The detail observation was taken through a stereomicroscope. RESULTS: There was no significance in geometric changes between different loading rates. For magnetic resonance imagings, morphological changes included the changes of nucleus pulposus shape, bulge of anterior and posterior longitudinal ligaments, and dehydration in annulus fibrosus. CONCLUSION: The morphological changes of intervertebral disc were revealed in certain kinds of lesions. The results imply that fatigue failure and degeneration or instability are strongly linked. The correlation of magnetic resonance imaging and anatomic observation showed a high correspondence in the comparison of shape and position of the nucleus pulpasus. RELEVANCE: The changes of geometric measurements and relationship between anatomic observation and magnetic resonance imaging finding had been analyzed. It could help in understanding the mechanism of triggering cause in the early stage of disc degeneration.