Intervertebral Disc Dynamics and Degeneration

Degenerative disc disease is a serious health problem worldwide, whose etiological basis – mechanical stimulus, biochemical changes, or natural aging – is poorly understood. While the disc’s known function is that of dynamic shock absorber, its dynamic response has not been fully characterized throughout the disc health spectrum (from healthy to degenerate). Therefore, this study aimed to correlate the radiographic ‘clinical’ appearance of disc degeneration with its in vitro dynamic response. Post mortem macaque tissues were utilized in a correlation study of the lumbar spine. Fifty-four functional spinal units (T10-11, T12-L1, and L6-7) from eighteen animals were excited with cyclic loading (5 to 80-Hz) and a dynamic impulse. From these, the natural frequency, stiffness, and energy absorption of each disc was correlated with its level of degeneration. No differences in mechanical properties were found between the spinal levels blocking by degeneration grade. The natural frequency of the intervertebral disc increased with degeneration grade from 51 Hz to 70 Hz. Intervertebral disc stiffness exhibited an increase between the healthy and severely degenerated tissues while the energy absorption decreased over the health spectrum. Degeneration was found to significantly affect disc dynamics which may aid in identifying the etiology of this disease.