INTRODUCTION: Exposure to vibration has been linked to a higher reporting of low back pain, and in particular disc herniation, via epidemiological studies. However, these studies are unable to determine causal relationships. In vitro tissue experimentation assists in determining if certain exposures, for example vibration, actually lead to herniation. The objectives of this study were two‐fold. First, this study aimed to determine the effect of exposure to axial vibration on the initiation and progression of disc herniation. Second, this study aimed to determine the effect of both vibration and disc damage on the mechanical properties of individual lamella from the annulus.
METHODS: Twenty functional spine units (FSU) were subjected to repetitive flexion‐extension (6000 cycles), which has been shown to produce intervertebral disc herniation. While being exposed to the repeated bending profile, ten of these FSUs were statically compressed under 1400N (control group) and the remaining ten were cyclically compressed (1260N‐1540N) at a frequency of 5 Hz (vibration group). Post collection, the intervertebral discs were further dissected and individual lamella of the annulus were tested under uniaxial tension to failure in order to assess the mechanical properties.
RESULTS: Of the ten control FSUs, four had evidence of herniation initiation while eight of the ten vibrated FSUs showed herniation initiation (chi‐square p = 0.01). No differences in disc height loss or FSU stiffness were observed between the control and vibrated groups. Further, no differences in mechanical properties were observed between the vibrated and control single lamella.
CONCLUSION: This study has confirmed that vibration is a causal mechanical risk factor that significantly increases the occurrence of herniation. Interestingly, vibration in conjunction with repeated flexion‐extension does not seem to alter the acute failure mechanical properties of lamella when compared to lamellae only exposed to flexion‐extension, suggesting that herniation is a complex injury.