In vitro biomechanics, randomized control trial.
The objectives of this study were 2-fold: ﬁrst, to determine the effect of exposure to axial vibration on the initiation and progression of disc herniation; second, to determine the effect of vibration exposure and the presence of disc damage on the mechanical properties of individual lamella from the annulus.
Summary of Background Data.
Vibration exposure has been linked to a higher reporting of low back pain and 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.
A total of 20 porcine (aged, 6–8 months; similar skeletal development as an adolescent human) 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 ﬂexion/extension, 10 FSUs were statically compressed under 1400 N (control group) and the other 10 were cyclically compressed (1260–1540 N) at a frequency of 5 Hz (vibration group). Post collection, intervertebral discs were dissected and individual lamella of the annulus was tested under uniaxial tension to failure (tension applied perpendicular to the orientation of the collagen ﬁbers) to isolate the mechanical properties of the intralamellar matrix.
Of the 10 control FSUs, 4 had evidence of herniation initiation while 8 of the 10 vibrated FSUs showed herniation initiation (P ∇ 0.01). No signiﬁcant differences in disc height loss or FSU stiffness were observed between the control and vibrated groups. Further, no signiﬁcant differences were observed between the 2 groups for any of the single lamella mechanical properties.
This study conﬁrmed that vibration is a causal mechanical risk factor that signiﬁcantly increases the occurrence of herniation.