Abstract
Intervertebral disc degeneration is one of the leading causes of back pain, but treatment options remain limited. Recently, there have been advances in the development of biomaterials for nucleus augmentation; however, the testing of such materials preclinically has proved challenging. The aim of this study was to develop methods for fabricating and testing bone-disc-bone specimens in vitro for examining the performance of nucleus augmentation procedures. Control, nucleotomy and treated intervertebral disc specimens were fabricated and tested under static load. The nucleus was removed from nucleotomy specimens using a trans-endplate approach with a bone plug used to restore bony integrity. Specimen-specific finite element models were developed to elucidate the reasons for the variations observed between control specimens. Although the computational models predicted a statistically significant difference between the healthy and nucleotomy groups, the differences found experimentally were not significantly different. This is likely due to variations in the material properties, hydration and level of annular collapse. The deformation of the bone was also found to be non-negligible. The study provides a framework for the development of testing protocols for nucleus augmentation materials and highlights the need to control disc hydration and the length of bone retained to reduce inter-specimen variability.
Highlights
Four out of five adults will suffer low back pain during their lifetime, with many going on to suffer further acute episodes, imposing a high economic and social burden on society.[1,2,3] Low back pain is strongly associated with degeneration of the intervertebral discs, which causes a loss of hydration of the tissue and reduces its swelling pressure
One challenge is to represent the biomechanical behaviour of the degenerated disc in vitro without compromising the integrity of the annulus fibrosis, so that the only damage to the annulus is caused by the simulated nucleus augmentation procedure itself
The data associated with this article are openly available from the University of Leeds Data Repository.[28]
Summary
Four out of five adults will suffer low back pain during their lifetime, with many going on to suffer further acute episodes, imposing a high economic and social burden on society.[1,2,3] Low back pain is strongly associated with degeneration of the intervertebral discs, which causes a loss of hydration of the tissue and reduces its swelling pressure. One challenge is to represent the biomechanical behaviour of the degenerated disc in vitro without compromising the integrity of the annulus fibrosis, so that the only damage to the annulus is caused by the simulated nucleus augmentation procedure itself. Previous studies have simulated degeneration by enzymatic digestion[7,8,9] or by physical removal of the nucleus tissue using a trans-endplate nucleotomy.[5,10,11,12,13] The former requires a lengthy incubation period and is difficult to standardise, while the latter requires drilling through the Measuring jig axially clamps specimen (1) between locating jaws (2). Cutting jig axially clamps specimen (4) via adjustable supports (5) and base clamp (6). A hacksaw blade is introduced between the jig body and removable guide plate (7), which ensures cuts are perpendicular to the longitudinal tail axis
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