Abstract
Summary Statement
To test regenerative therapies for the intervertebral disc it is necessary to create a cavity in the nucleus polposus mantaining the annulus fibrosus intact. The transpedicular mechanical nucleotomy represents the best method for this purpose.
Introduction
New cells/hydrogel based treatments for intervertebral disc (IVD) regeneration need to be tested on animal models before clinical translation. Ovine IVD represents a good model but doesn't allow the injection of a significant volume into intact IVD.
The objective of the study was to compare different methods to create a cavity into ovine nucleus pulposus (NP) by enzymatic digestion (E), mechanical discectomy (M) and a combination of both (E+M), as a model to study IVD regeneration strategies with intact anulus fibrosus (AF).
Methods
Ovine lumbar functional spinal units (FSU) were used. The transpedicular approach via the endplate route (2mm tunnel) was performed to access the NP with AF intact. FSUs were treated through M (Arthroscopic shaver), E (Trypsin/Collagenase) and E+M. The cavity was macro- and micro-scopically evaluated. The degradation of GAG (gel chromatography) around the cavity (inner AF) was assessed. The cavity volume was quantified through µCT after injection of Agarose gel/Contrast agent.
Results
The cavity has been successfully created using all methods. The M group showed high reproducibility, low GAG degradation and no endplate thinning compared to other groups. The histology analysis demonstrated NP matrix degradation in E groups while the proteoglycan content was still homogenous in the M. The percentage of the cavity volume normalised to the total IVD volume was 5.2% ± 1.6 in E, 5% ±1.4 in E+M and 4, 2% ± 0.1in M.
Discussion
M represents the best method to create a reproducible and less destructive cavity in the NP. Indeed, E-based methods perform better in terms of cavity volume but the GAG of the surrounding tissue may be affected. While a lesion of the end-plate might lead to further IVD degeneration, this approach is minimal invasive (2mm) and can be easily sealed using bone cylinder, cements or scaffolds. The biomechanical characterization and in vivo evaluation are on going.
