Abstract

The surgical standard of care for lumbar discectomy leaves the annulus fibrosus (AF) defect unrepaired, despite considerable risk for a recurrent herniation. Identification of a viable defect repair strategy has until now been elusive. The scope of this ex vivo biomechanical study was to evaluate crosslinking hydrogels as potentially promising AF defect sealants, and provide a baseline for their use in combination with collagen scaffolds that restore disc volume. This study directly compared genipin crosslinked fibrin hydrogel (FibGen) as a promising preclinical candidate against a clinically available adhesive composed of glutaraldehyde and albumin (BioGlue). Forty-two bovine coccygeal functional spine units (FSU) were randomly allocated into four groups, namely untreated (control, n = 12), repaired with either one of the tested hydrogels (BioGlue, n = 12; FibGen, n = 12), or FibGen used in combination with a collagen hydrogel scaffold (FibGen+Scaffold, n = 6). All specimens underwent a moderate mechanical testing protocol in intact, injured and repaired states. After completion of the moderate testing protocol, the samples underwent a ramp-to-failure test. Lumbar discectomy destabilized the FSU as quantified by increased torsional range of motion (28.0° (19.1, 45.1) vs. 41.39° (27.3, 84.9), p<0.001), torsional neutral zone (3.1° (1.2, 7.7) vs. 4.8° (2.1, 12.1), Z = -3.49, p < 0.001), hysteresis(24.4 J (12.8, 76.0) vs. 27.6 J (16.4, 54.4), Z = -2.61, p = 0.009), with loss of both disc height (7.0 mm (5.0, 10.5) vs 6.1 mm (4.0, 9.3), Z = -5.16, p < 0.001) and torsional stiffness (0.76 Nmdeg-1 (0.38, 1.07) vs. 0.66 Nmdeg-1 (0.38, 0.97), Z = -3.98, p < 0.001). Most FibGen repaired AF endured the entire testing procedure whereas only a minority of BioGlue repaired AF and all FibGen+Scaffold repaired AF failed (6/10 vs. 3/12 vs. 0/6 respectively, p = 0.041). Both BioGlue and FibGen+Scaffold repaired AF partially restored disc height (0.47 mm (0.07, 2.41), p = 0.048 and 1.52 mm (0.41, 2.57), p = 0.021 respectively) compared to sham treatment (0.08 mm (-0.63, 0.88)) whereas FibGen-only repaired AF had no such effect (0.04 mm (-0.73, 1.13), U = 48.0, p = 1). The AF injury model demonstrated considerable change of FSU mechanics that could be partially restored by use of an AF sealant. While inclusion of a volumetric collagen scaffold led to repair failure, use of FibGen alone demonstrated clinically relevant promise for prevention of mechanical reherniation, outperforming an FDA approved sealant in this ex vivo test series.

Highlights

  • Intervertebral disc herniation is one of the most frequent causes of low back pain [1,2,3]

  • We evaluated the most promising of these hydrogels to be used in combination with a collagen scaffold to account for loss of disc height (3).Collagen scaffolds may enable a favorable environment for secondary tissue ingrowth and repair

  • Post-hoc pairwise comparisons of the significant outcome variables disc height and compressive stiffness revealed a significant difference in disc height gain of BioGlue (0.47 mm (0.07, 2.41), U = 18.0, p = 0.048) and FibGen + Scaffold (1.52 mm (0.41, 2.57), U = 3.0, p = 0.021) but not FibGen (0.04 mm (-0.73, 1.13), U = 48.0, p = 1) repaired annulus fibrosus (AF) compared to the control group (0.08 mm (-0.63, 0.88)) after Bonferroni-correction

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Summary

Introduction

Intervertebral disc herniation is one of the most frequent causes of low back pain [1,2,3]. Lumbar discectomy has emerged as the most commonly applied and effective method for surgical treatment of intervertebral disc herniation [4,5]. Current practice involves removal of herniated material through the AF defect or through a surgical incision, leaving an unrepaired defect within the AF. Discectomy is associated with loss of disc height, torsional stiffness and NP fluid pressurization [8]. These changes of intervertebral disc (IVD) biomechanics yield decreased joint stability and have been linked to accelerated IVD and facet joint degeneration [8,9,10]. No reliably effective method for AF repair has been established

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