Annular Repair Using Cross-Linked High Density Collagen Gel Seeded with Fibrochondrocytes: In Vivo Outcomes of a Rodent Disc Study
Authors: Pennicooke Brenton , Moriguchi Yu , Borde Brandon , Berlin Connor , Grunert Peter , Bonassar Lawrence , Härtl Roger 
Published: April 2016

Introduction

Despite alleviating associated neurological symptoms, discectomy of herniated intervertebral discs (IVDs) fails to repair the underlying degenerative process. Persistent annular defect post discectomy is associated with increased risk of reherniation, progressive IVD degeneration, and chronic low back pain.1–7 Although many studies have previously employed cell transplantation to regenerate the nucleus pulposus (NP), few have focused on annulus fibrosus (AF) repair. Recently, we demonstrated the ability of riboflavin crosslinked high-density collagen gels (HDC) to facilitate annular repair in vivo.8,9 In this study, we assessed the in vivo efficacy of AF fibrochondrocytes seeded in a gel scaffold at enhancing the the repair of an annular defect to prevent further degenerative changes in a post-puncture rat-tail model.

Material and Methods

38 athymic rats, punctured with an 18-gauge needle in the tail disc, were divided into 3 groups: untreated ( n = 6), injected with crosslinked HDC ( n = 16), and injected with fibrochondrocyte-laden crosslinked HDC ( n = 16). At 1, 2, and 5 weeks postoperatively, a series of in vivo images with X-ray and 7T MRI were conducted to determine the disc height index and nucleus pulposus (NP) size and hydration, respectively.8,10,11 Histological assessments were performed to evaluate the viability of implanted cells, degree of annular repair and secondary disc degeneration. The study was approved by and undertaken in accordance with guidelines outlined by the Hospital for Special Surgery Institutional Animal Care and Use Committee and New York State. For the analyses of continuous outcomes in disc height index, NP size, and NP hydration, we employed linear regression models with a generalized estimating equation and robust standard errors to estimate differences in mean changes from baseline controls (discectomy) across displaced and stable implantation groups. P values < 0.05 were considered statistically significant.

Results

The untreated discs showed substantial NP herniation at two weeks and NP absence with signs of degeneration by five weeks, resulting in 40% loss of disc height. Both HDC gel groups, cellular and acellular, had significant retention of disc height and NP voxel count over the course of five weeks. Average NP voxel counts of cellular gels were higher than those of acellular gels at all time points and statistical significance was achieved at 1 week. Only the cellular group restored NP hydration relative to that of the adjacent healthy control. Further histological assessments indicate that while HDC gels influence the sealing of the defect, the addition of cells generates abundant tissue growth and extracellular matrices at the site of the annular defect, accelerating the reparative process. Disruption of endplate was observed in the puncture group, but not in the treated segments.

Conclusion

In vivo studies on the cell-based annular repair are few in number. Our preliminary findings suggest that fibrochondrocytes can potentially improve HDC gel-based annular repair. A long term study with sufficient sample size are necessary to confirm these results. References Bruske-Hohlfeld I, Merritt JL, Onofrio BM, et al. Incidence of lumbar disc surgery. A population-based study in Olmsted County, Minnesota, 1950-1979. Spine 1990;15(1):31–35 Carragee EJ, Han MY, Suen PW, Kim D. Clinical outcomes after lumbar discectomy for sciatica: the effects of fragment type and anular competence. J Bone Joint Surg Am 2003;85-A(1):102–108 Laus M, Bertoni F, Bacchini P, Alfonso C, Giunti A. Recurrent lumbar disc herniation: what recurs? (A morphological study of recurrent disc herniation). Chir Organi Mov 1993;78(3):147–154 Barth M, Weiss C, Thomé C. Two-year outcome after lumbar microdiscectomy versus microscopic sequestrectomy: part 1: evaluation of clinical outcome. Spine 2008;33(3):265–272 O'Connell GD, Malhotra NR, Vresilovic EJ, Elliott DM. The effect of nucleotomy and the dependence of degeneration of human intervertebral disc strain in axial compression. Spine 2011;36(21):1765–1771 Frei H, Oxland TR, Rathonyi GC, Nolte LP. The effect of nucleotomy on lumbar spine mechanics in compression and shear loading. Spine 2001;26(19):2080–2089 DePalma MJ, Ketchum JM, Saullo TR, Laplante BL. Is the history of a surgical discectomy related to the source of chronic low back pain? Pain Physician 2012;15(1):E53–E58 Grunert P, Borde BH, Hudson KD, Macielak MR, Bonassar LJ, Härtl R. Annular repair using high-density collagen gel: a rat-tail in vivo model. Spine 2014;39(3):198–206 Borde B, Grunert P, Härtl R, Bonassar LJ. Injectable, high-density collagen gels for annulus fibrosus repair: An in vitro rat tail model. J Biomed Mater Res A 2015;103(8):2571–2581 Grunert P, Hudson KD, Macielak MR, et al. Assessment of intervertebral disc degeneration based on quantitative magnetic resonance imaging analysis: an in vivo study. Spine 2014;39(6):E369–E378 Grunert P, Borde BH, Towne SB, et al. Riboflavin crosslinked high-density collagen gel for the repair of annular defects in intervertebral discs: An in vivo study. Acta Biomater 2015;26:215–224