Introduction: Discectomy of herniated intervertebral discs (IVDs) successfully alleviates associated neurological symptoms but fails to repair the underlying degenerative disc process. Persistent annular defect post discectomy is associated with increased risk of reherniation, progressive IVD degeneration, and chronic low back pain. Recently, we demonstrated the ability of riboflavin crosslinked high-density collagen gels (HDC) to facilitate annular repair in vivo [1]. In this study, AF fibrochondrocytes were seeded in the HDC gel to enhance the reparative process at the site of annular defect.

Methods: 24 athymic rats, punctured with an 18-gauge needle in the tail disc, were divided into three groups: 1) untreated (n=4); 2) injected with crossliked HDC (n=10); 3) injected with fibrochondrocyte-laden crosslinked HDC (n=10). Sheep AF fibrochondrocytes labeled with DiI at a concentration of 106 cells/ml were mixed with HDC gels prior to injection. MR imaging and histological sections were performed.

Results: Compared to the puncture, untreated group, at 1 week, both HDC gel groups showed significantly higher retention of NP size and hydration, while only the cell-laden group better maintained NP retention up to 5 weeks based on repeated measure ANOVA. The untreated discs showed substantial NP herniation by 2 weeks and NP absence with signs of degeneration by 5 weeks (Fig 1a, b). Implanted fibrochondrocytes were detected by DiI in the process of reorganization of the gels (Fig 2a). Histological assessments indicate that while gels influence the sealing of the defect, the addition of cells accelerates the reparative process at the site of the annular defect as early as 2 weeks (Fig 2b).

Conclusions: We are the first to demonstrate that AF fibrochondrocyte-laden HDC gels have the ability to better repair annular defects than acellular gels, thereby suggesting their potential feasibility in cell-based therapy for annular defects.

Patient Care: The cellular collagen gels can provide an injectable treatment inducing biological repair for annular defect, which is a pathological culprit in disc hernia and underlying process in disc degeneration.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of developing a novel treatment for annular defect, 2) Discuss, in small groups, therapeutic strategies using cells and scaffolds 3) Identify an effective treatment for lumbar disc hernia and subsequent degenerative disc diseases.

References: 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 (Phila Pa 1976). 2014 Feb 1;39(3):198-206.