An Injectable Hyaluronic Acid Hydrogel Promotes Intervertebral Disc Repair in a Rabbit Model

Study Design: An in vivo model to study the effect of an injectable hyaluronic acid (HA) hydrogel following puncture-induced lumbar disc injury in rabbits.

Objectives: The aim of this study was to determine the efficacy of an injectable HA hydrogel to maintain disc height and tissue hydration, promote structural repair, and attenuate inflammation and innervation in the lumbar discs.

Summary Of Background Data: Previously, we have demonstrated that HA hydrogel alleviated inflammation, innervation, and pain to promote disc repair. Nevertheless, the effect of an injectable HA hydrogel in the lumbar disc in a weight-bearing animal model was not performed.

Methods: We have adopted a surgically puncture-induced disc injury at lumbar levels in a rabbit model. The discs were grouped into sham, puncture with water injection, and puncture with HA hydrogel injection. Postoperatively, we measured changes in disc height using x-ray. We used magnetic resonance imaging to assess disc degeneration on tissue hydration after euthanasia. Post-mortem, we determined histological changes, innervation (PGP9.5) and inflammation (interleukin [IL]-6, IL-1β, and tumor necrosis factor [TNF]-α) in the discs.

Results: We have demonstrated a significant reduction of disc height and T2/T1ρ mapping with histological evidence of degenerative discs, increase of innervation and inflammation in puncture-induced disc injury over time. In the HA hydrogel group, disc height was increased at weeks four and eight. A slight increase of T2 mapping, but significantly in T1ρ mapping, was observed in the HA hydrogel group at week 8. We observed homogenous NP distribution and organised AF lamellae at week eight and a slight reduced innervation score in the treatment group. HA hydrogel significantly downregulated IL-6 expression at day 1. This, however, was only slightly reduced for IL-1β and TNF-α.

Conclusion: An injectable HA hydrogel had the protective effects in suppressing the loss of disc height, promoting tissue hydration for structural repair, and attenuating inflammation and innervation to prevent further disc degeneration.Level of Evidence: N/A.