INTRODUCTION: Nucleus augmentation using hydrogel provides immediate weightbearing and a means for biological treatment. This study evaluated effects of a hyaluronic acid‐based hydrogel (HAgel) plus/minus supplementation with TGF‐β3 (TGFβ3) growth factor on repair of anulus‐punctured rabbit intervertebral discs (IVD) using plain radiography, micro CT (μCT), and MRI.
METHODS: Two discs (L2/3, L4/5) in 24 New Zealand White rabbits were punctured. At week‐4 post‐puncture, saline, HAgel (MW˜1 MDa, ˜80% water, ˜30 kPa shear modulus), or HAgel+TGFβ3 (10 ng/ml) were injected (20 μl) into punctured discs of the animals (n=8), and sacrificed at week 16. Disc Height Index (DHI), % ratio of IVD to vertebral body height, was determined on radiographs every 2 weeks. T2 values of the nucleus and anulus were deter‐mined using 3T MRI spin echo sequence. Threedimensional (3D) Disc Height was determined on μCT data as the minimum distance between opposing endplates. All measures were normalized to L3/4 values.
RESULTS: DHI decreased to ˜75% by week‐4 (rmANOVA p<0.05) and then increased with time for both treatment groups (p<0.05 vs. saline). In the NP, T2 values (Fig.A) were the highest in the HAgel group, but treatment effect was not significant (p=0.3). In the AF (Fig.B), HAgel group had significantly higher (p<0.01) T2 values than saline group. 3D disc height (Fig.C) was also higher in the HAgel group (p<0.05 vs. saline). T2 values of the NP correlated with 3D disc height (Pearson R2=0.45, p<0.001). (cont'd)
DISCUSSION: These results suggest sensitivity of the imaging measures to our model of disc repair using HAgel. HAgel treatment restored DHI, T2 values and 3D disc height compared to the saline control, suggesting treatment efficacy. Mechanical support and hydrophilic nature of HAgel may have increased disc height and T2 values. Work remains to understand degradation characteristic of HAgel in vivo, and its long‐term effectiveness.