Lightning Podiums: Spinal Gumbo - 803A

Presented by: S. Miyazaki

Author(s):

S. Miyazaki(1,2), K. Kato(1), K. Chang(1), W.C. Bae(3), Y. Sun(4), W. Jiang(4), J. Yamada(1), E. Abarado(1), E. Linn(1), C. Muehleman(1), M.E. Lenz(1), R.L. Sah(1), A.D. Diwan(5), K. Masuda(1)

(1) University of California, San Diego, Departments of Orthopaedic Surgery, La Jolla, CA, United States
(2) Kobe University Graduate School of Medicine
(1) Departments of Orthopaedic Surgery, Kobe, Japan
(3) University of California, San Diego, Departments of Radiology, La Jolla, CA, United States
(4) University of California, San Diego, Departments of Bioengineering, La Jolla, CA, United States
(5) St. George Hospital University, Orthopaedics Research Institute and Department of Orthopaedic Surgery, Sydney, NSW, Australia

Abstract

Introduction: A single injection of growth differentiation factor-6 (GDF6/BMP13) at the time of anular stab in sheep has shown positive effects on preserving disc structures by increasing collagen and proteoglycan accumulation [1]. To reveal clinical efficacy, the effects of a single injection of various doses of GDF6 on disc height (two-dimensional (2D) and 3D) and magnetic resonance imaging (MRI) and histological grades were determined in the rabbit anular-puncture model.

Methods: Rabbit anular-puncture disc degeneration model and the injection of GDF6: Female New Zealand white rabbits (n=32) were used in this study. Under general anesthesia, the anulus fibrosis was punctured with an 18-gauge needle (5 mm depth) in two non-contiguous discs (L2/3 and L4/5). Four weeks after the initial puncture, either vehicle (phosphate-buffered saline (PBS); 10 µL per disc) or GDF6 (1, 10 or 100 µg in PBS, 10 µL per disc) was injected into the center of the nucleus pulposus (NP) using a 26-gauge needle. Radiographic analysis of disc height: Intervertebral disc (IVD) height was obtained from lateral radiographs and expressed as disc height index (DHI). The DHI was normalized to the preoperative DHI (%DHI) and further normalized to the DHI of the L3/4 non-punctured disc. Micro computed tomography (µCT) and 3D disc height distribution (DHD): The average minimum distance between apposing bony endplates was calculated as the DHD using reconstructed 3D surfaces and further normalized to the DHD of L3/4. To determine regional repair variations, DHDs in five zones (posterior, left-lateral, anterior, right-lateral, and central regions) were computed. MRI analyses: The degeneration grade of IVDs was classified according to Pfirrman using T2 weighted images. Histological analyses: Midsagittal histologic sections (HE and Safranin O) were graded using our established protocol [2]. Statistical analyses: All data are expressed as mean and standard error (SE). Comparisons among the experimental groups were analyzed using two-way analysis of variance (ANOVA) or the Kruskal-Wallis test.

Results: DHI (Fig. A): Repeated two-way ANOVA revealed that treatment significantly affected %DHI in the GDF6 10 and 100 ug groups (P< 0.05). At week 16, three GDF6 groups showed a significant increase in %DHI. DHD (Fig. B, C): The zonal DHD of the posterior region in the GDF6 groups was significantly higher than that in the PBS group (P< 0.05). MRI degeneration grade (Fig. D, E): The Pfirrman grade was significantly lower in the GDF6 10 and 100 µg groups compared to the PBS group (P< 0.05). Histological grade: GDF6 injection did not show any significant effects compared to PBS injection.

Discussion: The injection of GDF6 into the NP at four weeks after anular puncture restored disc height, especially in the posterior zone, and improved the MRI grade. The data indicated that GDF6 injection can induce structural changes at 10-100 µg. In a separate study, GDF6 injection into discs reduced pain generation in the xenograft rat radiculopathy model. These results suggest that an injection of GDF6 changes the pathological status of degenerated discs and reduces pain generation and, therefore, may serve as a new therapeutic approach for degenerative disc disease.