Rabbit Model for in vivo Study of Intervertebral Disc Degeneration and Regeneration

Abstract

Objective: The purpose of this study is to verify the usefulness of the rabbit model for disc degeneration study.

Materials: The L1-L2, L2-L3, L3-L4, or L4-L5 lumbar intervertebral disc (IVD) of 9 mature male New Zealand White rabbits were injured by inserting a 16-gauge needle to a depth of 5 mm in the left anterolateral annulus fibrosus while leaving L5-L6 IVD uninjured. Three other rabbits also received intradiscal injections of rabbit disc cells transfected with adenovirus and bone morphogenetic protein-2 (ad-BMP-2) at L4-L5 in addition to injury by 16-gauge needle at the L1-L2 level. Using digitized radiographs, measurements of IVD height were made and analyzed by using the disc height index (DHI). Magnetic resonance imaging (MRI) scans of the injured discs, injected discs, and uninjured L5-L6 discs were performed at 15 weeks post surgery and compared with preoperative MRI scans.

Results: All twelve rabbits showed consistent results of disc degeneration within 15 weeks following annular puncture. DHIs of injured discs were significantly lower than that of the uninjured L5-L6 discs (p<0.05). The mean value of disc degeneration grade of injured discs was significantly higher than that of uninjured discs (p<0.05). The injection of disc cell transfected with ad-BMP-2 did not induce disc regeneration at 15 weeks after injection.

Conclusion: This study showed that the injured disc had a significant change in DHI on simple lateral radiograph and disc degeneration grade on MRI scans within 15 weeks in all rabbits. Rabbit annular puncture model can be useful as a disc degeneration model in vivo.

Keywords: Animal model; Disc degeneration; Intervertebral disc; Rabbit; in vivo.

Fig. 1

Photographs of rabbit during left retroperitoneal approach. The arrow indicates an intervertebral disc of the rabbit (A). Rabbit lumbar intervertebral discs were punctured by a 16-gauge needle to a depth of 5 mm (arrow) in the left anterolateral annulus fibrosus (B).

Fig. 2

Magnetic resonance image (MRI) of rabbit at injured and uninjured discs. MRI examination was performed on all spinal columns from L1 to L6. T2-weighted MRI of the nucleus pulposus at the injured L3-L4 disc shows lower signal intensity at 15 weeks post-operation than both uninjured L5-L6 disc (B) and pre-operative L3-L4 disc (A) in the same rabbit.

Fig. 3

Lateral radiographs of a rabbit lumbar spine after annular puncture by a 16-gauge needle. Annulus of the L3-L4 intervertebral disc was punctured to induce disc degeneration. C Comparison of initial radiograph (A) and radiograph at 15 weeks after the initial annular puncture (B) shows a higher degree of disc space narrowing of the punctured L3-L4 disc compared to the uninjured L5-L6 disc.

Fig. 4

Changes in the intervertebral disc height index (DHI) after the annular puncture. The percent DHI was measured at each time to quantify changes in disc height.

Fig. 5

Change in disc degeneration grade 15 weeks after annular puncture. Pfirrmann's classification based on disc height and signal intensity from grade 1 to 5 was used to grade the disc degeneration grade of the rabbit discs. ^*p<0.05. DD : disc degeneration.

Fig. 6

A histologic section (H & E staining) of healthy, intact rabbit lumbar disc (A) and discs 15 weeks after injury (B) by 16-gauge needle (original magnification X10). Disc space narrowing and endochondral ossification of osteophyte (arrow) was apparent in the disc 15 weeks after injury.