INTRODUCTION

Intervertebral disc (IVD) degeneration, a common condition that often results in debilitating symptoms and functional disability, has a highly varied and complex pathophysiology. The most prevalent IVD degeneration model created by needle puncturing while effective, is unable to simulate disc degeneration process which result due to increased mechanical stress. In this study, we introduce a novel rat disc degeneration model generated by spinal destabilization surgery (SDS).

METHODS

Seven deep-frozen male rat lumbar spines were thawed and subjected to a physiological bending moment of 12.8 Nmm to test for L3/4 segmental instability. These spines were then surgically destabilized at L3/4 with L1-3 and L4-6 spinous process fixation, L3/4 supraspinous and interspinous ligaments resection, and retested for L3/4 segmental instability. During the test, the degree of flexion and the extent of posterior displacement of L3/4 were assessed.

Fifty-eight male Sprague Dawley rat (450-500g) were divided into 2 groups – sham surgery and destabilization surgery, used for in vivo study (sham 6 weeks, n = 10; destabilization 6 weeks, n = 13; sham 12 weeks, n = 15; destabilization 12 weeks, n = 20). Rats were euthanized 6 and 12 weeks after surgery for X-ray examination to calculate disc height index (DHI). The L3/4 disc-endplate segments was harvested for histopathological evaluation under FAST staining to calculate disc scores. The area and thickness of nucleus pulposus (NP) were also measured.

RESULTS

Following L3/4 destabilization, the degree of spinal flexion increased at this level (destabilization 9.79°±2.65° vs sham 6.08°±2.95°, p < 0.001). Correspondingly, posterior interlaminar displacement at this level also increased (destabilization 0.73±0.16 mm vs sham 0.35±0.18 mm, p < 0.001).

The histological examination of L3/4 disc in the destabilization groups demonstrated increased matrix in NP compartment associated with little NP cell mass, rounded lamellae cells and annular fissures. Disc scores revealed greater degeneration in the destabilization groups at both 6 weeks (destabilization 4.00±1.92 vs sham 1.10±1.91, p = 0.002) and 12 weeks (destabilization 6.60±1.35 vs sham 1.80±1.32, p < 0.001) compared to sham groups respectively. These findings corroborated with greater reduction of DHI  observed at L3/4 level in destabilization group compared to sham group at 12 weeks (destabilization 0.14±0.01 vs sham 0.12±0.01, p < 0.001), as well as reduction in NP area and thickness in destabilization group at 12 weeks by 12.3% (destabilization1.23±0.30 vs sham 1.41±0.11, p < 0.05) and 8.1% (destabilization 0.97±0.15 vs sham 1.06±0.06, p < 0.05), respectively.

DISCUSSION

This study has successfully established a novel rat IVD degeneration model by spinal destabilization surgery, substantiated by findings of reduced DHI, disc scores and decreased NP area and thickness. It provides an alternative to existing IVD degeneration models and is most suitable for application in conditions with accelerated IVD degeneration secondary to spinal instability.