Introduction: Modic changes (MCs), signal variations in the vertebral trabeculae adjacent to the endplate, have long been suspected as a pathological cause of back pain. A number of theories have been proposed to explain the occurrence of MCs, including mechanical stress alteration, low-virulent infection, and autoimmune inflammation, yet to date a validated and universally accepted animal model of MCs has not been established. This study is aimed to examine whether cartilaginous endplate (CEP) destruction can lead to endplate and vertebral marrow signal changes (Modic changes) on magnetic resonance (MR) image.
Methods: Sixteen rabbits were used in the study, and the L2-6 intervertebral discs were exposed using an anterolateral approach. The L4/5, L3/4 and L2/3 discs underwent annulotomy, annulotomy and CEP curettage, annulotomy and chemoneuclelysis, respectively. Magnetic resonance (MR) imaging was performed preoperatively, and 1, 3, and 6 months postoperatively to evaluate the presence or absence of MCs and signal intensity changes of subchondral vertebral marrow. After the last imaging, animals were sacrificed for histological study, with specific focuses on endplate pathologies and their association with MCs.
Results: Among discs underwent CEP curettage or chemoneuclelysis, there were 6 (9.4%), 19 (29.7%), and 32 (50%) endplates presented MCs at 1, 3 and 6 months, respectively. Signal intensity of the subchondral vertebral marrow was significantly higher in CEP curettage and chemonucleolysis groups than in annulotomy alone group at 1, 3, 6-month (p<0.05 for all) MR follow-up. Histological study revealed that both surgical curettage and chemopapain injection successfully induced CEP destruction. In the presence of full layer CEP defects, more endplates presented MCs on MR images (59.6% vs 11.4%, p<0.001). Moreover, endplates with MCs had greater histological degeneration score than those without (8.97±1.92 vs 5.35±2.28, p<0.001) and higher expression levels of inflammatory factors (IL-1β, TNF-α, and IL-6, p<0.05 for all) in the subchondral vertebrae.
Discussion: CEP destruction, induced either by physical curettage or chemical lysis, can lead to Modic-like signal changes on MR images. CEP degeneration was closely associated with the presence of MCs, suggesting that the loss of CEP integrity may be the root pathology underlying MCs on MR images.
Key words: Modic changes, cartilaginous endplate, chemoneucleolysis, magnetic resonance, inflammation.