Background: To histologically evaluate lumbar involvement in rheumatoid arthritis (RA) by investigating rats with collagen-induced arthritis (CIA) and to assess the potential effects of RA on the discovertebral joints and facet joints.
Methods: Seven-month-old female Sprague-Dawley rats were divided into groups with CIA and without CIA (control). All rats were sacrificed at 8 weeks after initial sensitization and the lumbar spine (L5/6) was harvested. Then the lumbar spine block specimens were stained with Villaneuva bone stain and sectioned in the midsagittal plane. The left facet joints were also sectioned in the midaxial plane. Specimens were studied under a microscope and infiltration of inflammatory cells was investigated.
Results: In the CIA group, lumbar lesions were observed in 13/18 rats (76%). Lymphocytes infiltrated into the anterior rim of the vertebral bodies only in 2 rats, while lymphocytes infiltrated the facet joints only in 4 rats. Both sites were involved in 7 rats. In addition, osteoclasts invaded the anterior rim of the vertebral bodies and formed cavities that also contained lymphocytes. Formation of pannus was seen in the facet joints in 11/18 rats.
Conclusion: In CIA rats, infiltration of inflammatory cells into the anterior rim of the vertebral bodies alone or into the facet joints alone was demonstrated in 2 rats and 4 rats, respectively, while both sites were involved in 7 rats. Therefore, lesions at the anterior rim of the vertebral body did not arise secondary to facet joint involvement, but were caused by CIA along with synovial lesions of the facet joints.
Keywords: collagen-induced arthritis rat; lumbar spine; rheumatoid arthritis.