Remodeling of vertebral bone after outer anular injury in sheep

Study Design. This study uses semiautomated histoquantitative techniques to analyze subchondral bone architecture in adult merino sheep up to 2 years after outer anular cuts were created in lumbar discs. Objectives. To describe morphometric changes to the adjacent vertebral bone structure in the lumbar spine, and to discuss these in relation to the pathology of other spinal components. Summary of Background Data. Disc degeneration has been observed in the sheep lumbar spine 4-6 months after surgery to the outer anulus, whereas biomechanical testing has shown earlier changes. Methods. Lumbar discs with adjacent subchondral trabecular bone were sectioned using standard histologic methods. An image-analyzing computer was used to measure morphometric indices of bone structure. Results. Trabecular bone volume was elevated significantly by 2 months because of consolidation of existing trabeculae and formation of new elements. The changes were evident 2 years after surgery. Conclusion. Subchondral trabecular bone appears to be sensitive to changes in the disc after outer anular injury. There is evidence that these structural changes are influenced by changes in the biomechanical behavior of the incised disc.