Mapping Subchondral Bone Density Distribution in the Canine C6-C7 Vertebral Endplates: A CT-OAM Study

SIMPLE SUMMARY: Treating cervical spinal cord compression in dogs can be complex, especially when dynamic instability is involved, a concern not fully addressed by standard surgery. A common approach includes using intervertebral cages to support and stabilize the affected area. However, the risk of cage subsidence into the vertebral endplates can undermine treatment effectiveness. In this study, we used computed tomography osteoabsorptiometry to map the subchondral bone density in the C6-C7 vertebral motion unit of dogs. This density serves as an indicator of endplate mechanical stability. Similar to humans, we found that bone density within the endplate is unevenly distributed. The central and centro-dorsal regions have low bone density, making them less stable. This correlates with the common site of cage subsidence. Our findings suggest a need to reconsider the design and placement of spinal cages. Positioning them on areas of higher bone density, such as the ventral, dorsal, and lateral extensions of the vertebral endplates, may reduce the risk of subsidence, improving treatment outcomes. ABSTRACT: Intervertebral cage subsidence is a common complication in treating disc-associated cervical spondylomyelopathy in dogs. The mechanical stability of the vertebral endplate in contact with the cage is crucial to preventing subsidence. This study aims to assess subchondral bone mineral density (sBMD) in the canine vertebral endplate (specifically, the C6-C7 vertebral motion unit) as a measure of its mechanical stability. The sBMD distribution was mapped for the C6 caudal and C7 cranial vertebral endplates in 15 middle- to large-breed dogs using computed tomography osteoabsorptiometry. The sBMD distribution in the canine C6 and C7 vertebral endplates exhibited a heterogeneous pattern, with lower density observed in the central and dorsal contact areas of the nucleus pulposus, where common subsidence occurs. Our results suggest a potential need to redesign intervertebral cages to ensure that contact areas align with regions of higher bone density. A broad-based design extending toward the lateral and dorsal aspects of the annulus fibrosus contact area may enhance stability.