Study Links Cervical Segment Changes to Fused Bone Grafts

Biomechanical changes in adjacent segments after a C4-7 fusion may be inversely proportional to the number of bone grafts used in the procedure, according to recent study results.

The study investigated the motion patterns, disc stresses, and facet loads at the segments adjacent to a C4-7 fusion when the number of bone grafts used for the reconstruction is varied.

“Increasing the number of bone grafts for reconstruction was associated with a decrease in the range of motion at the instrumented level and a corresponding increase at the adjacent segments,” Mozammil Hussain, Ph.D., and colleagues wrote. Hussain is an assistant professor at Logan University in Chesterfield, Mo.

The researchers found stresses in adjacent-segment discs were greatest in the one-graft model they studied, followed by the two-graft model. Stresses were least in the three-graft model, according to the findings. Also, facet loads were the greatest in the one-graft model, followed by the two-graft model, and they were least in the three-graft model, based on the results.

Hussain and colleagues used a computed tomography scan of a healthy 38-year-old woman, as well as a 3-D finite element model of an intact C3-T1 segment to study these changes. They built three C4-7 fusion models from the intact model, varying the number of bone grafts used.

The one-graft model of a two-level corpectomy procedure was developed using a single long-strut bone graft between the C-4 inferior and the C-7 superior endplates. The two-graft model of a combined corpectomy-discectomy was created by placing one bone graft between the C-4 inferior and the C-6 superior endplates and used another bone graft at the C6–7 following discectomy. The three-graft model—a three-level discectomy procedure—was constructed via disc replacement at C4-5, C5-6 and C6-7 and performed with three bone grafts.

The investigators ultimately assessed range of motion, disc stresses, and posterior facet loads at the segments superior (C3-4) and inferior (C7-T1) to the fusion to draw their conclusions.