The evolution of stability in cervical spinal constructs using either autogenous bone graft or methylmethacrylate cement. A follow-up report on a canine in vivo model.

Thirty-six adult mongrel dogs underwent either a posterior C4-C5 bone graft or methylmethacrylate-cerclage wire construction procedure to simulate the analogous human stabilization procedures. The dogs were divided into groups of six and allowed to live 1, 2, or 3 months after surgery. At the appropriate time they were killed and their C4-C5 spinal segments excised and studied radiologically, mechanically, and histologically. In addition, the C4-C5 spinal segments from 15 other mongrel dogs were excised and either left intact as normal (five) or prepared as one of the two constructs (five each) described above. They were also tested mechanically to provide immediate postoperative stability data. At some time during the first postoperative month the methylmethacrylate constructs lost mechanical stability. In addition, fibrous tissue was noted to have grown between the posterior laminal surface and the cement mass during this same time. Radiologically, loosening was obvious by the second postoperative month. The bone graft constructs were mechanically equivalent to or superior to the normal dogs by the second postoperative month. Likewise, they were well on their way to solid fusion radiologically and histologically by the same time. Impressed by the rapidity of deterioration in mechanical stability for the methylmethacrylate constructs, the authors further questioned their usefulness in cases of traumatic cervical spinal instability. The bone graft constructs continued to appear to be a reliable way to achieve ultimate spinal stability.