The Evolution of Stability in Cervical Spinal Constructs Using Either Autogenous Bone Graft or Methylmethacrylate Cement

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Abstract
Adult mongrel dogs (36) underwent either a posterior C4-C5 [cervical] bone graft or methylmethacrylate-cerciage wire construction procedure to simulate the analogous human stabilization procedures. The dogs were divided into groups of 6 and allowed to live 1, 2, or 3 mo. 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 (5) or prepared as 1 of the 2 constructs (5 each) described. They were also tested mechanically to provide immediate postoperative stability data. At some time during the 1st postoperative mo. 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 2nd postoperative mo. The bone graft constructs were mechanically equivalent to or superior to the normal dogs by the 2nd postoperative mo. 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, their usefulness in cases of traumatic cervical spinal instability was studied. The bone graft constructs continued to appear to be a reliable way to achieve ultimate spinal stability.