Corpectomy versus discectomy for the treatment of multilevel cervical spine pathology: a finite element model analysis

Background contextAfter multilevel fusions, construct failure because of pseudoarthrosis and instrumentation complications is a well-recognized clinical problem. Little is known about the biomechanics governing the cervical spine after different anterior reconstruction techniques, specifically the number of bone grafts and screws used and whether discectomies versus corpectomies have been performed. A few research groups have compared the efficacy of corpectomy and discectomy procedures under common testing conditions; however, no quantitative stress measurements at graft–end plate and bone-screw interfaces have been reported to date.PurposeTo test the hypothesis that increasing the number of bone grafts and screws would yield a more stable construct and decrease the stresses at the graft–end plate and bone-screw interfaces.Study designStability of fusion constructs with three different multilevel reconstruction techniques.MethodsA previously validated C3–T1 intact finite element model was modified to evaluate three different anterior C4–C7 fusion models: a two-level corpectomy alone (one graft and four screws), a corpectomy-discectomy (two grafts and six screws), and a three-level discectomy alone (three grafts and eight screws). Two unicortical screws were placed parallel to the corresponding end plates inside the vertebral bodies—C4 and C7 for the corpectomy alone; C4, C6, and C7 for the corpectomy-discectomy; and C4, C5, C6, and C7 for the discectomy alone. Range of motion, graft stresses, end plate stresses, and bone-screw stresses were evaluated.ResultsAlthough total construct motion decreased with an increasing number of bone grafts and screws, this was not significantly different between reconstruction techniques. Stresses in the bone grafts, end plates, and bone near screws decreased as a result of increasing the number of bone grafts and screws, thereby confirming the present study hypothesis.ConclusionsAlthough the chances of pseudarthrosis have been shown to be lower after multilevel cervical corpectomy versus discectomy, because of fewer bone-graft interfaces required for healing, this benefit should be weighed against the higher bone-screw stresses, operating time, blood loss, and costs associated with corpectomy. Future biomechanical studies focusing on corpectomy and discectomy procedures in similar testing protocols are warranted to compare the findings presented here.