Biomechanical Analysis of an Anterior Cervical Discectomy and Fusion Pseudarthrosis Model Revised With Machined Interfacet Allograft Spacers.

Abstract

Biomechanics study. To evaluate the biomechanical advantage of interfacet allograft spacers in an unstable single-level and 2-level anterior cervical discectomy and fusion (ACDF) pseudoarthrosis model. Nine single-level and 8 two-level ACDF constructs were tested. Range of motion in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) at 1.5 N m were collected in 4 testing configurations: (1) intact spine, (2) ACDF with interbody graft and plate/screw, (3) ACDF with interbody graft and plate/loosened screws (loose condition), and (4) ACDF with interbody graft and plate/loosened screws supplemented with interfacet allograft spacers (rescue condition). All fixation configurations resulted in statistically significant decreases in range of motion in all bending planes compared with the intact spine (<i>P</i> < .05). <i>One Level.</i> Performing ACDF with interbody graft and plate on the intact spine reduced FE, LB, and AR 60.0%, 64.9%, and 72.9%, respectively. Loosening the ACDF screws decreased these reductions to 40.9%, 44.6%, and 52.1%. The addition of interfacet allograft spacers to the loose condition increased these reductions to 74.0%, 84.1%, and 82.1%. <i>Two Level</i>. Performing ACDF with interbody graft and plate on the intact spine reduced FE, LB, and AR 72.0%, 71.1%, and 71.2%, respectively. Loosening the ACDF screws decreased these reductions to 55.4%, 55.3%, and 51.3%. The addition of interfacet allograft spacers to the loose condition significantly increased these reductions to 82.6%, 91.2%, and 89.3% (<i>P</i> < .05). Supplementation of a loose ACDF construct (pseudarthrosis model) with interfacet allograft spacers significantly increases stability and has potential applications in treating cervical pseudarthrosis.