A biomechanical analysis of C2 corpectomy constructs.

BACKGROUND CONTEXT: Reconstruction of C2 after tumor destruction and resection remains a significant challenge. Most constructs use a strut graft with plate or screw fixation. A novel C2 prosthesis (cage/plate construct) combining a titanium mesh cage with bilateral C1 shelves and a T-plate has been used successfully in 18 patients. Supplemental posterior instrumentation includes C0-C3 or C1-C3 fixation. Biomechanical comparisons of this C2 prosthesis with traditional fixation options have not been reported.

PURPOSE: To investigate and compare the stability of the novel cage/plate construct with a conventional strut graft and plate construct.

STUDY

DESIGN

An in vitro, cadaveric biomechanical study of C2 replacement constructs.

METHODS

Seven fresh-frozen cadaveric human spines (C0-C5) were tested intact. Next, the cage/plate and strut graft/plate constructs were tested with occiput-C3 and C1-C3 posterior instrumentation. Pure moment loads (up to 1.5 Nm) were applied in flexion/extension, lateral bending, and axial rotation. Motion was evaluated using a three-camera motion analysis system. Statistical significance was evaluated using one-way repeated measures analysis of variance with Student-Newman-Keuls post hoc pairwise comparisons.

RESULTS

All constructs provided a statistically significant decrease in motion in this C2 corpectomy model as compared with the intact condition. There was no statistical difference in C1-C3 motion between the four constructs in lateral bending, regardless of whether the occiput was included in the posterior fixation. Other significant differences were detected in flexion-extension and axial rotation, and these differences were dependent upon the type of anterior reconstruction and whether the occiput was included in the posterior fixation.

CONCLUSIONS

Under acute loading conditions, both the cage/plate and strut graft/plate constructs provided initial stability beyond that of the intact specimen. For some reconstructions the occiput does not need to be included in the posterior instrumentation in order to obtain equivalent stability across the C1-C3 spinal space.