Biomechanical comparison of anterior, posterior, and circumferential fixation after one-level anterior cervical corpectomy in the human cadaveric spine.

STUDY DESIGN

In vitro biomechanical study of cadaveric cervical spine.

OBJECTIVE

To compare the rigidity of the cervical spine after anterior, posterior, and circumferential fixation after 1-level corpectomy, and evaluate the effects of the integrity of the facet capsules and posterior ligaments (PL).

SUMMARY OF BACKGROUND DATA

Anterior cervical corpectomy is commonly used for decompression of the spinal canal in the treatment of different pathologic conditions. The effect of the integrity of the facet capsules and PLs on the biomechanical stability provided by anterior, posterior, or circumferential fixation following 1-level corpectomy has not been investigated.

METHODS

Nine cadaveric cervical spines were potted rostrally at C2, and caudally at T1-T2, and were tested in 6 directions with pure moment application, in 5 conditions: In the intact spine, after a C5 corpectomy and anterior fixation, after anterior fixation and disruption of the C4-C5 and C5-C6 facet capsules and PL, after circumferential fixation, and after posterior fixation alone without anterior cage. Angular motion of C4 relative to C6 was measured.

RESULTS

Despite C5 corpectomy, anterior grafting and plate fixation was more rigid than the intact spine with all loads in flexion, at loads of 0.5 Nm and 1.0 Nm in right axial rotation and right lateral bending, and at all loads in left lateral bending. Posterior ligamentous disruption increased motion in the coronal and axial planes, but not in the sagittal plane. Circumferential instrumentation resulted in a significant reduction in motion of the spine compared with anterior instrumentation in both the coronal and axial planes but not in the sagittal plane. Posterior fixation without anterior cage failed to limit cervical spine motion in the sagittal plane, but was restrictive in axial rotation and lateral bending when compared with circumferential fixation.

CONCLUSION

After C5 corpectomy, with intact PLs and facet capsules, anterior instrumentation is sufficient for spinal stabilization as the resultant construct is more rigid than the intact state. In the presence of C5 corpectomy with PL and bilateral facet capsule disruption, anterior plus posterior instrumentation is more rigid than anterior instrumentation alone in the axial and coronal planes and more rigid than posterior instrumentation without anterior cage in the sagittal plane.