Effects of Cervical Fusion on Facet JointsIt is well known that after spinal fusion, increased stress is placed on the vertebral bones, joints, and discs above and below the fusion. But what happens at all the other levels of the cervical (neck) spine when just one level is fused?
Researchers at the Department of Biomedical Engineering (University of Tennessee) studied seven adult human cadavers to help answer this question. After fusing one-single but different level in each spine, motion testing was done. A total of seven spines were used to test each level of the cervical spine.
A special motion-tracking system was used to track motion for each cervical vertebra. All six motions (flexion, extension, side bending and rotation to both sides) were measured.
The authors report the motion changes observed at each cervical level for all seven fusions. They looked for trends in motion reduction. They found that when the two lowest levels of the cervical spine were fused (C56 and C67), increased flexion and extension motion were measured at the level just above and just below the fusion.
There were differences in how the facet joints were affected. Each vertebra in the cervical spine has two facet joints on each side. Each joint is made up of two parts. The superior segment of the joint (the one on top) connects to the vertebra above. The inferior segment (the one below) joins with the vertebra below.
When the lower part of the cervical spine was fused (C5 to 7), the inferior segments of the facet joint just above were affected the most. When the upper part of the cervical spine was fused (C3 to C5), greater motion occurred in the superior segments.
Movements to the right and left were not equally affected. This may be explained by differences in tissue quality. It could also be caused by the effect of being right- or left-handed. Dominance may change movement patterns unevenly.
The authors conclude increased motion in the spine after fusion does occur and may speed up spinal degeneration at other levels. This is the first study to show specific effects on each facet joint.
John S. Schwab, MSc, et al: Motion Compensation Associated with Single-Level Cervical Fusion: Where Does the Lost Motion Go? In Spine. October 1, 2006. Vol. 31. No. 21. Pp. 2439-2448.
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