Spinal fusion is a common treatment for an unstable spine. But increased motion at the level above is often a problem. This is called adjacent segment degeneration. Doctors at the Oregon Health & Science University are testing a way to prevent segmental motion. Instead of ending the fusion at L5, they fused L5 to the sacrum.
Seven human cadavers (spines preserved after death for study) were used in this study. Researchers fused the L4 and S1 segments with rods and screws. They did the fusion so that each spine could be tested for a L4 and L5 fusion, as well as a L4 to S1 fusion.
Then spinal motion was measured in flexion, extension, side bending, and rotation (twisting side to side). The results of spinal segmental motion were compared for each level of fusion.
The authors report that more motion occurs in the L4 and L5 fusion. The motions affected most were flexion and extension. No changes were seen with side bending or rotation. Fusing the spine all the way down to the sacrum (S1) may protect the level at the top of the fusion (L3).