We investigated the effects of cervical disc herniation on kinematics of adjacent segmental motion by evaluating 407 patients using kinetic MRI. For each patient, measurements for translational motion (mm), angular variation (degrees) and disc height (mm) were obtained at each segment from C2/C3 through C7/T1. The results show that the spinal levels above the disc herniation experienced, on average, a 7.2% decrease in translational motion per millimeter of disc herniation (p=0.0113), but no significant change in angular motion. Spinal levels below the herniation experienced a 5.2% decrease in angular motion per millimeter of disc herniation (p=0.0236) without significant change in translational motion. Disc herniation had no significant impact on disc height at adjacent levels, although disc degeneration at the level of herniation correlated with decreased disc height above and increased disc height below. This study indicates that although disc height, translational motion and angular variation are significantly affected at the level of a disc herniation, no significant changes are apparent within the adjacent segments. Herniated discs have no effect on the range of motion at adjacent levels regardless of the degree of disc degeneration or the size of disc herniation. The natural progression of disc herniation and adjacent segment disease within the cervical spine appear to be separate, unrelated processes.
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