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Friday, March 17, 2000

Cervical spine study shows differences in kinematics

The first study to document the in vivo motions of the cervical spine determined that there is a significant difference in the in vivo kinematics of the normal cervical spine, compared to a degenerative or fused cervical spine

Cervical disc degeneration can be debilitating, significantly reducing a patient's range of motion and their ability to perform normal neck motions, said presenters of scientific exhibit 69. Cervical arthrodesis, by definition, decreases neck motion and disc degeneration adjacent to fused levels is well recognized clinically. Previous kinematic studies on the human spine have been conducted under in vivo conditions, but recently fluoroscopy has been used on other joints to determine in vivo kinematics. This study focuses on the determination of the in vivo kinematics during active flexion and extension of normal, degenerated, and fused cervical spines.

Fifteen adult subjects (five with normal cervical spines; five; degenerative; and five, two-level fused) were analyzed under fluoroscopic surveillance. The subjects having a fused spine were fused at the C5-C6 and C6-C7 levels (deemed clinically successful). Fluoroscopic images were downloaded directly to a workstation computer and were analyzed at 10 various increments of spinal flexion/extension.

During the computer analysis, constant points on each of the seven cervical spine vertebrae were tracked throughout the range of motion. The points were analyzed to determine the rotation angle of each individual vertebra. The rotation of each vertebra relative to the subsequent vertebra was plotted with respect to time and the data was curve-fit to obtain a temporal function that represented the motion pattern. Using a mathematical model, the relative velocities were obtained and used to determine the partial angular and linear velocities. Kinematic comparisons were made for each subject within each group and with subjects from the other two groups.

The kinematic patterns for the three groups varied considerably. Normal cervical spines showed a smooth, arc-like motion, whereas, the degenerative spines demonstrated inconsistent motion patterns especially at the C5, C6, and C7 vertebrae (location of the degeneration). The two-level fusion patients demonstrated no motion at the fused C5-C6 and C6-C7 levels and marked abnormalities in the motion pattern at the C4-C5 level (level above fusion). There was also a distinct difference in the relative angular velocities for the three groups. The subjects having a fused spine experienced a significant change in the relative angular velocities above the fused joint.

The abrupt change in motion detected above the fused levels may lead to further complications, possibly including accelerated disc degeneration due to the abnormal loading conditions adjacent to the fused cervical segments.

The researchers from Rocky Mountain Musculoskeletal Research Laboratory, Denver, Colo., are A. Alexander M. Jones, MD, orthopaedic spine surgeon and Richard D. Komistek, PhD, president, executive director; and James T. Brumley II, MS, Colorado School of Mines.

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Last modified 23/February/2000 by IS