Normal, Fused, and Degenerative Cervical Spines: A Comparative Study of Three-Dimensional in Vivo Kinetics
Fei Liu, PhD; Joseph S. Cheng, MD, MS; Richard D. Komistek, PhD; Mohamed R. Mahfouz, PhD

Introduction

With a complex system of intervertebral discs and adjoining ligaments and muscles, the cervical spine provides support and stability to the head, transfers the weight of the head to the trunk, and allows for complex physiological motions. The technique of anterior cervical discectomy decompression and fusion has been successfully used in the treatment of the degenerative cervical spine for decades1-3. However, it has been reported that 2.9% of fused cervical spines per year will require revision surgery at adjacent levels for the treatment of progressive spondylosis and that 25.6% of patients who undergo anterior cervical discectomy decompression and fusion will have new disease at an adjacent level within the first ten years after surgical treatment4. Also, prior in vitro studies have reported greater motions and increased load and intradiscal pressures along with a higher prevalence of degeneration at the segments adjacent to the level of the initial anterior cervical discectomy decompression and fusion as compared with those in a normal cervical spine4-6. The variations in the relative motions and forces occurring at the levels adjacent to the fused levels have been thought to be responsible for the further degeneration seen in the cervical spine.

In vivo, three-dimensional kinetics of the cervical spine could provide a more direct method to evaluate the results of this surgical technique in conjunction with clinical assessment. Currently, three-dimensional in vivo loading conditions are primarily determined with use of either telemetric implants or mathematical models7-9. Given that telemetric systems are limited to the collection of kinetic data within diseased joints, the possibility of obtaining relevant kinetic information with use of telemetry in a normal, nondiseased joint for comparison would not be feasible7. Alternatively, mathematical modeling has been shown to be …


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