Artificial Disc Versus Fusion: Effect on Three-Dimensional Dynamic In Vivo Cervical Spine Motion

Intervertebral disc degeneration in the cervical spine is a common condition that often manifests as cervical disc disease, resulting in pain, motor weakness and sensory deficits. The most common surgical treatment strategy involves removal of the diseased disc and fusion of the adjacent vertebrae. Although fusion typically relieves symptoms at the surgical site, evidence of degeneration in the adjacent disc has been reported in 25–92% of patients [1,2]. It has been hypothesized that the progression of adjacent segment degeneration is a result of increased motion at the segments adjacent to the site of fusion [3]. As a response to this proposed mechanism of degeneration, artificial discs were designed with the goals of preserving motion at the operative site and maintaining normal motion in the adjacent segments. However, the extent to which normal adjacent segment motion is maintained in artificial disc patients compared to fusion patients remains unknown. Thus, the objective of this study was to compare the dynamic, three-dimensional (3D) motion of the cervical spine in fusion patients and artificial disc replacement patients.