Introduction: Although there is evidence that neck motion is different between arthroplasty with artificial-disc (AD) and anterior cervical fusion (ACF), studies are limited to vertebral body motion.[1] The objective of this study was to compare cervical foraminal dimensions during neck extension and axial rotation between ACF and AD.

Methods: Seventeen patients who underwent C5C6 ACF and 7 who underwent C5C6 AD were enrolled in the study. Biplane x-ray images were acquired at 120Hz during three trials of axial neck rotation and extension.[2] A thin-slice CT scan was also acquired of the cervical-spine and the vertebrae were manually reconstructed into 3D bone models for use with the model-based tracking system.[2] Custom software was used to place four anatomical landmarks per foramen(Fig 1). Foraminal height and width were then calculated as the 3D distance between the supero-inferior and antero-posterior (AP) markers, respectively, for each frame of data.

Results: At the operated level(C5C6), the median and range of foraminal height were smaller in ACF than in AD during axial rotation and extension (p<0.007,p<0.02). The minimum foraminal height was also smaller in ACF during neck extension (p<0.04)(Fig. 2). At the superior adjacent level(C4C5), the range of foraminal width was greater in ACF than in AD patients during extension (p<0.05) (Fig. 3). At the nonadjacent level(C3C4), the ranges of foraminal height (p<0.02) and width (p<0.002) were also greater in ACF patients.

Conclusions: The smaller range of foraminal height and width in ACF patients at the operated level is consistent with the motion-limiting and motion-preserving nature of these surgeries. The smaller median foraminal height in ACF may be attributed to subsidence and the smaller intervertebral distance in ACF than in AD.[3, 4] The greater range of foraminal dimensions at nonoperated segments in ACF is consistent with the notion that motion lost at the fused level is compensated at nonoperated levels.

Patient Care: The foraminal dimension differences identified between ACDF and AD groups can help understand the mechanisms underlying the clinical efficacy of different surgical approaches and develop tools predictive of surgical outcome.

Learning Objectives: To our knowledge, this is the first in vivo comparison of 3D dynamic cervical foraminal dimensions between fusion and arthroplasty. The foraminal dimension differences identified between ACDF and AD groups can help understand the mechanisms underlying the clinical efficacy of different surgical approaches and develop tools predictive of surgical outcome. Prospective longitudinal studies are needed to evaluate the extent to which foraminal dimension measurements can be used for prognostic purposes.

References: [1] Liu, 2007, Spine, 32:2578. [2] McDonald, 2014, J Neurosurg Spine, 20: 245. [3] Lee, 2014, Spine 39:1280. [4] Komura, 2012, J Spinal Disord Tech, 25:23.