This study analyzed cervical spine motion in 11 patients who underwent anterior cervical fusion surgery between the C5-C6 vertebrae. Motion analysis was performed using bi-planar fluoroscopy and clinical measures including neck disability, pain, and quality of life scores were assessed. During neck rotation, increased rotation between the C3-C4 vertebrae correlated with worse clinical outcomes, while increased rotation between C4-C5 correlated with better outcomes. The findings suggest that increased mobility at the level adjacent to the fusion site is healthier, while increased mobility two levels above may indicate a compensatory unhealthy state and potentially increased risk of adjacent segment disease.

1. In-vivo Three-dimensional Motion Analysis Correlated with Clinical Outcomes in 11 Cervical Fusion
Patients: A CNS Fellowship Funded Study
Victor Chang MD; Azam Basheer MD; Mokbel K. Chedid MD, FACS; Muwaffak Abdulhak MD; Stephen Bartol MD, MBA,
FACS; Michael Bey PhD; Colin McDonald MD
Henry Ford Hospital
Introduction
Anterior cervical fusion (ACDF) is a common
treatment of cervical spondylosis. Better
understanding of cervical motion post ACDF may
reveal which patients will progress to adjacent
segment disease (ASD).
Methods
11 patients who were 2 years post C5-6 ACDF
were enrolled for this study. Motion analysis was
performed using bi-planar fluoroscopy and a
model based tracking technique, accurate up to
0.6 mm and 0.6 degrees (1, 2). Clinical
measures were assessed using: Neck Disability
Index (NDI), Visual Analog Score (VAS) for arm
and neck pain, and the Short Form (36) Health
Survey physical component score (SF36).
Spearman’s method was used to measure
correlation between motion analysis parameters
and clinical scales.
Anatomical Coordinate System
Results
Inter-vertebral rotation was measured in 3 planes
(axial rotation, flexion/extension, lateral bending)
for neck rotation and extension. Mean NDI was
6±6.08, mean neck VAS was 0.75±1.1, mean
arm VAS 0.52±0.68, and mean SF36 was
44.55±10.11. During neck rotation, there was a
positive correlation with C3-4 axial rotation with
NDI (0.731, p=0.025), neck VAS (0.790,
p=0.011), and a negative correlation with SF36 (-
0.778, p=0.023). During neck extension, there
was a positive correlation with C3-4 extension
and neck VAS (0.685, p=0.042), and C4-5 lateral
bending with SF36 (0.743, p=0.035), with a
negative correlation with C4-5 lateral bending
with NDI (-0.714, p=0.031) and neck VAS (-0.896,
p=0.001).
Conclusions
Our analysis shows that increasing rotation at the
C3-4 level correlates with worsening clinical
outcome, and rotation at the C4-5 level correlates
with better clinical outcome after C5-6 ACDF.
This suggests that a mobile C4-5 segment is a
healthier state, and that increased mobility at C3-
4 indicates an unhealthy state, perhaps
compensatory for C4-5 immobility from
degeneration. These findings may help illustrate
the pathogenesis of ASD. Longitudinal follow-up
may also illustrate the natural history as well.
References
1. Bey MJ, Zauel R, Brock SK, et al. Validation of a new model-
based tracking technique for measuring three-dimensional, in vivo
glenohumeral joint kinematics. J Biomech Eng 2006;128:604-9
2. McDonald CP, Bachison CC, Chang V, et al. Three-dimensional
dynamic in vivo motion of the cervical spine: assessment of
measurement accuracy and preliminary findings. Spine J.
2010;10:497-504. Epub 2010 Apr 1
Learning Objectives
This study illustrates the following:
1) Three dimensional in-vivo motion analysis is
feasible in ACDF patients.
2) Correlations between clinical outcome and motion
analysis may establish “pathologic” movement that
may contribute to ASD.
3) Increased mobility at the rostral segment to
fusion was observed to correlate with better
outcome, while increased mobility 2 segments above
fusion was observed to correlate with worsening
outcome.
4) Further research and longitudinal follow-up will be
necessary to further illustrate the pathogenesis of
ASD.

2. Anatomical Coordinate System