A kinematic study of the cervical spine before and after segmental arthrodesis.
METHODS
The acute kinematic consequence of segmental arthrodesis in the cervical spine on the remaining open motion segments was studied in a cadaveric model.


OBJECTIVE
To evaluate the distribution of motion across unfused cervical motion segments after a segmental arthrodesis. The applied load was determined as a function of arthrodesis length and level by using a fixed range of motion for the cervical spine (C2-T1).


BACKGROUND
An increased incidence of degenerative disease may exist at the levels immediately adjacent to a cervical arthrodesis as a result of alteration in biomechanical behavior at these levels.


METHODS
One-, two-, and three-level fusions were simulated in multilevel ligamentous human cervical spines. Specimens were tested nondestructively through a 30 degrees range of sagittal plane rotation. Motion was recorded using three-dimensional stereophotogrammetry. Sagittal plane rotation of each motion segment in the fusion models was compared with the corresponding rotation in the unfused specimen.


RESULTS
In the C2-C4 fusion, the increase in motion at C5-C6 was statistically less (P < 0.05) than the increase at C7-T1. In the C2-C5 fusion, the increase in motion at C5-C6 was statistically less (P < 0.05) than the increases at C6-C7 and C7-T1. For each of the five other fusion types tested, no statistical differences existed between the increases in sagittal rotation at any of the open motion segments. The bending moment necessary to produce 30 degrees of sagittal rotation increased nonlinearly as the number of motion segments fused increased.


CONCLUSIONS
Under what was considered a realistic loading paradigm, sagittal plane rotation was not increased disproportionately at the motion segments immediately adjacent to a segmental arthrodesis in the cervical spine. The nonlinear rise in applied bending moment to achieve constant displacement was characteristic of the behavior of the ligaments and intervertebral discs throughout the spine as they underwent increasing deformation.
Fuller
D A
DA
Department of Orthopaedics, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Kirkpatrick
J S
JS
Emery
S E
SE
Wilber
R G
RG
Davy
D T
DT
D000368:Aged; D002102:Cadaver; D002574:Cervical Vertebrae / Q000502:physiology* / Q000601:surgery*; D006801:Humans; D010780:Photogrammetry; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013123:Spinal Fusion; D013314:Stress, Mechanical