Anterior occiput to axis screw fixation: part II: a biomechanical comparison with posterior fixation techniques.
METHODS
This biomechanical study used flexibility testing on fresh-frozen human cadaveric specimens (occiput to C3) and compared the range of motion and neutral zone for three occipitocervical fixation techniques.


OBJECTIVE
To contrast the stabilization provided by a new technique of anterior occipitocervical screw fixation with two other commonly used posterior occipitocervical fixation techniques.


BACKGROUND
There are no published reports describing this novel technique of anterior occipitocervical screw fixation.


METHODS
Six human occipitocervical spine specimens were mounted in a custom-designed, spine-testing machine that applied a pure moment in flexion-extension, lateral bending, and axial rotation. The specimens were tested intact, after an odontoid osteotomy with capsular injury, and after each of three fixation methods: posterior wiring, posterior plate fixation with C1-C2 transarticular screws, and finally with anterior occipitocervical screws. Intervertebral motion was measured with an optoelectronic measurement system, and the range of motion and neutral zone were the kinematic variables measured and used for analysis.


RESULTS
In flexion and extension testing, the posterior plate with transarticular screws provided greater stabilization than posterior wiring or anterior occipitocervical screws. In lateral bending and rotation, the anterior screws were similarly effective to the posterior plate, both of which were more effective than posterior wiring.


CONCLUSIONS
The anterior screw fixation technique was as effective as a posterior plate with transarticular screws in stabilizing between the occiput and C2 in axial rotation and lateral bending. In extension and flexion, the anterior screw technique was not as effective as a posterior plate with transarticular screws in providing stability.
Dvorak
Marcel F S
MF
Division of Spine, Department of Orthopaedics, University of British Columbia and the Combined Neurosurgical and Orthopaedic Spine Program, Vancouver Hospital and Health Sciences Centre, Canada. mdvorak@vanhosp.bc.ca
Sekeramayi
Floyd
F
Zhu
Qingan
Q
Hoekema
Joel
J
Fisher
Charles
C
Boyd
Mike
M
Goertzen
Darrell J
DJ
Oxland
Thomas R
TR
D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging / Q000601:surgery*; D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D016268:Internal Fixators; D008422:Materials Testing; D009777:Occipital Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D018583:Pliability; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing / Q000502:physiology