Biomechanical evaluation of posterior cervical stabilization after a wide laminectomy.
METHODS
In vitro biomechanical investigation with nondestructive and destructive testing in a human cadaveric model simulating a wide postlaminectomy condition.


OBJECTIVE
To determine the relative stability conferred by a posterior cervical spinal rod system and posterior cervical plating.


BACKGROUND
Posterior cervical plate fixation has been shown to be biomechanically superior to wiring techniques, but lateral mass screws may injure neurovascular structures or facet joints if they are inserted improperly. A cervical rod system has been developed to enhance the safety of lateral mass instrumentation.


METHODS
The cervical spines of 12 cadavers underwent biomechanical testing. After completion of the nondestructive intact testing, a wide laminectomy with subtotal facetectomies from C4 to C6 was performed. The specimens in two subgroups (group A, cervical spine rods with unicortical fixation, and group B, reconstruction plates with bicortical fixation) were tested in flexion, lateral bending, and torsion. Finally, destructive testing in flexion was performed. Stiffness, neutral zone, failure moment, energy to failure, and mechanism of failure were determined for each specimen. The data were analyzed using paired t tests and ANOVA.


RESULTS
Group B had a greater mean screw torque value. The instrumented constructs had a greater stiffness ratio (instrumented/intact) than the intact specimens in flexion, lateral bending, and torsional testing. Group A had a significantly greater flexural stiffness than Group B. Neutral zone ratio values were significantly lower during flexural testing for the cervical rod construct. Destructive testing resulted in significantly greater failure moment and energy-to-failure values for group A. In the cervical rod construct, failure occurred primarily by superior screw loosening with pull-out from the lateral mass. Reconstruction plates consistently failed with fracture of the lateral mass and superior screw loosening.


CONCLUSIONS
Significantly greater stability was noted in the cervical rod construct during nondestructive and destructive flexural testing.
Grubb
M R
MR
Department of Orthopaedics and Rehabilitation, Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, USA.
Currier
B L
BL
Stone
J
J
Warden
K E
KE
An
K N
KN
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001858:Bone Nails; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000502:physiology / Q000601:surgery*; D004867:Equipment Design; D006801:Humans; D016268:Internal Fixators; D007796:Laminectomy; D008875:Middle Aged; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical