Pedicle screw motion in the osteoporotic spine after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement: a comparative analysis.
METHODS
A biomechanical study addressing the motion of pedicle screws in a human cadaveric, osteoporotic spine model.


OBJECTIVE
To compare the fixation of pedicle screws in an osteoporotic spine model after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement and to determine the kinematic patterns of these screws.


BACKGROUND
Numerous techniques exist for improving the quality of fixation within the osteoporotic spine, including supplementing the construct with laminar hooks, sublaminar wires, or calcium phosphate cement. Direct comparisons of these practices, however, are lacking. METHODS.: Twenty-four cadaveric lumbar vertebrae were instrumented with a pedicle screw and rod construct augmented with laminar hooks, sublaminar wires, or calcium phosphate cement. The screws were tested cyclically with physiologic loads. Rigid body motions of the screws were measured using an optoelectronic camera system, and the motion at the screw tip and at the screw head were calculated. Screw motions were compared using nonparametric paired statistical analysis.


RESULTS
Between augmentation groups, there were no significant differences in the magnitude of motion at the screw head and at the screw tip. After calcium phosphate cement supplementation, screw motion was predominantly rotational in nature, whereas rigid body translation of the screw was more common with sublaminar wires or laminar hooks.


CONCLUSIONS
The three augmentation techniques were similar in their ability to enhance the rigidity of fixation of the pedicle screws. Differences did exist, however, in the patterns of pedicle screw motion, with the calcium phosphate cement augmentation resulting in less rigid body translation than the other two techniques.
Department of Mechanical Engineering, University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, British Columbia, Canada.
Juay-Seng
JS
Tan
Brian K
BK
Kwon
Marcel F
MF
Dvorak
Charles G
CG
Fisher
Thomas R
TR
Oxland
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D001863:Bone Screws; D001864:Bone Wires; D002102:Cadaver; D002484:Cementation; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000379:methods*; D010024:Osteoporosis / Q000601:surgery*; D016059:Range of Motion, Articular; D013122:Spinal Diseases / Q000601:surgery*