Preliminary biomechanical proof of concept for a hybrid locking plate/variable pitch screw construct for anterior fixation of type II odontoid fractures.
METHODS
A human cadaveric biomechanical proof-of-concept study.


OBJECTIVE
To test whether adding a locking plate to the anterior surface of C2 attaching directly to the interfragmentary screw may reduce potential for anterior screw cutout and improve construct strength.


BACKGROUND
The most common mode of failure for screw fixation of dens fractures is via cutout at the anterior body of C2.


METHODS
A human, cadaveric model of type II dens fractures was created and fixed using either a headless, fully threaded variable pitch screw (FTVPS) or a screw with an attachable locking plate construct (LPC). Following quasistatic loading to failure, stiffness and load to failure were compared using t tests. Mode of failure was determined from radiographical and gross inspection.


RESULTS
Load to failure was greater for the LPC than for the FTVPS alone (498 N vs. 362 N, P = 0.04). The LPC consistently failed via compression of cancellous bone posterior to the lag screw, whereas the FTVPS constructs failed via cutout of the screw from the anterior C2 body.


CONCLUSIONS
Locking plate supplementation of anterior screw fixation of type II odontoid fractures improves construct strength and changes the failure mechanism from anterior screw cutout to posterior displacement of the screw. An attachable locking plate/interfragmentary screw construct may improve clinical outcomes for these fractures.
Department of Orthopaedics, Brown University Warren Alpert School of Medicine, Providence, RI, USA.
Alan H
AH
Daniels
William
W
Magee
Mohammed
M
Badra
Brian
B
Bay
Werner
W
Hettwer
Robert A
RA
Hart
D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D015519:Bone Density; D001860:Bone Plates; D001863:Bone Screws; D004867:Equipment Design; D004868:Equipment Failure; D005260:Female; D005593:Fracture Fixation, Internal; D006801:Humans; D008297:Male; D008875:Middle Aged; D009809:Odontoid Process / Q000293:injuries* / Q000601:surgery; D016103:Spinal Fractures / Q000601:surgery*; D016474:Weight-Bearing