In vitro biomechanical evaluation of four fixation techniques for distractive-flexion injury stage 3 of the cervical spine.
OBJECTIVE
Anterior plate fixation has been reported to provide satisfactory results in cervical spine distractive flexion (DF) injuries stages 1 and 2, but will result in a substantial failure rate in more unstable stage 3 and above. The aim of this investigation was to determine the biomechanical properties of different fixation techniques in a DF-3 injury model where all structures responsible for the posterior tension band mechanism are torn.


METHODS
The multidirectional three-dimensional stiffness of the subaxial cervical spine was measured in eight cadaveric specimens with a simulated DF-3 injury at C5-C6, stabilized with four different fixation techniques: anterior plate alone, anterior plate combined with posterior wire, transarticular facet screws, and a pedicle screw-rod construct, respectively.


RESULTS
The anterior plate alone did not improve stability compared to the intact spine condition, thus allowing considerable range of motion around all three cardinal axes (p > 0.05). The anterior plate combined with posterior wire technique improved flexion-extension stiffness (p = 0.023), but not in axial rotation and lateral bending. When the anterior plate was combined with transarticular facet screws or with a pedicle screws-rod instrumentation, the stability improved in flexion-extension, lateral bending, and in axial rotation (p < 0.05).


CONCLUSIONS
These findings imply that the use of anterior fixation alone is insufficient for fixation of the highly unstable DF-3 injury. In these situations, the use of anterior fixation combined with a competent posterior tension band reconstruction (e.g. transarticular screws or a posterior pedicle screws-rod device) improves segmental stability.
Stockholm Spine Center, Löwenströmska Hospital , Upplands Väsby , Sweden.
Thomas
T
Henriques
Bryan W
BW
Cunningham
Paul C
PC
McAfee
Claes
C
Olerud
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D001864:Bone Wires; D002574:Cervical Vertebrae / Q000293:injuries* / Q000503:physiopathology / Q000601:surgery; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*; D016059:Range of Motion, Articular; D013124:Spinal Injuries / Q000601:surgery*
Biomechanical analysis; cervical spine; distractive–flexion injury; internal fixation; pedicle screws; transarticular screws