Stability analysis of craniovertebral junction fixation techniques.
BACKGROUND
Craniovertebral arthrodesis in the upper cervical spine is challenging because of the high degree of mobility afforded by this region. A novel method for achieving atlantoaxial fixation with use of polyaxial screws inserted bilaterally into the lateral masses of C1 and transpedicularly into C2 with longitudinal rod connection has recently been introduced. The question remains as to whether this technique provides adequate stability when extended cephalad to include the occiput. The purpose of this study was to determine the primary stability afforded by this novel construct and compare its stability with the current standard of bilateral longitudinal plates combined with C1-C2 transarticular screws.


METHODS
We used ten fresh-frozen human cadaveric cervical spines (C0-C4). Pure moment loads were applied to the occiput, and C4 was constrained during the testing protocol. We evaluated four conditions: (1) intact, (2) destabilized by means of complete odontoidectomy, (3) stabilization with longitudinal plates with C1-C2 transarticular screw fixation, and (4) stabilization with a posterior rod system with C1 lateral mass screws and C2 pedicle screws. Rigid-body three-dimensional rotations were detected by stereophotogrammetry by means of a three-camera system with use of marker triads. The range of motion data (C0-C2) for each fixation scenario was calculated, and a statistical analysis was performed.


RESULTS
Destabilization of the specimen significantly increased C0-C2 motion in both flexion-extension and lateral bending (p < 0.05). Both fixation constructs significantly reduced motion in the destabilized spine by over 90% for all motions tested (p < 0.05). No significant differences were detected between the two constructs in any of the three rotational planes.


CONCLUSIONS
Both hardware systems provide equivalent construct stability in the immediate postoperative period when it is critical for the eventual success of a craniovertebral arthrodesis. On the basis of this work, we believe that the decision to use either construct should be determined by clinical rather than biomechanical concerns.
Department of Orthopaedic Surgery, University of California at San Francisco, 1001 Potrero Avenue, Room 3A36, San Francisco, CA 94110, USA. puttlit@itsa.ucsf.edu
Christian M
CM
Puttlitz
Robert P
RP
Melcher
Frank S
FS
Kleinstueck
Juergen
J
Harms
David S
DS
Bradford
Jeffrey C
JC
Lotz
D000368:Aged; D000704:Analysis of Variance; D001174:Arthrodesis / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D001269:Atlanto-Occipital Joint; D001696:Biomechanical Phenomena; D001860:Bone Plates / Q000592:standards; D001863:Bone Screws / Q000592:standards; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D008422:Materials Testing; D009809:Odontoid Process / Q000601:surgery; D010027:Osteotomy / Q000379:methods; D018579:Patient Selection; D016059:Range of Motion, Articular; D012399:Rotation; D013718:Tensile Strength; D016896:Treatment Outcome