A biomechanical testing protocol was used to evaluate atlantoaxial fixation techniques in a human cadaveric model.
To compare in vitro biomechanics of atlantoaxial lateral mass fusion cage combined with C1–C2 pedicle screw technique with those of C1–C2 pedicle screw technique alone and C1–C2 transarticular screws combined with Gallie wires.
An atlantoaxial lateral mass fusion cage was designed, knowing that the cage, when rigidly combined with C1–C2 pedicle screws, could offer other fusion spots for atlantoaxial stabilization in cases when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible. No comparative in vitro biomechanical test has been conducted previously to evaluate the feasibility of this method.
Anatomic measurements of the atlantoaxial lateral masses were taken using computed tomography in normal human subjects. Six fresh-frozen human cadaveric cervical spines (C0–C4) were used in the biomechanical study. Specimens were tested in their intact condition, after destabilization via transverse-alar-apical ligament disruption, and after implantation of 3 fixation constructs: (1) transarticular screws combined with Gallie wires, (2) C1–C2 pedicle screws, and (3) atlantoaxial lateral mass fusion cage combined with C1–C2 pedicle screws. Pure moment loading up to 1.5 Nm in flexion/extension, right-left lateral bending, and right-left axial rotation was applied to the occiput, and relative intervertebral rotations were determined using stereophotogrammetry. Range of motion for the intact, destabilized, and 3 fixation scenarios were determined.
The anatomic data indicated that feasible cage design were in 3 sizes: 11/8, 12/9, and 13/10 mm for length/width, and 3.5, 4, and 4.5 mm for height. The biomechanical data indicated that transverse-alar-apical ligament disruption significantly increased C1–C2 motion for all directions. All the 3 fixation techniques significantly reduced motion compared with the intact and destabilized cases. There were no statistically significant differences among the 3 fixation techniques.
The biomechanical study indicated that, contrary to expectation, addition of a cage did not increase the stability compared with C1–C2 pedicle screw alone. However, the C1 + C2 + Cage technique may be a viable alternative for atlantoaxial stabilization when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible.
A cadaver model was used to evaluate and compare the atlantoaxial stability afforded by a fusion cage, which was designed based on anatomic measurements of the atlantoaxial lateral masses, combined with C1–C2 pedicle screws technique with C1–C2 pedicle screw technique alone and Magerl-Gallie technique. No statistically significant differences were found among the 3 stabilization methods.
From the *Department of Orthopedics, Changzheng Hospital, The Second Military Medical University, Shanghai, China; and †Institute of Clinical Anatomy and Biomechanics, Southern Medical University, Guangzhou, China.
Acknowledgment date: April 6, 2009. First Revision date: October 11, 2009. Second Revision date: July 12, 2009. Acceptance date: September 12, 2009.
The device(s)/drug(s) that is/are the subject of this manuscript is/are not FDA-approved for this indication and is/are not commercially available in the United States.
No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
Address correspondence and reprint requests to Bin Ni, MD, Department of Orthopedics, Changzheng Hospital, The Second Military Medical University, 415 Fengyang Road, Huangpu District, Shanghai 200003, People's Republic of China; E-mail: email@example.com