A new stand-alone anterior lumbar interbody fusion device: biomechanical comparison with established fixation techniques.
METHODS
Established lumbar fixation methods were assessed biomechanically, and a comparison was made with a new stand-alone anterior lumbar interbody cage device incorporating integrated anterior fixation.


OBJECTIVE
To compare the stability of a new stand-alone anterior implant (Test-device) with established fixation methods to assess its suitability for clinical use. Our hypothesis being that the Test-device would provide stability comparable to that provided by an anterior cage when supplemented with posterior pedicle screw fixation.


BACKGROUND
It is accepted that the use of rigid pedicle screw instrumentation increases the chance of achieving a solid fusion, but its use may be associated with a significant increase in postoperative morbidity caused by disruption of the posterior musculature. It is also evident that this increased fusion rate is generally not associated with increased clinical success. This dilemma has led to a search for a solution and to the development of the Test-device anterior lumbar interbody device.


METHODS
The kinematic properties of either the L3-L4 or L4-L5 lumbar motion segment of 8 cadaveric lumbar spines have been tested using the following sequence of fixation: intact, Test-device, Test-device and translaminar facet screws (TS), Cage and TS, Cage and Universal Spine System (USS), and Cage and small stature USS.


RESULTS
All fixation techniques except the cage and TS decreased (P < 0.05) range of motion (ROM), neutral zone (NZ), and elastic zone (EZ), and increased (P < 0.05) stiffness in comparison to the intact motion segment in all test modes. There was a significant increase (P < 0.01) in the ROM, NZ, and EZ, and decrease in the stiffness of the cage and TS group in comparison to all other stabilization techniques in flexion and rotation. There was no significant difference in the ROM, NZ, EZ, and stiffness between the Test-device and cage and USS groups in flexion, extension, and bending. The Test-device resulted in a significantly lower EZ (P < 0.05) and a significantly higher stiffness (P < 0.05) in rotation than all other fixation methods.


CONCLUSIONS
The Test-device alone provided similar and the Test-device and TS higher stability than the pedicle screw constructs evaluated. These results support progression to clinical trials using the Test-device as a stand-alone implant.
Cain
Christopher M J
CM
Adelaide Spine Clinic, Adelaide, Australia. drcmjcain@adelaide.on.net
Schleicher
Philip
P
Gerlach
Rene
R
Pflugmacher
Robert
R
Scholz
Matti
M
Kandziora
Frank
F
D000328:Adult; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods; D001863:Bone Screws / Q000592:standards; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D016268:Internal Fixators / Q000592:standards; D007403:Intervertebral Disc / Q000502:physiology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009984:Orthopedic Fixation Devices / Q000592:standards; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods