Anterior cervical fusion: a biomechanical comparison of 4 techniques. Laboratory investigation.
OBJECTIVE
Cervical instrumented fusion is currently performed using several fixation methods. In the present paper, the authors compare the following 4 implantation methods: a stand-alone cage, a cage supplemented by an anterior locking plate, a cage supplemented by an anterior dynamic plate, and a dynamic combined plate-cage device. METHODS Four finite element models of the C4-7 segments were built, each including a different instrumented fixation type at the C5-6 level. A compressive preload of 100 N combined with a pure moment of 2.5 Nm in flexion, extension, right lateral bending, and right axial rotation was applied to the 4 models. The segmental principal ranges of motion and the load shared by the interbody cage were obtained for each simulation.


RESULTS
The stand-alone cage showed the lowest stabilization capability among the 4 configurations investigated, but it was still significant. The cage supplemented by the locking plate was very stiff in all directions. The 2 dynamic plate configurations reduced flexibility in all directions compared with the intact case, but they left significant mobility in the implanted segment. These configurations were able to share a significant part of the load (up to 40% for the combined plate-cage) through the posterior cage. The highest risk of subsidence was obtained with the model of the stand-alone cage.


CONCLUSIONS
Noticeable differences in the results were detected for the 4 configurations. The actual clinical relevance of these differences, currently considered not of critical importance, should be investigated by randomized clinical trials.
Galbusera
Fabio
F
LaBS, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy. fabio.galbusera@polimi.it
Bellini
Chiara M
CM
Costa
Francesco
F
Assietti
Roberto
R
Fornari
Maurizio
M
D001696:Biomechanical Phenomena; D001860:Bone Plates; D002574:Cervical Vertebrae; D020342:Finite Element Analysis; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability / Q000601:surgery*; D008954:Models, Biological; D016059:Range of Motion, Articular; D013122:Spinal Diseases / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D016474:Weight-Bearing