Objective. To compare the immediate stable efficacy and load sharing effect of two types of
anterior cervical screw-plating instrumentations: the Morscher Synthes titanium locking
screw-plate system and the Caspar trapezoidal screw-plate system.
Design. Fresh porcine cervical spines with intact, two surgery unstable models, and then
reconstructed with or without screw-plating instruments were compared in three physiological
Background. Two markedly instrumentation systems––Morscher Synthes titanium cervical locking
screw-plate and Caspar trapezoidal screw-plate systems are commonly used in management
of complex cervical spine disorders. Although the biomechanical study showed that
the lower cost Caspar system performed superior in extension before and after plate
fatigue, the clinic evaluations of two systems were contradictory. So (1) does the
titanium cervical locking plate system pay for its higher cost? and (2) what is the
load sharing character of strut graft in one level corpectomy?
Methods. Eight fresh ligamentous porcine cervical spines from C3 to C7 were undergone axial
compression, rotation and sagittal flexion tests. The biomechanical experiment was
sequentially repeated for the intact, C5-6 discectomy, C5 corpectomy, and then stabilized
by either type of plate fixation devices with or without polymethylmethacrylate bone
cement grafting. Strains measured by an extensometer across the operated motion segment
were used as the index of stability.
Results. Analysis of the strain data showed both types of anterior fixation plate systems
provided adequate-restored stability for the spinal column only aided with polymethylmethacrylate
construction. Statistically, there was no significant difference in biomechanical
evaluation for the stability effect between much cost Morscher Synthes plate and Caspar
plate system (p<0.005). The spinal disc bore as much as 75% of axial loading. While the strut graft
functioned as the disc substitute and spacer, it bore more than 90% of axial loading.
In high degree of flexion, the transmitted compressive load was shifted anteriorly
to the screw-plate. This might unload the polymethylmethacrylate graft and resulted
in the strut graft in tensile fatigue failure.
Conclusions. Statistically both systems showed similar stable efficacy, however, the Morscher
Synthes cervical locking plate system might provide better stable effect in higher
degrees of flexion motion. The strut graft played as the major load-bearing role in
axial compression and sagittal flexion, while in axial rotation, the applied torque
was mainly resisted by facet joint and screw-plate system complex.Relevance
The minor discrepancy of two plating systems may be due to the nature of plate geometry
and design but not the material properties. Combination of bone graft and either plating
systems provides adequate fusion stability under physiological loadings. The high
degree flexion may cause the posterior portion of polymethylmethacrylate graft in
tensile fracture and then result in polymethylmethacrylate failure in clinic observation.