Abstract
ABSTRACT Objective Evaluate and compare the mechanical resistance and the fatigue behavior associated with the use of three different modalities of vertebral fixation system rod connectors through in vitro pre-clinical mechanical tests developed specifically for this application (linear, lateral with square connector and lateral with oblique connector). Methods Cobalt chromium rods 5.5 mm in diameter were used and coupled with three types of connectors: a) side rod with oblique connector, b) side rod with square connector, and c) rod and linear connectors. Quasi-static mechanical four-point bending and fatigue tests were performed. The variables measured were (I) the bending moment at the yield limit, (II) the displacement at the yield limit, (III) the rigidity of the system in flexion and (IV) the number of cycles until system failure. Results The linear system presented the greatest force and the greatest moment at the yield limit, as well as the greatest stiffness equivalent to bending. All specimens with square and oblique connectors endured 2.5 million cycles in the minimum and maximum conditions of applied moment. The specimens with linear connector endured 2.5 million cycles with fractions of 40.14% of the bending moment at the yield limit, but failed with levels of 60.17% and 80.27%. Conclusions Systems with linear connectors showed greater mechanical resistance when compared to systems with square and oblique connectors. All systems supported cyclic loads that mimic in vivo demands. Level of evidence V; In vitro research.
Highlights
Rigid, larger-diameter rods have been widely used in vertebral fixation systems for posterior spinal stabilization in recent decades
Evaluate and compare the mechanical resistance and the fatigue behavior associated with the use of three different modalities of vertebral fixation system rod connectors through in vitro pre-clinical mechanical tests developed for this application
The square and oblique connector systems showed no difference in maximum force, and both presented greater maximum force than the linear connector systems
Summary
Larger-diameter rods have been widely used in vertebral fixation systems for posterior spinal stabilization in recent decades. The rods have been used as connection components in vertebral fixation systems, usually coupled to the hooks or screws, which are the bone anchoring elements of these systems. This vertebral fixation modality has been widely used in the treatment of degenerative, tumoral, and traumatic diseases and deformities of the spine.[1]. The extension of the vertebral fixation can be performed by surgical exposure of the initially operated vertebral segment, removal of the rod, and its replacement with a longer rod Another technical option is the use of an additional rod connected to the rod of the primary vertebral fixation system. Connecting the rods allows the procedure to be performed with less morbidity, avoiding surgical exposure of the previously fixed vertebral segment.[2,3] The connection is used for multi-rod constructs, in which additional rods are used to increase biomechanical stability.[4]
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