Mechanical comparison of posterior instrumentation constructs for spinal fixation across the cervicothoracic junction.
METHODS
A biomechanical study comparing 4 different posterior implant configurations for instrumentation across the cervicothoracic junction.


OBJECTIVE
To compare mechanical parameters during flexion bending and axial rotation testing among 4 different posterior cervicothoracic rod-and-screw constructs.


BACKGROUND
Several posterior rod constructs are available for instrumentation across the cervicothoracic junction. No studies have examined the mechanical properties of constructs of varying rod diameters and rod connector types.


METHODS
Four different rod-and-screw-based constructs for posterior cervicothoracic instrumentation underwent flexion bending or axial rotation testing. Stiffness, ultimate and yield forces (torques) were compared using an analysis of variance.


RESULTS
Significantly lower stiffness, ultimate and yield force (torque) was observed with a 3.5-mm rod construct compared with the 3 other constructs. No significant differences were demonstrated between a dual diameter rod (3.5 mm to 5.5 mm) and a solid domino connector extending between 3.5-mm and 5.5-mm rods. A hinged domino connector construct between 3.5-mm and 5.5-mm rods had similar stiffness but lower ultimate and yield force from either the dual diameter rod or the solid domino construct.


CONCLUSIONS
The present results demonstrate that the 3.5-mm rod-and-screw construct is the weakest configuration for posterior fixation across the cervicothoracic junction. The dual diameter rod and fixed domino connector constructs were the strongest and demonstrated similar values for yield and ultimate force.
Tatsumi
Robert L
RL
Department of Orthopaedics and Rehabilitation, Oregon Health & Sciences University, Portland, OR 97239, USA.
Yoo
Jung U
JU
Liu
Qi
Q
Hart
Robert A
RA
D001858:Bone Nails; D001863:Bone Screws; D008422:Materials Testing; D011475:Prosthesis Failure; D013123:Spinal Fusion / Q000295:instrumentation*; D013904:Thoracic Vertebrae; D019415:Torque; D014102:Torsion Abnormality; D016474:Weight-Bearing