Impact Of Connector Placement And Design On Bending Stiffness Of Spinal Constructs



Document Type



Objective: To evaluate the stability of multiple rod–connector construct designs using a mechanical 4-point bending testing frame. Methods: A mechanical study was used to evaluate the bending stiffness of 3 connectors across 12 different configurations of rod–connector–rod constructs. Stability was evaluated in flexion–extension and lateral bending. Combinations of rods having 1 of 3 diameters (4.0 mm, 5.5 mm, and 6.0 mm) connected by 1 of 3 connector types (parallel open, snap-on, and hinged) were compared. Configurations with single connectors and with double connectors with variable spacing were also compared to simulate revision surgery conditions. Results: Constructs consisting of 4.0-mm rods connected to 4.0-mm rods were significantly less stiff as the total number of connectors used in a series exceeded 2. When single-connector configurations were compared, parallel open rod connectors demonstrated greater stiffness in flexion–extension than hinged open connectors, whereas hinged open connectors demonstrated greater stiffness in lateral bending. Using double connectors increased stiffness of 4.0- to 4.0-mm rod configurations in flexion–extension and lateral bending, 4.0- to 6.0-mm rod configurations in flexion–extension, and 5.5- to 6.0-mm rod configurations in lateral bending. Spacing the double connectors significantly improved lateral bending stiffness of 4.0- to 4.0-mm and 5.5- to 6.0-mm rod configurations. Conclusions: Our data indicate that the design, number, and placement of rod connectors have a significant impact on the bending stiffness of a surgical construct. Such mechanical data may influence construct design in primary and revision surgeries of the cervical spine and cervicothoracic junction.

Publication Date


Publication Title

World Neurosurgery





First Page


Last Page


Digital Object Identifier (DOI)


This document is currently not available here.