The Biomechanical Effect of Transverse Connectors Use in a Pre- and Postlaminectomy Model of the Posterior Cervical Spine: An In Vitro Cadaveric Study

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Abstract

Study Design.

An in vitro biomechanical study investigating the effect of transverse connectors on posterior cervical stabilization system in a laminectomy model.

Objective.

To evaluate the optimal design, number, and location of the transverse connectors in stabilizing long segment posterior instrumentation in the cervical spine.

Summary of Background Data.

In the cervical spine, lateral mass screw (LMS) fixation is used for providing stability after decompression. Transverse connectors have been used to augment segmental posterior instrumentation. However, in the cervical region the optimal design, number, and the location of transverse connectors is not known.

Methods.

Seven fresh human cervicothoracic cadaveric spines (C2–T1) were tested by applying ±1.5 Nm moments in flexion (F), extension (E), lateral bending (LB), and axial rotation (AR). After testing the intact condition, LMS/rods were placed and then were tested with two different transverse connectors (top-loading connector [TL] and the head-to-head [HH] connector) in multiple levels, pre- and postlaminectomy (PL).

Results.

LMS significantly reduced segmental motion by 77.2% in F, 75.6% in E, 86.6% in LB, and 86.1% in AR prelaminectomy and by 75.4% in F, 76% in E, 80.6% in LB, and 76.4% in AR postlaminectomy compared to intact (P < 0.05). Only in AR, PL constructs with HH connectors at C3 & C7, TL connectors at C4–C5 & C5–C6, and at C3–C4 & C6–C7 significantly reduced the range of motion by 12.9%, 11.9%, and 11.9%, respectively, compared to PL LMS (P < 0.05). No statistical significance was observed between TL connector and HH connector in all loading directions.

Conclusion.

The biomechanical advantage of transverse connectors is significant in AR, when using two connectors at the proximal and distal ends, compared to one connector. In a clinical setting, this data may guide surgeons on transverse connector configurations to consider during posterior cervical instrumentation.

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