An in vitro cadaveric biomechanical study.
To determine the stability of translaminar screws compared to pedicle screws at T1–T2 for constructs bridging the cervicothoracic junction.
Summary of Background Data.
Instrumented fixation of the cervicothoracic junction is challenging both biomechanically, due to the transition from the mobile cervical to the rigid thoracic spine, and technically, due to the anatomic constraints of the T1–T2 pedicles. For these reasons, an alternate fixation technique at T1–T2 that combines ease of screw insertion and a favorable safety profile with biomechanical stability would be clinically beneficial.
A 6-degree of freedom spine simulator was used to test multidirectional flexibility in 8 human cadaveric specimens. Flexion, extension, lateral bending, and axial rotation were tested in the intact condition, followed by destabilization via a simulated 2-column injury at C7–T1. Specimens were reconstructed using C5–C6 lateral mass screws and either translaminar or pedicle screws placed at T1, followed by caudal extension to T2. A 3-column injury at C7–T1 was then performed and specimens were tested using a posterior only approach with either translaminar or pedicle screws placed at T1 and T1–T2. Finally, anterior fixation at C7–T1 was added and multidirectional flexibility testing performed as previously described.
Following a 2-column injury at C7–T1, there were no significant differences in segmental flexibility at C7–T1 between translaminar and pedicle screw fixation when placed at T1–T2 (P > 0.05). For a 3-column injury treated posteriorly, translaminar screws at T1–T2 provided increased flexibility compared to pedicle screws in flexion/extension (P < 0.05). There were no differences in segmental flexibility at C7–T1 between the 2 techniques following the addition of anterior fixation (P > 0.05).
Translaminar screws in the upper thoracic spine offer similar stability to pedicle screw fixation for constructs bridging the cervicothoracic junction. Small differences in range of motion must be weighed clinically against the potential benefits of translaminar screw insertion at T1–T2.