Pars interarticularis screws for posterior cervical fusion – investigating a new trajectory using a CT‑based multiplanar reconstruction: Part I

Acta Neurochirurgica, 2024 · DOI: https://doi.org/10.1007/s00701-024-06184-x · Published: July 11, 2024

Simple Explanation

This study introduces a novel screw trajectory through the pars interarticularis for posterior cervical fusion, offering a potential alternative to traditional lateral mass screw fixation. The novel trajectory aims to ease in-line instrumentation of both lateral mass screws (LMS) and cervical pedicle screws (CPS), potentially serving as a salvage strategy for failed LMS. Two trajectories were analyzed: Trajectory A (upper outer quadrant entry, horizontal trajectory) and Trajectory B (lower outer quadrant entry, cranially pointed trajectory), compared against standard LMS and CPS trajectories.

Study Duration

January to July 2018

Participants

10 patients (gender 1:1 distribution)

Evidence Level

Not specified

Key Findings

1
Trajectory B demonstrated significantly longer pars lengths (15.69 ± 0.65 mm) compared to Trajectory A (12.51 ± 0.24 mm; p < 0.01).
2
Lateral mass screw lengths were comparable to pars interarticularis screw lengths using Trajectory B.
3
Both trajectories provided safe angular ranges, minimizing the risk to delicate structures such as the spinal cord and vertebral artery.

Research Summary

The study investigates a novel pars interarticularis screw trajectory as a potential alternative to lateral mass screws for posterior cervical fusion, especially in minimally invasive surgery (MISS) contexts. Trajectory B, with a lower outer quadrant entry and cranial direction, shows promise as a feasible and safe alternative, reducing risks to the vertebral artery and spinal cord. Preoperative assessment and intraoperative technologies are crucial for successful implementation, and biomechanical validation is necessary before clinical application.

Practical Implications

Minimally Invasive Surgery

Pars interarticularis screws, especially with Trajectory B, may facilitate minimally invasive posterior cervical fusion by offering a more lateral entry point, reducing the need for extensive muscle dissection.

Reduced Neurovascular Risk

The novel trajectories aim to minimize the risk of vertebral artery and spinal cord injury, potentially improving patient safety during posterior cervical fusion.

In-Line Instrumentation

Pars interarticularis screws can ease the alignment and connection of lateral mass screws and cervical pedicle screws in multilevel constructs, simplifying the surgical procedure.

Study Limitations

1
The study was solely an imaging study and may not reflect the intraoperative anatomical conditions appropriately.
2
Individual anatomical abnormalities and variations may not be fully considered due to the limited number of patients.
3
Biomechanical studies are mandatory before clinical application to validate the feasibility and safety of the new trajectories.

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