Feasibility and Safety of the C1 “Zero Angle” Screw: A Novel “In–Out–In” Technique for Atlantoaxial Dislocation

Orthopaedic Surgery, 2025 · DOI: 10.1111/os.14309 · Published: January 1, 2025

Simple Explanation

This study introduces a new surgical technique called the C1 “Zero Angle” screw (C1ZAS) with an “in-out-in” approach for treating atlantoaxial dislocation (AAD), a condition where the top two vertebrae in the neck are misaligned. The C1ZAS technique aims to provide a more stable and secure fixation of the vertebrae, especially in cases where the standard screw placement is difficult due to anatomical constraints or previous surgeries. The study evaluates the safety and effectiveness of this new technique by analyzing radiological measurements and clinical outcomes in a group of patients who underwent the procedure.

Study Duration

January 1, 2022 and December 31, 2023

Participants

61 patients with AAD or atlantoaxial instability

Evidence Level

Not specified

Key Findings

1
The C1ZAS technique, using an “in-out-in” approach, is a feasible alternative to C1 pedicle screw (PS) placement, particularly in patients with AAD and narrow C1 pedicles.
2
Radiographic measurements indicate that the C1ZAS technique provides sufficient space for screw placement while minimizing the risk of vertebral artery or dural injury.
3
Clinical outcomes in a small group of patients showed satisfactory C1ZAS placement, atlantoaxial reduction, and improved neurological function without instances of implant failure or vascular/dural complications.

Research Summary

The study introduces and evaluates the C1ZAS technique with an “in-out-in” approach as an alternative to C1 PS placement for AAD patients, especially those with narrow C1 pedicles. The radiographic and clinical results suggest that the C1ZAS technique is feasible and safe, providing adequate screw purchase and minimizing the risk of complications. The authors conclude that C1ZAS can be considered as an efficient alternative option when the placement of C1 PS is prohibited due to anatomical constraints.

Practical Implications

Surgical Technique

The C1ZAS technique provides surgeons with an alternative method for achieving stable fixation in AAD cases where traditional screw placement is challenging.

Patient Selection

The study helps identify patients with AAD and narrow C1 pedicles who may benefit from the C1ZAS technique.

Risk Reduction

The C1ZAS technique minimizes the risk of vertebral artery injury and dural laceration during AAD surgery.

Study Limitations

1
The study has a small sample size, limiting the generalizability of the findings.
2
It is a retrospective single-center study, requiring further validation through multicenter studies with larger samples and long-term follow-up.
3
MRI parameters may not be as accurate as CT scans for assessing bone cortex, which could affect the precision of measurements.

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