Axis vertebral dimensions for safe screw placement: A CT normative data analysis

Area of Science:

• Neurosurgery
• Orthopedic Surgery
• Radiology

Background:

• Morphometric evaluation of the C2 vertebra is crucial for craniovertebral region surgery.
• Individual variations in C2 pedicle and isthmus dimensions necessitate population-specific data.
• Limited data exists for the Indian population regarding C2 morphometry.

Purpose of the Study:

• To measure average pedicle and isthmus dimensions of the C2 vertebra in an Indian population.
• To determine safe screw diameters for pedicle and transarticular screw placement in C2.
• To identify individuals at risk of neurovascular injury due to C2 anatomical variations.

Main Methods:

• CT scans of 100 Indian patients (18-70 years) were analyzed.
• Measurements included pedicle width, pedicle angle, internal height, and isthmic height.
• Anatomic suitability for transarticular and pedicle screw placement was assessed.

Main Results:

• Mean pedicle screw diameter: 4.99 mm (right), 5.20 mm (left).
• Mean transarticular screw diameter: 5.05 mm (right), 5.18 mm (left).
• 28% of pedicles and 22.5% of isthmuses were < 4.5 mm, potentially unsuitable for standard screws.

Conclusions:

• Pre-operative CT measurement is recommended to identify patients at risk of neurovascular injury.
• While most C2 vertebrae can accommodate 4 mm screws, variations necessitate caution.
• 28% of pedicles and 22.5% of isthmuses pose risks for standard screw placement.