Pedicle screws are used in spinal surgery to provide stabilization and support following fractures or fusion surgeries. They are used for fixation in the spine. Different methods of insertion of those screws are discussed in this note.
Why pedicle screws?
- Strongest hold of vertebrae
- Very strong fixation
- Fixing all 3 columns
A bilateral grip allows manipulations and rotations in all directions
Techniques of pedicle screws fixation
Patient positioning
- Directions of the pedicle in all planes
Excellent exposure
- Ideally to tip of transverse process
- Visualize entry point clearly
Study Xrays/ CT scan
Size of pedicle screws as per location:
Thoracic: 4-5 mm
Lumbar: 5-6 mm
Sacral: 7mm
The different surgical approaches can be used for fixation, most commonly being anterior for the cervical and posterior for the lumbar spine.
Determine Entry Point for screws (Lumbar):
Should be intraosseous placement
Roy- Camille Intersection:
The intersection of mid transverse process line and mid facet line
Magerl Method:
Junction of the lateral edge of the superior facet and mid-transverse line
Weinstein :
Lateral and inferior corner of superior facet joint
Trajectory:
If the entry point is lateral (to save facet joint)
Lateral to medial:
- Convergence
- Assistance of spinous process
If the entry point is medial (through facet )= Straight entry
Superior to inferior:
- Should not hit the upper-end plate
- Target subchondral placement
- Assistance to lateral x-ray
Length of pedicle screw:
- Should not hit anterior wall
- Should end in 2/3rd of anterior body
Important Relations:
Inferior: Nerve Root
Medial : Dura ( Spinal cord)
Anterior : Vessels
Cervical Lateral mass entry point for screws
Magerl Entry Point:
Divide lateral mass into 4 equal quardents and screw is inserted slightly supero-medially to insertion of these points
Screws are kept parallel to facet joint
Roy- Camille Technique:
Entry point is central –>Go straight and more laterally
Thoracic screws entry point
Artery of adamkewicz should always be considered during thoracic surgery