July 18, 2024

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 method, Magerl method and Weinstein method for fixation of lumbar spine

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

Magerl, Roy-Camille and Modified techniques for cervical spine fixation

Thoracic screws entry point

Pedicle screw fixation for cervical spine

Artery of adamkewicz should always be considered during thoracic surgery