Authors of section

Author

Jean Ouellet

General Editor

Luiz Vialle

Open all credits

Insertion of iliac screw

1. Screw entry points

There are two standard iliac screw starting points within the ilium and one within the sacrum.

insertion of iliac screw

2. Traditional entry point

The traditional entry point is in the posterior iliac crest and countersunk to prevent pressure ulcers over the implant.

insertion of iliac screw

An oscillating drill (3.5 mm) or awl is used to penetrate between the two cortices in a ventral, caudal direction toward the anterior inferior iliac spine.

When resistance is felt, the length is measured for the insertion of the pedicle screw.

The preferred diameter is 7.0 or 8.0 mm.

insertion of iliac screw

3. Second starting point

Second iliac starting point is referred to as anatomic starting point. It is more caudal and medial than the traditional starting point and aligns better with the lumbar pedicles.

The more caudal position places this screw in a wider cross section of bone above the sciatic notch

insertion of iliac screw

An oscillating drill (3.5 mm) or awl is used to penetrate between the two cortices in a ventral, caudal direction toward the anterior inferior iliac spine.

When resistance is felt, the length is measured for the insertion of the pedicle screw.

The preferred diameter is 7.0 or 8.0 mm.

insertion of iliac screw

4. Third starting point

The third starting point is at the inferolateral aspect of the S1 foramen.

insertion of iliac screw

An oscillating drill (3.5 mm) or awl is used to cross the sacroiliac joint and penetrate between the two cortices of the ilium in a ventral, caudal direction towards the anterior inferior iliac spine.

When resistance is felt, the length is measured for the insertion of the pedicle screw.

The preferred diameter is 7.0 or 8.0 mm.

Because a more lateral trajectory is required, the screws placed using this technique tend to be shorter than those with an iliac starting point.

As the starting point is deeper, there is less concern with screw prominence compared to iliac starting points.

Because the screw crosses the sacroiliac joint, there is potential for long term consequences such as arthrosis and pain.

insertion of iliac screw

5. Screw trajectory and imaging

The true lateral view (with sciatic notches superimposed) is the primary view for screw insertion.

insertion of iliac screw

Screw trajectory should extend within 2 cm above the sciatic notch, above the acetabulum and towards the anterior inferior iliac spine.

insertion of iliac screw

The obturator outlet (teardrop) view provides a cross sectional view of the tear drop shaped bony channel above the sciatic notch within which the screw should be positioned.

insertion of iliac screw

The screw should be confined to the bony margins of the tear drop on the obturator outlet view.

insertion of iliac screw

6. Additional views

Obturator inlet view

This view is perpendicular to the screw trajectory. The screw should remain within the inner and outer margins of the ilium.

insertion of iliac screw

Iliac oblique view

This view is perpendicular to the ilium and can be used to verify screw position above the sciatic notch and acetabula, and acceptable screw length.

insertion of iliac screw