Authors of section

Authors (on behalf of the AOSpine Knowledge Forum Tumor)

Nicolas Dea, Jeremy Reynolds

General Editor

Luiz Vialle

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S1 pedicle screw insertion

1. Preparation

Once the spine is exposed, the appropriate levels of fixation are confirmed with the image intensifier.

2. Entry points

The entry point of the pedicle screw is defined by the inferior border of the superior facet of S1.

Modify entry point to match image below

3. Opening of cortex

Open the superficial cortex of the entry point with a burr or a rongeur.

Opening of cortex during S1 pedicle screw insertion

4. Medio-lateral inclination

The trajectory of the screw is 30° medially.

Medio-lateral inclination of S1 pedicle screw

5. Cranial-caudal angulation

A pedicle probe is used to navigate down the isthmus of the pedicle into the vertebral body. The appropriate trajectory of the pedicle probe in the cranial-caudal direction is achieved by aiming toward the promontory.

Lateral x-rays are taken to confirm the tip of the probe end in the promontory of S1.

Cranial-caudal angulation of S1 pedicle screw

6. Screw insertion

Once the pedicle track has been created, it is important to confirm a complete intraosseous trajectory by pedicle and body palpation using a pedicle-sounding device. At any point in the process, radiographic confirmation can be obtained.

The selection of a mono- or a polyaxial screw is usually the surgeon's choice.


Confirming complete intraosseous trajectory prior to S1 pedicle screw insertion

A screw of appropriate diameter and length is carefully inserted into the trajectory.

Classically these screws are large in diameter but are shorter in length than the L5 screws. If screws are too long and breach the anterior cortex, the L5 nerve root and great vessels are at risk of injury.

An S1 pedicle screw of appropriate diameter and length is inserted
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