Bone screws have been used in spinal instrumentation since the 1960s. A pedicle screw is a particular type of bone screw designed for implantation into a vertebral pedicle.

 

What is the vertebral pedicle?
The pedicle is a dense stem-like structure that projects from the posterior of a vertebra. There are two pedicles per vertebra that connect to other structures (e.g. lamina, vertebral arch). The location of a pedicle is illustrated below.

 

Polyaxial Pedicle Screws
Today's standard is a polyaxial pedicle screw made of Titanium, which is highly resistant to corrosion and fatigue, and is MRI compatible. The screw is threaded and the head is mobile - it swivels helping to defray vertebral stress. Like other screws, polyaxial screws come in many sizes. Polyaxial pedicle screw length ranges from 30mm to 60mm (up to 2-1/2 inches). The diameter ranges from 5.0mm to 8.5mm (up to 1/4 inch).

Purpose
These screws are used to correct deformity, and/or treat trauma. Similar to other bone screws, pedicle screws may be used in instrumentation procedures to affix rods and plates to the spine. The screws may also be used to immobilize part of the spine to assist fusion by holding bony structures together.

Placement
Although pedicle screws are most often used in the lumbar (lumbosacral) spine, they can be implanted in the thoracic and sacral vertebra. The surgeon uses fluoroscopy or conventional x-ray to determine the depth and angle for screw placement. A receiving channel is drilled and the screw is inserted.