The pedicle screw is sometimes used in spinal fusion surgery to give an anchor point for connecting rods. The screws are placed at two or three places along the spine and then a short rod connects the screws. The rod and screws prevent motion at the spinal segments that are being fused.
The screws and rods are no longer needed for stability when the fusion is complete. The screws can be taken out but most surgeons don't advise this unless there is pain or discomfort.
Sometimes the screw breaks off and moves inside the body. In such cases, removal may be a good idea because there is a danger of damage to nearby blood vessels and nerves.
Doctors usually order imaging tests done to show the location of the loose screw. It may not need to be removed and removal would be an unnecessary surgery.