Using metal plates and screws to help stabilize the spine is called spinal instrumentation. Rigid fixation of the spine through this type of fusion is often needed after trauma. Degenerative disease and tumors can also result in spinal instability requiring this type of fixation.
The placement of the screws varies depending on the problem. Inserting the screws into the pedicles is a common way to stabilize the vertebrae. The pedicles are part of the vertebral segment where the bony ring attaches to the main body of the vertebra.
Perforations of the screw can occur when the size of the screw is larger than the diameter of the bone. Problems can occur if the screw pushes into a blood vessel, nerve, or the spinal cord.
But surgeons often use a technique called the in-and-out to avoid this problem. The screw is threaded in and out of the bone to avoid hitting the wall of the pedicle. The threads of the screw might be exposed but there’s no danger to the nerves or vessels.