A bone screw is a metal implant inserted into the bone. Screws are used to immobilize fractured bone segments to aid in the healing process, and as an adjunct to spine fusion surgery to help hold implants in place.
An example of a bone screw commonly used in spine fusion surgery is called a pedicle screw, which holds rods into the spine. The screws are placed at two (or sometimes three) consecutive spine segments (e.g. lumbar segment 4 and 5) and then a short rod is used to connect the screws.
The design of the screws and rods helps prevent motion at the spinal segments that are being fused, thus aiding in the bone healing process of the fusion. After the bone graft grows and a fusion has taken place, the screws and rods are no longer needed for stability but are usually left in place.