Screw misplacement and screw loosening are two well-known complications of this type of surgery. The surgeon may not do anything just yet. It depends on the location of the screw. If the patient is not having any symptoms, there may not be any urgency in this situation.
However, if the screw is close to a major blood vessel or nerve pathway, it may be necessary to operate again and remove or replace the screw. Sometimes the surgeon opts to replace the screw(s) with hooks instead of screws. Hooks have their own set of potential problems so none of these tools are risk-free.
If the patient is experiencing pain and other symptoms, then the loose or misplaced screw(s) are revised or removed. The greatest concern is if the screw is close to the aorta, a major blood vessel carrying blood away from the heart. In a case like this, the screw will be removed even if there are no symptoms.