A procedure and system for determining and placing spinal implants or prostheses includes measuring a change in position of vertebrae at an affected level of a patient's spine from a first position where the patient reports greatest pain at the affected level, to a second position where the patient reports least pain at the affected level. Spinal implants or prostheses are selected so as to urge the affected level of the spine toward the second position and away from the first position when the implants are placed at the affected level. In one embodiment, an implant device is formed by one or more inflatable balloons that are placed at determined locations inside a disc space at the affected level. When the balloons are inflated, vertebrae above and below the balloons are urged toward the second position and away from the first position at the affected level.