All of these variables have been worked out first in animal models. Then cadaver studies are done. Cadavers are humans preserved after death for study. When approved, scientists can begin limited studies on live humans. These are called clinical trials.
The Food and Drug Administration (FDA) must approve new devices such as the artificial disc replacement (ADR). Approval is required before they can be used in the general population.
At that point, small studies are often done with results reported at regular intervals months to years later. The hope is to attain positive results that last a lifetime.
In the case of ADRs, special motion X-rays can be taken to measure and quantify spinal motion. The imaging tool that can be used is called a roentgen stereometric analysis (RSA).
The patient lies on his or her back with the head in the middle. X-rays are taken to document the exact location of the ADR. The head is moved by the examiner to different points in the motion and new X-rays are taken.
Three-dimensional markers and computer analysis make it possible to keep track of each patient and compare results over time. Motion in flexion, extension, and rotations can be measured at each segment. This method is both precise and reliable.