Devices in this category can best be described as an internal brace - allowing controlled movement of the affected segment of the spine. Most of these devices tend to be derived from the pedicle screw and rod constructs (used in spinal fusion surgery) of the 1980s and 1990s. Those devices were designed to provide rigid stability to the spine while boney incorporation of the fusion mass was achieved. The goal of the new generation of devices is to allow controlled motion in such as way as to achieve more normal movement of the spine.
Several of these devices have been approved for use as an adjunct to spinal fusion, and are now being tested as a standalone device.