It is thought by some physicians that the clinical requirements of an ideal posterior motion preservation device include:
- A minimally invasive procedure
- Preservation or re-establishment of normal motion of the spine
- Avoidance of fatigue failure of the device
- Maintenance of normal resting posture of the spine without excessive kyphosis (upper spine curve) or lordosis (lower spine curve)
- Unloading of the disc, facet joints as well as the ligaments and muscles, and prevention of abnormal load distribution
- Easy salvage (ability to revise the procedure) in case of failure of the posterior stabilization device after surgery
The above requirements have been proposed by Dilip Sengupta, MD (note: Dr. Sengupta has designed a device that is in the process of being commercialized). Further research needs to be conducted in order to validate the above proposed requirements. Although there are multiple approaches for posterior motion preservation, the devices that address all the aforementioned criteria are primarily those that are known as the interspinous constructs. These devices are placed in the very back of the spine. They are not rigidly fixed to the spine and therefore are less subject to fatigue associated with long term motion.
There are several pedicle screw based dynamic stabilization devices. One attractive feature of these devices is that many spine surgeons are already very familiar with the technique of pedicle screw placement. Rather than attaching a rigid rod to the screws, as was originally done when using the implant to facilitate immobilizing the spine (for a spinal fusion), flexible devices are attached instead.
It should be emphasized that none of the devices in this category of spine surgery have withstood the test of time, and most are still in various stages of investigation. For example, there is some concern that interspinous devices may lead to kyphosis, but to date there is no data to suggest that kyphosis develops and this will only be proven or disproven over time.