For patients researching different treatment alternatives for spine pain, it is always important to remember that no one device or class of devices offers a cure all: the key to providing lower back pain relief is to identify the cause of the patient’s symptoms as specifically and comprehensively as possible. The ability to isolate the actual cause of the pain for the patient determines which device and procedure should best address the structural problem(s) causing the patient’s pain.
For patients with ongoing pain originating from the spine, the classic surgical treatment has usually been spinal fusion. Similar to degenerative painful conditions of the hip and knee, degenerative, painful spine surgical treatment is now evolving from fusion, which eliminates motion at the joint, to the goal of motion preservation. There are several alternative approaches to motion preservation, some of which have been approved for use in the general patient population in the US and many of which are in various stages of development and clinical trials:
Total disc replacement. The initial approach for motion preservation in the USA has involved total disc replacement to address painful disc degeneration. There are two artificial discs currently available in the U.S.: the CHARITE lumbar artificial disc, which received FDA approval in October 2004 and the PRODISC-L lumbar artificial disc, which received FDA approval in August 2006. Other total disc replacements will likely soon receive approval and be available to patients as well.
Disc nucleus replacement. Also in development are nucleus replacement devices, which seek to address discogenic pain by replacing only the disc nucleus (the center of the disc) while leaving the outer portion (the annulus) of the disc intact.
While representing a breakthrough in treatment for many patients with ongoing back pain, disc replacement cannot be expected to address pain in all patients with low back pain, as the source of the patient’s pain is not always a painful disc or well defined. For example, total disc replacement does not address pain originating from the posterior elements (in the back of the spine), such as pain that originates from the facet joints, ligaments, tendons, or muscles. Posterior conditions (problems in the back of the spine), such as spinal stenosis, may be improved with posterior motion preservation devices. These devices can be put into three general categories:
Interspinous process spacers. These devices are designed to distract (open) the central canal and foramen, where the nerve endings pass away from the center of the spinal region and into the legs. These devices are designed to address pain and activity restrictions from spinal stenosis, and some may be used to treat degenerative disc disease.
Posterior dynamic stabilization devices. Analogous to an internal brace on the spine, the goal of posterior dynamic stabilization devices is to allow controlled motion in such as way as to achieve more normal movement of the spine. These devices are typically used to treat patients with spondylolisthesis and degenerative disc disease and to date have been approved for use with fusion, but not for independent use as dynamic stabilizers. Clinical trials are currently underway for some of these devices for use as stand-alone devices (without fusion), and for use in the treatment of lumbar spinal stenosis.
Facet replacement or total element replacement devices for spinal stenosis. These devices are primarily designed to address pain due to facet pain or lumbar spinal stenosis (narrowing of the passageways of the nerves). For many patients, spinal stenosis is due to degeneration of the facet joints. Facet replacement devices replace the facet joints in the back of the spine to limit or control motion, and total element replacement devices replace all the elements in the back of the spine.
In lumbar spinal stenosis, the cauda equina or spinal nerve roots in the low back are compressed, producing pain, tingling, weakness or numbness that radiates into the buttocks and legs. In most cases, walking will produce pain into the legs, and the pain will be relieved when sitting. The decision to have surgery for spinal stenosis is usually made by patients who have been unresponsive to non-surgical treatments and no longer want to live with activity restrictions.
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 are no data to suggest that kyphosis develops and this will only be proven or disproven over time.
This article discusses the following categories of posterior motion preservation devices:
