Dr. Corenman Discusses the
Lower back pain is typically caused by a degenerative disc. As noted in the discussion of the anatomy and physiology of the disc (how the disc is designed on the microscopic level) on this web site, the disc develops degenerative changes as the nucleus (the jelly in the center of the disc) loses pressure and the wall of the disc (the annulus) buckles and tears.
The back of the disc wall is filled with pain receptors and they send pain signals to the brain when this wall is torn. Most of the time, these signals are mild to moderate in intensity. Physical therapy, core strengthening, certain activity restriction and medications including non-steroidal anti-inflammatories can mute these signals. These modalities and restriction reduce the intensity of the pain and make life “livable”.
The disc can continue to degenerate and develop “micro instability.” This causes abnormal forces to occur and chronically overloads the rings of the annulus. Multiple tears in these rings allow the disc to lose height and integrity. The inner jelly (nucleus) dries up further causing a greater drop in height. At this stage, the back can “go out” with certain activities. If these activities are avoided, the individual can live a guarded but acceptable life using the therapy noted above.
The disc can continue to degenerate and lose the ability to act as a shock absorber. The cartilage of the endplates erodes away. Damage to the bony endplates of the vertebra occurs as the bone endplate is overloaded with impact activity. Fractures of the endplate occur in a condition called isolated disc resorption or IDR.
Endplate healing can occur but the cause of the fracture (the loss of shock absorption) will still be present. Any activity in the next sixty days while the fracture is healing will disrupt the repair. Of course, no one is going to be placed in a body cast and lie perfectly flat while the fractures are in the state of repair. Also, the initial cause of the fracture (lack of shock absorption) is still continuously present. Any impact activity will cause further injury to the endplates.
You can see how the endplates of the vertebra would be in a continuous state of repair and disruption with any activity- even the act of stepping off a curb. This causes chronic inflammation, which is a setup for chronic pain. Not everyone with this exact condition has severe chronic lower back pain and some with this disorder may even not even notice pain. The answer why some will and some will not have pain will be a Nobel Prize winning answer.
It should be noted that not every disc will follow this degenerative pattern and it is not inevitable that all discs will continue down this pathway. Even though the damage to the disc is permanent (there is no blood supply to heal the disc), most discs do not suffer the endpoint fate of IDR.
An important aspect of isolated disc disruption is that even though the condition is significantly painful, it is not dangerous (as long as there is no concordant significant compression of the nerves in the spinal canal- a different story). Isolated disc disruption will not put the individual in a wheelchair or cause paralysis. The pain is similar to an arthritic hip or knee in that use of the degenerative area is painful.
Of course, even though this pain is not dangerous, it is debilitating. If the pain is intolerable, the removal of the overloading forces and the repair of the vertebral integrity is essential to reduce the pain. Bone is designed to transmit force without injury to itself. The purpose of fusion in the lumbar spine is to make a living bridge of bone from one vertebra to the next. This is a wonderful way to transmit force to the next vertebra by inducing a fusion of living bone and eliminate what is left of the motion that causes the pain.
Now an argument is made that taking away motion of a segment will put stress on the next level above or below. The obvious counterargument is that the degenerative forces have already made this level relatively immobile. You have to remember that this highly degenerative level is already quite stiff and relatively fixed.
Generally the normal L5-S1 level has about 25 degrees of motion. With the presence of IDR, the remaining motion in this level typically is about 1-2 degrees. You can see that living with this degenerative disc will not change the already stressed the level above. Providing a fusion generally eliminates the lower back pain without any additional stress to the surrounding levels.
Issues with Artificial Disc Replacement (ADR)
The concept of the artificial disc replacement (ADR) was born to try to preserve or improve spine motion. The idea itself has merit but the current implants are not satisfactory. The design of the artificial disc is not at this point a good reproduction of the normal disc that it is designed to replace.
The current lumbar ADRs do not have any shock absorption capabilities and do not dampen motion of the disc space as a normal disc would. The ADR’s lack of these normal discal characteristics puts more stress on the replaced segment than it was designed to tolerate. In addition, if there was substantial wear of the original disc space before surgical replacement, the artificial disc will still not relieve the lower back pain if there is damage to the other structures such as the facets.
Another important fact to consider in a much worn out disc level such as with IDR is that the body had adapted for years to the loss disc height and of motion. Implanting an artificial disc in a very worn out segment will increase motion and increase the height of the disc. All the associated structures that have adapted to the vertebral collapse and stiffness will become stretched and dysfunctional, increasing back pain in spite of an ADR.
After placement of an ADR and aging, the vertebral bone can becomes osteoporotic (especially in females) and the artificial disc metal endplate can fracture the endplate of the vertebra. This will cause the ADR to subside into the bone. The biomechanics of the disc are lost with malalignment and pain ensues.
Another problem is that these discs have to be placed from the front through an incision through the belly, which has its own potential complications. See ALIF-anterior lumbar Interbody fusion for an understanding of the potential complications of an anterior approach.
This is why the current gold standard for treatment is a fusion for lower back pain. The procedure works in over 90% of correctly selected patients.
Fusion for Lower Back Pain Types
Fusions for lower back pain can be performed in various ways. Fusion can be performed from various approaches:
Each fusion has its own indications, risks and benefits. See the discussion of each fusion in the surgical section.
To discuss the indications for fusions for lower back pain in greater detail, please contact the office of Dr. Donald Corenman, spine surgeon and back pain specialist serving the communities of Vail, Aspen, Denver and Grand Junction, Colorado.