Do Intervertebral Discs Feel Pain?
Intervertebral discs are the cushions between the vertebral bodies, the bones that make up the spine. Normal discs move as universal joints in all directions allowing the free movements of the spine in daily activities. As discs age, they wear out and are less capable of cushioning the spine. Simple activities like walking can jar the spine and cause increasing pain. A question for doctors is whether the discs themselves are a cause of back pain.
The immediate answer would seem to be a resounding YES. However, what seems so obvious may not be backed by anatomic evidence. The intervertebral disc is mostly fibrous tissue and collagen. The disc consists of a jelly center, nucleus pulposus and the fibrous outer layer, the annulus fibrosis. Sensory nerves are generally absent from the disc except for the very outer layer. No nerve endings are actually present in the inner most portions of the disc. These anatomic facts are important to know in order to understand study results published in the Annals of Internal Medicine by doctors investigating the benefit of corticosteroid injections of intervertebral discs for chronic low back pain.
Doctors in France conducted a comparative clinical study to evaluate a single corticosteroid intradiscal injection for 135 chronic low back pain patients with acute discopathy. To participate in the study patients had to have chronic low back pain defined as daily pain for 3 months or longer and evidence of degenerative discs on magnetic resonance imaging. Half of participating received a fluroscopically-directed 1 ml contrast injection and half of the patients, an additional 1 ml of prednisolone acetate.
At 1 month after injection, 55% of individuals treated with the prednisolone injection experienced improvement in pain compared to 33% of those receiving no treatment. Eighty-four percent of individuals had improvement of back-related activities compared to 54% of untreated patients. However by 12 months, there was no difference in the improvement The benefits started to wane by 3 months after injection. No reversal of damage was demonstrated on repeat MR scans at 1 year in the injected intervertebral disc spaces.
This study raises the issue about the benefits of disc injection as a therapy, and the use of pressure injections in discs to identify painful vertebral levels. That issue is discussed in a separate post.
At best, corticosteroid injections of “discopathy” or inflamed, painful discs only have short-tern benefits limited to a month or two in chronic low back pain patients who have had pain duration measured in years. Better therapy may be exercise and nonsteroidal anti-inflammatory medicines that have benefits that are sustainable without additional damage to intervertebral discs.
David Borenstein, MD Executive Editor theSpineCommunity
Nguyen C, et al. Intradiscal glucocorticoid injection for patients with chronic low back pan associated with active discopathy: A randomized trial Ann Intern Med doi:10.7326/M16-1700
Carragee EJ,met al. A gold standard evaluation of the “discogenic pain” diagnosis as determined by discography. Spine 2006;31:2115-23