What is a disc herniation?
First, the disc itself needs to be addressed. A disc is the structure between the lumbar vertebral bodies (bones). The disc acts as a pad or cushion for the bone. The outer portion of the disc is made up of a tough fibro-cartilage matrix (the annulus) that is cross-linked in three different directions. In the middle, there is a gelatinous nucleus. (Some people describe the disc structure as resembling a jelly donut.) The disc allows for movement of the vertebral bodies and provides a buffer for compression between the bones. Normally, this system works very well.
Overhead diagram of a lumbar spinal disk
When a disc herniates, however, there has been a tear in the outer annulus, and the gelatinous center comes out through the tear. These herniations are described by their size, as follows: bulge (small), protrusion (slightly larger), extrusion (big) and a sequestered fragment (when some of the material has broken off from the disc). Once the disc has left its original anatomical position, the disc itself can be painful, it might irritate a nerve, or it may contribute to narrowing of the spinal canal.
(Brant-Zawadzki MN, Jensen MC, Obuchowski N, Ross JS, Modic MT: Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities. A comparison of two nomenclatures. Spine. 1995 Jun 1;20(11):1257-63; discussion 1264.)
There are two parts to this answer -- first, it is quite common to have disc herniations in the lumbar spine. In studies looking at people without back pain, a large percentage have had disc herniations that do not cause their back or leg to hurt.
Second, the term “disc herniations” is very broad. “Herniation” is a good – if broad – term to describe a change in the disc. In many ways, it is as generic as saying you drive “a car”. But that car can be a compact car, a sedan, a station wagon, or a large SUV. The same goes for disc herniations -- they can be disc bulges, protrusions, extrusions, or sequestered fragments. As they get bigger, they involve more symptoms.
(Boden SD, Davis DO, Dina TS, Patronas NJ, Wiesel SW: Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg Am. 1990 Mar;72(3):403-8.)
This is an excellent question, and there is a good answer. There are four reasons to seek a surgical solution:
(Weber H: The natural history of disc herniation and the influence of intervention. Spine. 1994 Oct 1;19(19):2234-8; discussion 2233. Review)
This question was answered in a very elegant study. Patients with different sized herniations (bulges, protrusions, extrusions) were assessed with a CT scan and then followed with MRIs. What they found was that by 6 months to 1 year, herniated disc material had dissolved in many of the cases. The larger the herniation (extrusions), the faster the material was reabsorbed.
Long term studies have shown that though surgical intervention might have a faster initial recovery time, conservative outcomes are as effective at 5 and 10 years.
(Saal JA, Saal JS, Herzog RJ: The natural history of lumbar intervertebral disc extrusions treated nonoperatively.Spine. 1990 Jul;15(7):683-6.)
(Birkmeyer NJ, Weinstein JN: Medical versus surgical treatment for low back pain: evidence and clinical practice. Eff Clin Pract. 1999 Sep-Oct;2(5):218-27)
(Weber H: The natural history of disc herniation and the influence of intervention.
Spine. 1994 Oct 1;19(19):2234-8; discussion 2233. Review)
The nerves that go to the legs come off of the spinal cord. As they come off, they run in the spinal canal and then come out between two of the vertebral bodies. When they are in the canal, they are named by the associated disc level (Lumbar 5 or L5). When the nerves come out the individual levels, they group together to make up named nerves, e.g., the sciatic nerve. It is in the canal that the disc irritates the nerve, sending pain down the leg corresponding to the disc involved and the side of the nerve that it irritates.
(Spencer DL: The anatomical basis of sciatica secondary to herniated lumbar disc: a review. Neurol Res. 1999;21 Suppl 1:S33-6. Review.)
(Ohnmeiss DD, Vanharanta H, Ekholm J:Degree of disc disruption and lower extremity pain. Spine. 1997 Jul 15;22(14):1600-5.)
There are a lot of options for non-surgical treatment of low back pain. The first is physical therapy. Good physical therapy will allow for the disc to heal and to provide improvements in biomechanics and strength. Recent studies have shown that directed physical therapy is more successful than more random approaches. Often, this is enough.
When the pain is too much to try physical therapy, however, epidural injections can also be very helpful. Epidural injections are safe when compared to more invasive procedures. Complications include bleeding, headaches, infections, and very rarely, injury to a nerve. However, pain reduction can be markedly improved. Studies have shown excellent pain reduction and return to function with the use of epidural injections.
The combination of these two techniques can be the most effective treatment of all -- the epidural provides pain reduction and makes the physical therapy that much more successful.
(Vad, Vijay B. MD ,*+++; Bhat, Atul L. MD ,[S]; Lutz, Gregory E. MD ,*+; Cammisa, Frank MD:Transforaminal Epidural Steroid Injections in Lumbosacral Radiculopathy: A Prospective Randomized Study. Spine. 27(1):11-15, January 1, 2002.)
(Weinstein SM, Herring SA: Lumbar Epidural Injections, Spine J. 2003 May-Jun;3(3 Suppl):37S-44S)
(Huston CW, Slipman CW, Garvin C: Complications and side effects of cervical and lumbosacral selective nerve root injections. Arch Phys Med Rehabil. 2005 Feb;86(2):277-83.)
(Lutz GE, Vad VB, Wisneski RJ: Fluoroscopic transforaminal lumbar epidural steroids: an outcome study. Arch Phys Med Rehabil. 1998 Nov;79(11):1362-6.)
(Fritz, Julie M. PhD, PT, ATC *; Delitto, Anthony PhD, PT, FAPTA *+; Erhard, Richard E. DC, PT: Comparison of Classification-Based Physical Therapy With Therapy Based on Clinical Practice Guidelines for Patients with Acute Low Back Pain: A Randomized Clinical Trial. Spine. 28(13):1363-1371, July 1, 2003.)