What causes a herniated disc?
The discs of the spine are located between the vertebrae (bony building blocks of the spine). The disc is designed somewhat like a jelly donut being composed of an inner gelatin-like core (the nucleus pulposus) surrounded by a firm outer ring (the annulus fibrosus).
When the disc structure wears, because of processes such as aging or trauma, it becomes weakened and susceptible to injury. In this condition, stresses on the spine can cause the inner core to protrude outward through the boundary of the disc's outer ring. The is referred to as herniation of the disc.
Disc herniation can directly press upon the spinal cord and/or adjacent nerve tissues resulting in pain which radiates outward from the spine in the distribution of the affected nerve. When the disc herniation is in the spine of the lower back, it can cause a radiating pain down the legs, commonly referred to as sciatica.
A majority of patients with sciatica from disc herniation have resolution of their pain with various conservative measures, including anti-inflammatory and muscle-relaxant medications, exercises, physical therapy, and time. However, some 10%-15% of affected patients require surgical procedures to relieve the pain.
Success rates of cortisone injections for back pain
In recent decades, cortisone medications have been injected into the space around the spinal cord (epidural space) to reduce the inflammation and swelling of the disc herniation, thereby relieving irritation of the adjacent nerves. It has never been certain as to whether this procedure (epidural injection) can actually reduce the need for surgery.
A study by Simon Carette, MD, and others from Laval University and the University of Montreal, looking at the long-term benefits of epidural injection for sciatica from disc herniation, was published in the New England Journal of Medicine (1997;336:1634-40).
Dr. Carette's study found that although epidural injections for disc herniation of the low back relieved pain in the leg temporarily, the benefit was short-lived. In fact, after three months, there was no benefit from epidural injection compared to saltwater placebo injection. Further, the need for surgery was not influenced by the injection even one year later.
Dr. Carette's study demonstrated that epidural cortisone injections can relieve pain in the short-term. However, this study seems to suggest that undergoing an epidural cortisone injection for sciatica from a herniated disc in order to avoid surgery may not be valid.
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Jacobs, W. et al. "Surgery versus conservative management of sciatica due to a lumbar herniated disc: a systematic review." Eur Spine J. Apr 2011; 20(4): 513–522.