The spine consists of a column of bones called vertebrae, which enclose and protect the spinal cord and its branches (nerve roots). Vertebrae are separated from each another by intervertebral discs - circular pads that provide cushioning, shock absorption, and spinal flexibility. These discs are composed of a soft gel-like center (nucleus pulposus) surrounded by a tough outer ring of fibrous cartilage (annulus fibrosus).
A herniated disc develops when the soft nucleus pulposus bulges out into the spinal canal. This protrusion, commonly known as a slipped disc or ruptured disc, is a problem because it can compress and irritate a nearby spinal nerve root.
Frequently, herniated discs occur in middle-aged people following strenuous activity, but in many cases there is no precipitating event. The most common location for a herniated disc is the low back (lumbar spine). This disorder sometimes affects the neck (cervical spine) but rarely affects the middle back (thoracic spine).
Causes and Risk Factors
As adults age, the discs tend to deteriorate in a process called disc degeneration that narrows the spaces between vertebrae and increases the likelihood of disc herniation.
Herniated discs are associated with certain risk factors:
- Back or neck injury
- Lifting objects improperly
Most lumbar disc herniations develop between the 4th and 5th lumbar vertebrae or between the 5th lumbar vertebra and the sacrum. Cervical disc herniations most likely occur between the 5th and 6th cervical vertebrae or between the 6th and 7th cervical vertebrae.
Herniated discs usually elicit symptoms on one side of the body as the protruding disc presses on the spinal nerve roots at the corresponding level of the spine. The resulting nerve root irritation (radiculopathy) manifests as pain, numbness, and weakness in the extremity supplied by the affected nerve.
Symptoms of a lumbar herniated disc include:
- Low back pain.
- Shooting pain from the buttocks to the leg (termed sciatica because the pain travels down the sciatic nerve).
- Tingling and numbness in the buttock or leg (paresthesias).
- Weakness in one or both legs.
- Loss of bowel or bladder control (occurs when a large disc protrusion injures the cauda equina, a group of nerve roots resembling a horse’s tail, at the bottom of the spinal canal). This emergency, called cauda equina syndrome, must be immediately treated with surgery.
Symptoms of a cervical herniated disc include:
- Pain in neck.
- Pain in the shoulders.
- Pain that shoots down the arm.
- Tingling and numbness in the shoulder or arm.
- Weakness in one or both arms.
- Rarely, numbness and weakness in the legs (from pressure on the spinal cord).
Diagnosis and Treatment
A physical examination may reveal decreased feeling, weakness, or diminished deep tendon reflexes in the area of the extremity served by the affected nerve root.
For lumbar herniated discs, a positive straight leg raising test confirms nerve root compression when a patient experiences pain down the back of the leg upon lifting the leg with a straight knee.
- X-rays of the spine may show degeneration of disc spaces but cannot show details about the discs themselves.
- Computed tomography (CT) provides much more detailed images of the spinal structures.
- Magnetic resonance (MRI) uses radio waves and a powerful magnet to create additional images of the spinal structures and surrounding tissues.
- Myelogram involves injecting dye in the spinal fluid followed by X-rays to take pictures of the spinal canal.
- Electromyography evaluates the function of nerves and muscles.
- Nerve conduction studies test how well the electrical signals travel in the nerves.
Overall, 90% of patients are effectively managed with nonsurgical treatments:
- Anti-inflammatory medications, such as ibuprofen, decrease swelling and pain.
- Muscle relaxants, such as cyclobenzaprine, relieve muscle spasms. Side effects may include drowsiness.
- Medications for nerve injury (neuropathic pain) include pregabalin, gabapentin, and duloxetine. Side effects include dizziness, fatigue, and drowsiness.
- Narcotics, for severe pain, include oxycodone and hydrocodone. Side effects include sedation, nausea, and constipation.
- Epidural steroid medication (injected into the space just outside of the sac of spinal fluid), reduces swelling, inflammation, and pain.
- Physical therapy and back-strengthening exercises are more effective treatments than bed rest.
- A soft cervical collar may help alleviate neck pain.
Most cases resolve with nonsurgical treatment; however, after 6 weeks, surgery is indicated for patients experiencing persistent pain, progressive weakness, or difficulty walking. Emergencies, like cauda equina syndrome, require immediate surgery to prevent permanent nerve injury and loss of function.
Microdiscectomy is the most common procedure for lumbar herniated disc. In this surgery, a microscope allows the surgeon to view the structures and remove the protruding portion of the disc through a small incision.
In the neck, an anterior cervical fusion is performed with an incision on the front of the neck. Most of the disc is removed and replaced with a piece of bone graft that joins two vertebrae together and stabilizes the neck.
Techniques for proper lifting, sitting, standing, and posture may prevent herniated discs. When lifting heavy objects, people should use their leg muscles instead of their backs and avoid twisting while lifting.
The results of regular exercise - normal body weight, strong muscles, increased flexibility - promote a healthy spine and decrease the risk of herniated discs.
Chad DA. Ch 75. Disorders of Nerve Roots and Plexuses. In: Daroff R, Fenichel GM, Jankovic J, Mazziotta J, eds. Bradley’s Neurology in Clinical Practice. 6th ed. Philadelphia, PA: Elsevier Saunders: 2012.
Herniated Disk. American Academy of Orthopaedic Surgeons website. http://orthoinfo.aaos.org/topic.cfm?topic=a00334. Accessed April 21, 2014.
Herniated disk. PubMed Health, U.S. National Library of Medicine, website. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001478/. Accessed April 21, 2014.
Herniated Disk. Mayo Clinic website. http://www.mayoclinic.org/diseases-conditions/herniated-disk/basics/definition/con-20029957. Accessed April 21, 2014