Sciatica

05 August 2010

Overview

Sciatica is a condition of pain that is found along the distribution of the sciatic nerve, and is secondary to pathology of the nerve itself (1).  The sciatic nerve is derived from the lumbar and sacral spinal nerves L3 to S3, and receives fibers from both the anterior and posterior divisions of the lumbosacral plexus.  Beginning in the spine the nerve runs through the buttocks, down the back of the leg, behind the knee, and branches before reaching the foot.  This nerve controls the muscles of the back of the knee and lower leg and provides sensation to the back of the thigh, part of the lower leg, and the sole of the foot.  Of interest, the sciatic nerve is the largest nerve in the human body, nearly the same diameter of a finger.  Sciatica is usually felt as pain radiating from the buttocks down the back of the thigh into the calf and foot.   The pain, which can be sharp, shooting, burning, or shock-like, is typically uniform along the nerve, but may present as "hot spots" of worsened pain along the length of the nerve.  Sitting, standing up, walking, coughing, sneezing, or other sudden movements can worsen the pain.  The term "sciatica" is commonly used incorrectly to describe all pain radiating into the leg.  However, there are other structures in the spine and pelvis that can be responsible for referred pain to the buttock and leg, such as the sacroiliac joints, facet joints, and intervertebral discs.  Associated numbness and/or tingling indicates a neuropathic source of pain like sciatica and helps to differentiate it from "other" causes.

Fortunately, most patients with sciatica respond to conservative management and the symptoms tend to self-resolve in a matter of weeks to months. Conservative treatment encompasses alternating cold packs and hot packs, stretching, exercise, and use of over-the-counter (OTC) medications.  A study of 214 patients with an acute onset of sciatica were treated with 1 week of bed rest, followed by gradual use and OTCs, experienced that pain significantly dropped within 4 weeks (2).  Although short-term bed rest is recommended during the acute phase, activity that does not cause severe pain may actually be good.

Even though the majority of sciatica pain is self-limiting, when present in the following situations an individual should seek medical attention:

• Fever or temperature over 100⁰ F
• IV drug use, which increases risk of an infectious cause.
• Neck Pain worse at rest, which may be associated with an infectious cause or cancer.
• Unexplained weight loss, which may be associated with cancer.

When the following conditions are present one should seek emergent care:

• New or unexplained weakness or paralysis
• Loss of Bowel or Bladder Control
• Recent significant trauma such as a fall from a height or motor vehicle accident

Sciatica Video

This episode of The Pain Show explains Sciatica pain and treatment options including Epidural Steroid Injections. This episode also includes pain news explaining “deskercise,” a new way to keep healthy while you work! Arizona Pain Specialists also treats a variety of pain conditions including back pain, neck pain, facial pain, knee pain, and many more.

Statistics: Incidence/prevalence

Sciatica is relatively common affecting 15% to 40% people during their lifetime.  The incidence of sciatica is between 1% to 5% annually (3,4).  This incidence is related to age, with any occurrence before 20 years old being extremely rare.  The highest incidence is found in the fifth decade and then decreases with increasing age (3).

There is an interesting relationship between physical activity and sciatica.  While regular joggers without a history of sciatica have a decreased incidence of sciatica, those who had a previous history of sciatica experienced more episodes (5).  Regular walking also was found to increase the incidence of sciatica by nearly two-fold.  In addition, occupations with greater physical labor, such as carpenters and machine operators, have a higher likelihood of developing sciatica compared to less mobile office workers (6,7).

Pathophysiology

In the 1930s intervertebral disc protrusion and subsequent pressure on the sciatic nerve roots were thought to be the likely source of sciatica (8).  The cure for this condition would logically be surgical removal of the disc to relieve the pressure on the nerve.  Twenty years later publications presented arguments that pressure on nerves leads to loss of function and rarely to pain 59.  Multiple studies have shown that patients are frequently asymptomatic despite having significant disc pathology (9,10).  Furthermore, patients that have symptomatic disc herniation may not experience relief from removal of disc material or other causes of compression, while others experience significant relief in the absence of any intervention (11).  Although the pathophysiology is still not clearly understood, there is evidence to suggest that the nucleus pulposus triggers an inflammatory response in sciatic nerve roots and may lead to pain.   Contrary to previous theories, multiple factors including inflammation, abnormal immune factors, and mechanical compression of the nerve are likely involved in producing pain.

Causes of Pain

Spinal disc herniation

Each vertebrae is separated by an intervertebral disc, which is a soft cushion that provides support and absorbs the stress that the vertebrae receive during daily activities. The disc consists of an inner, gel-like substance called the nucleus pulposus, and an outer fibrous membrane called the annulus fibrosus.  A herniated intervertebral disc results from the weakening and bulging outwards of the annulus, and protrusion of the nucleus, which most commonly occurs posteriorly or backwards. The spinal disc is in close vicinity to the nerve roots as they branch from the spinal cord and exit between the vertebrae. Therefore, a disc protrusion in the lumbar spine may compress one or more nerve roots causing pain to radiate into the back or legs.  As mentioned above, the nucleus polposus may cause inflammation of surrounding tissue which may cause further compression of the nerve root.

Spinal stenosis

Narrowing of the spinal canal usually caused by a herniated disc, thickening of ligaments, overgrowth of the facet joints, spondylosis, tumor, or infection. The primary symptoms are chronic pain and numbness, but may result in lower extremity weakness and gait disturbance. The most serious complication is myelopathy, which occurs after damage to the spinal cord.

Spondylolisthesis

Often results from a stress fracture at the L5 vertebra.  When the fracture is combined with disc space collapse the vertebra may slid over the underlying vertebra causing the nerve root exiting at this level to become pinched.

Piriformis syndrome (PS)

In about 1 in 10 people the sciatic nerve runs through a small muscle in the buttocks called the piriformis muscle instead of the usual path underneath it.  When the muscle contracts or spasms  it can compress the sciatic nerve inside the muscle leading to sciatica. It is also referred to as the "wallet sciatica" since a wallet carried in a rear hip pocket will compress the muscles of the buttocks and sciatic nerve when sitting down.  Treatment for PS has historically focused on physical therapy modalities, with refractory patients also receiving local anesthetic and corticosteroid injections.

Pregnancy

The sciatic nerve courses under the uterus on its way to the leg.  As the uterus grows during pregnancy it places increasing pressure on the sciatic nerve, which may cause pain.  Muscular tension and vertebral compression secondary to increased weight may also contribute to sciatica during pregnancy.  The simplest solution may be to lie on the side opposite of the pain in attempt to relieve the pressure of the uterus.

Other causes:

• Malignancy: Metastatic bone or soft tissue sarcoma, sciatic neuroma, haemangioblastoma
• Infection: Abscess, caseating disease, discitis
• Vascular compression: Abnormal pelvic venous plexi, gluteal artery pseudoaneurysm
• Compression: Epidural adhesions
• Gynaecological: Uterine fibroid, pelvic endometriosis (cyclic pain)

Risk Factors:

• Positive influence
• Increasing height (older age groups only)
• Age
• Genetic pre-disposition
• Walking
• Jogging (pre-disposes to pain if previous history exists)
• Occupation (particularly if associated with physical activity, especially flexion/torsion of trunk, arms frequently raised above shoulder height, driving of motor vehicles)
• Smoking
• No influence
• Gender, body mass, parity
• Negative influence
• Jogging (if no baseline history of sciatica) 12)

Diagnosis

Physical Exam findings test

A physician will perform an exam by observing the patient's general gait and posture.  In addition the physician will palpate or feel the spine, surrounding tissue, and joints.  Finally, neurologic signs including range of motion, muscle strength, reflexes, sensory signs and straight leg test are assessed.

Imaging

Together with a thorough history and examination, imaging studies may prove to be critical in formulating a differential diagnosis and identifying the correct pain generator.  Imaging modalities that may be useful in diagnosing sciatica include cervical radiographs (x-ray), computed tomography (CT scans), and magnetic resonance imaging (MRI).  X-rays should not be obtained until four weeks of conservative treatment have failed, unless the patient presents with trauma, symptoms of infection/cancer, or worsening neurologic deficits.  MRI is indicated for progressive neurologic loss, disabling weakness. CT myelography should not be used as the initial test unless MRI is contraindicated, as MRI is better for seeing spinal cord lesions and pathology.

Neurophysiologic procedures are needed when the exam and imaging studies do not match.  Electromyography, nerve conduction studies, and somatosensory evoked responses help to decipher between spine and peripheral problems as well as nerve root problems from a radiculopathy.

Diagnostic Interventions

• Selective Nerve Root Blocks are a local injection procedure used for diagnostic and therapeutic purposes.  It has also been used when the clinical exam and imaging studies fail to correlate.
• Discography is used to determine whether or not pain is coming from a disc and for identifying abnormalities in the disc.
• Abnormalities can include disc herniations, tears and fissures.  This procedure involves the injection of contrast dye into the center of a disc under x-ray guidance. It is strictly a diagnostic procedure.

Treatment

Medical Treatment Options

Medications by Class

• Non Steroidal Anti-Inflammatory Drugs (NSAIDs): Ibuprofen, Advil ®, Aleve®, Nuprin®, Motrin® and others are anti-inflammatory medications.  These medications provide good short-term relief of neck pain and can be used as an adjunct for long-term pain conditions. Because of the risk of ulcers, gastrointestinal bleeding, and decreased kidney function talk with your doctor before using these medications.
• Acetaminophen (Tylenol®): has been shown to be as effective as ibuprofen in relieving pain.   This medication is often added to other pain medications because of its synergistic effect with these medications.  This medication must be taken as directed and care should be taken when taken regularly, as excessive use can cause liver dysfunction.
• Muscle relaxants: including cyclobenzaprine (Flexeril), metaxalone (Skelaxin®), methocarbamol (Robaxin), tizanadine (Zanaflex), baclofen (Lioresal), and carisoprodol (Soma) treat painful muscle spasms.  The most common side-effects include drowsiness, dizziness, drug interactions, and abuse (most commonly with Soma).
• Anti-Convulsants: are also considered membrane stabilizing medications as they are believed to “calm down irritated or hyperexcited nerves” which are responsible for neuropathic pain.  These medications include gabapentin (Neurontin), pregabalin (Lyrica®), topiramate (Topamax), and others.  Many have the side-effect of weight gain (excluding topiramate), drowsiness, dizziness, and trouble concentrating.
• Anti-Depressants: are also considered membrane stabilizing medications as they are believed to “calm down irritated or hyperexcited nerves” which are responsible for neuropathic pain.  Within these medications are multiple tricyclic anti-depressant (TCAs) medications, which include the commonly used pain medications amitryptiline (Elavil) and nortriptyline (Pamelor).  Newer anti-depressant pain medications are in the serotonin norepinephrine reuptake inhibitor(SNRI) category.  These medications include duloxetine (Cymbalta®) and milnacipran (Savella®).
• Steroid medications: A high-dose, fast-taper course of corticosteroids (ie. Medrol dose pack) can be used if there is a strong suspicion of nerve root impingement by disk protrusion or spondylosis.
• Opioid medications: are also called narcotic pain relievers.  These include codeine, hydrocodone, morphine, oxycodone, oxymorphone, hydromorphone, meperidine, fentanyl, methadone, propoxyphene and other medications.  These medications are used to treat severe pain.  Side-effects commonly include nausea, drowsiness, dizziness, tolerance, constipation, and addiction.

Minimally Invasive Options

• Epidural Steroid Injections (ESIs). The procedure involves injecting a corticosteroid under x-ray guidance into the epidural space, which is the space around the spinal cord.  The steroids act on the nerve roots as they branch from the spinal cord by decreasing the swelling and nerve root impingement.  A meta-analysis looking at 11 studies of ESIs found a greater than 75% improvement  in pain relief for up to 60 days in patients suffering from sciatica (13).
• Lysis of Adhesions (adhesiolysis) is also known as the "Racz procedure" because it was invented by Dr. Gabor Racz.  The procedure is similar to an epidural steroid injection, but is designed to dissolve scar tissue in the epidural space.  It is used to treat post-laminectomy syndrome, radiculopathy, spinal stenosis, and disc disease.
• Spinal Cord Stimulator (SCS), known as the “pacemaker for pain” is a minimally invasive procedure that involves implanting a device that applies low currents of electrical stimulation through thin wires.  The leads or wires are placed under x-ray guidance into the epidural space, where they block pain signals.
• Botox Injections The procedure involves an injection of a small dose of botulinum toxin into spastic muscles.  Botulinum toxin (botox) has recently been used to treat PS and is gaining popularity (14).

Surgical Interventions

Typically, surgeons use two surgical techniques for sciatica:

• Spinal Decompression in which pressure on the spinal cord or spinal nerve roots is reduced by:
  • Discectomy - Removing part or all of an intervertebral disc
  • Laminectomy - Removing part of the spinal bone
  • Foraminotomy - Removing bone and/or disc that encroach upon a nerve foramen
• Spinal Stabilization in which the surgery limits motion between vertebrae:
  • Disc Replacement - artificial cervical disc replacement involves implanting a disc after a discectomy is performed.
  • Spinal Fusion - involves joining selected bones in the neck together using a bone graft, screws, rods and plates.

Complementary and Alternative Treatment Options

• Physical Therapy is beneficial in both rehabilitation from an injury and prevention of future injury. Passive physical therapy involves: heat/ice packs, TENS, ultrasound.  Active physical therapy includes: stretching, strengthening exercises, spinal manipulation, and low-impact aerobic conditioning.
• Chiropractic Manipulations that are done correctly as targeted adjustments may significantly reduce neck pain when combined with other modalities of treatment.
• Exercise works similar to physical therapy by increasing strength, and also releases endorphins.
• Proper nutrition can prevent nutritional deficits, which may otherwise lead to accelerated degenerative disease. A diet rich in Omega-3 fatty acids has been recommended for many purposes, but pain relief hasn’t been one of those until recently. Research has suggested that omega-3 is an “attractive adjunctive treatment for joint pain associated with rheumatoid arthritis, inflammatory bowel disease, and dysmenorrhea” (15).  A great way to increase omega-3 consumption is to add ground flax seed to daily meals.
• Acupuncture involves placing small needles into the skin, causing release of hormones called “endorphins“, the body’s natural pain reliever.  Acupuncture has been used for several thousand years to treat pain and other maladies and has been shown to be very helpful at relieving symptoms in those with chronic pain.
• Biofeedback is a treatment that teaches a patient to become aware of his/her body processes that are normally thought to be involuntary, such as temperature regulation, heart rate, and muscle tension.  A better awareness of one’s body teaches one to effectively relax and can help to relieve pain.
• Transcutaneous Electrical Nerve Stimulation (TENS) is a technique that relieves pain by applying mild electric current to the skin at the site of the pain.
• Massage of the tender areas may help relieve muscle spasms or contractions and provide pain relief.
• Yoga is a program of exercises to help improve flexibility.  Yoga leads to a decrease in stress and maintains health. The basic components of yoga are proper breathing, stretching, and posture.

References

1)  Merskey H, Bokduk N. Classification of Chronic Pain (1994) 2nd Edn. IASP Press. 13,–15, 198.

2)  Weber H, Holme I, Amlie E. The natural course of acute sciatica with nerve root symptoms in a double-blind placebo-controlled trial evaluating the effect of piroxicam. Spine (1993) 18:1433–8.

3)  Frymoyer J. Lumbar disc disease: epidemiology. Instr Course Lect (1992) 41:217–23.

4) Frymoyer JW. Back pain and sciatica. N Engl J Med (1988) 318:291–300.

5)  Miranda H, Viikari-Juntura E, Martikainen R, Takala EP, Riihimaki H. Individual factors, occupational loading and physical exercise as predictors of sciatica pain. Spine (2002) 27:1002–9.

6)  Riihimaki H, Tola S, Videman T, Hanninen K. Low back pain and occupation. Spine (1989) 14:204–9.

7)  Riihimaki H, Viikari-Juntura E, Moneta G, Kuha J, Videman T, Tola S. Incidence of sciatic pain among men in machine operating, dynamic physical work and sedentary work. Spine (1994) 19:138–42

8)  Mixter WJ, Barr JS. Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med (1934) 211:210–5.

9)  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) 72:403–8.

10)  Boos N, Semmer N, Elfering E, et al. Natural history of individuals with asymptomatic disc abnormalities in magnetic resonance imaging. Spine (2000) 25:1484–92.

11)  Garfin SR, Rydevik BL, Brown RA. Compressive neuropathy of spinal nerve roots. Spine (1991) 16:162–6.

12)  http://bja.oxfordjournals.org/cgi/content/full/99/4/461/AEM238TB1 Accessed July, 6, 2010.

13)  Watts RW, Silagy CA. A meta-analysis on the efficacy of epidural corticosteroids in the treatment of sciatica. Anaesth Intensive Care (1995) 23:564–9.

14)   Kirschner JS, Foye PM, Cole JL (2009). "Piriformis syndrome, diagnosis and treatment". Muscle Nerve 39 (1): 10–8.

15)  Goldberg RJ, Katz J.  A meta-analysis of the analgesic effects of omega-3 polyunsaturated fatty acid supplementation for inflammatory joint pain.  Pain. 2007 May;129(1-2):210-23.