What is Sciatica?

Sciatica is a less-common type of low back pain (LBP) in which a patient typically experiences local lumbar spine, and nerve (sharp, electric, burning) pain travelling along the back of the thigh, leg and often into the foot (front or back). It is usually due to irritation of the L5, S1 and / or S2 nerve root, or the sciatic nerve itself. It can be caused by compression or chemical stimulation of  the spinal nerve(s) that leave the vertebral column along their path to the lumbosacral plexus, or the tributary branches to the sciatiac nerve.

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Sciatica is very often misused by patients and doctors alike to describe any low back pain (LBP) or LBP with pain travelling down the lower limb. This is partially true but can also describe many other LBP conditions without or without involvement of the sciatic nerve.

This page is a patient centred look at describing  what sciatic is, what causes it, what does it feel and look like, and how can it be treated successfully by a chiropractor and other health care providers.

Lumbar Spine Anatomy Go To
Causes of Sciatica (Etiology)Go To
How Common are sciatica and disc herniations Go To
Who Gets Sciatica Go To
Symptoms and Signs of Sciatica Go To
Do I need an X-ray or MRI Go To
Prognosis Go To
References Go To

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Lumbar Spine Anatomy 

The lumbar spine consists of five movable lumbar vertebral bodies (numbered L1 to L5) that sit atop the key-stone shaped sacrum (S),  which protect and house the spinal cord  in the vertebral canal. In the lumbar spine, the spinal cord travels not as a single rope of nerves, but in many individually packed nerve bundles (cauda equina = “horses tail”) that are destined to leave the vertebral column at a particular level of the spine.

Between each vertebra, closely behind the intervertebral disc, little round openings (neural foramina) serve as the exit points for this nerve bundles, which are labelled based on the level of the spinal cord they leave at: ie the L4 spinal nerve leaves the spine through the L4 neural foramen, which is located between L4 and L5

The spinal nerves (L1-L5, S1) nerve the spinal cord, branch into a front and back branch, and then form a complicated network of the front

branches called a (lumbrosacral) plexus. From these plexuses, nerves that travel into the lower limbs and pelvis, like the sciatic nerve, are formed and go to to provide sensation to the skin and motor nerves to the muscles.

Each spinal nerve has a corresponding myotome and dermatome (ie the L5 myotome and dermatome).

Dermatome: The area of skin supplied by a specific spinal nerve – cutting this spinal nerve would result in lost of sensation in this area

Myotome: The muscles that are powered by and correspond to a particular spinal nerve – cutting a particular spinal nerve would result in great losses in strength of this particular muscle group

Summary: Spinal cord becomes cauda equina in lumbar spine > forms spinal nerve > leave vertebral canal > moves through small neural foramina > spinal nerves joins complicated plexus > plexus forms peripheral nerves

EASY!!!

 

Cause of Sciatica (Etiology and Pathology)

Why is there pain where it is?

In any case of true sciatica, there is usually local low back pain and nerve pain, also known as radiculopathy.

Radicular nerve pain – why the pain travels away from the back

• results from stimulation of the spinal nerve as it leaves the spine through the small neural foramina or before it reaches the lumbosacral pleaxus
• The stimulation of the nerve can either be come direct compression or from chemical stimulation (chemical radiculitis) from the presence of local inflammation and inflammatory chemicals
• Chemical stimulation can occure from a local disc tear, disc herniation or other inflammatory process
• Direct compression of the spinal nerve can result from a number of cause including but not limited to intervertebral disc hernation or disc injury, spinal degeneration that narrows the canals through with the spinal nerve travels, or some sort of space occupying mass
• Stimulation of the spinal nerve causes the nerve to fire pain impulses that are interpreted by the brain as travelling along the entire path of that spinal nerve (along the dermatome)
• If the spinal nerve contributes to the sciatic nerve (L5,S1 mainly) then the brain will feel pain along the sciatic

  

  nerve as it travels down the back of the thigh, leg and into the foot

• The pain associated with radiculopathy will always display patterns of nerve type pain
• If the spinal nerve contributes to another peripheral nerve, the pain will be felt in that area – ie: L3 spinal nerve radiculopathy will be felt on the front of the thigh in the distribution of the femoral nerve
• Irritation of the sciatic nerve can also bring about symptom similar to those mentioned above, as is the case with piriformis syndrome or an entrapment of the sciatic nerve

Local low back pain

• Most cases of radiculopathy like sciatica also present with low back and pelvic pain that is not sharp, shooting, electrical nerve pain
• Local low back pain is felt as a result of inflammation or injury that activates pain nerve fibers of structures in the spinal canal causing localized (to the joint of injury) back pain
• Non-localized, non-radiating pain away from the joint of injury result from irritation of either ligaments, muscles or bones outside of the spinal canal. From either direct injury to a ligament, muscle or bone, like with a protective muscle spasm, pain may be felt in a large area across the lumbar spine and buttock

What is causing the pain?

Most cases of sciatica are attributable to disc injury. Whether there is a herniation of the intervertebral disc‘s central nucleous pulposis backwards into the spinal nerve (like the jelly in a jelly doughnut shooting backwards into the spinal cord), or a tear to the outside of the disc known as the annulus fibrosis, both can irritate or compress the spinal nerve

About 90% of movement of the lumbar spine occurs between L4 and S1. As a result, the L4-L5 and L5-S1 levels are most susceptible to injuries from routine movements of the spine, about 90 to 95 percent of compressive radiculopathies occur at these levels. This disc injuries will usually affect the L5 and S1 nerve roots and create sciatica symptoms.

Less movement occurs in the lumbar spine between L1-L4 and thus disc herniations are less common these levels, with L4 being the 3rd most common

Degernation and arthritis of the lumbar spine generally progresses with age, peaking sometime after fifty years old. Degeneration in lumbar spine can see disc degeneration with calcification and hypertrophy (enlargement) of the ligaments and joints of the spine.   These structural changes can cause narrowing of the neural foramina and subsequent impingement of the spinal nerve resulting in a nerve impingement. However, lumbar radiculopathy occurs less often with aging as a result of degeneration because of the progressive hardening of the intervetebral disc: the jelly in the jelly doughnut is more dehydrated and less likely to be extruded backwards into the spinal canal.

Other Nonskeletal_causes_LS_radiculopathy of lumbar radiculopathy are also possible.

 

How Common are sciatica and disc herniations

Its not as common as you think but chiropractors still see a lot of it! It represents about 3-10% of all types of low back pain and 5/1000 people will experience it in their lives.

Who Gets Sciatica

• Men and women equally
• Middle age (highest incidence in the fifth decade)
• Very rare before 20 years old
• retro- and prospective observational studies identified a higher incidence of sciatica or prolapsed disc among first-degree relatives than controls
• • in a population of patients presenting for surgery on herniated lumbar discs
• Lower incidence in joggers (whenpain free when beginning the study)
  • higher incidence in joggers with a previous history of sciatica symptoms
• Carpenters and machine operators > office workers
• A weak association between tobacco use and increased sciatica incidence
• Occupation risk factors:
  • awkward working position
  • working in a flexed or twisted trunk position
  • Working with the hand above the shoulder (ie painter and carpenter)
  • Driving (spine vibration)

   

 

Symptoms of Lumbar radiculopathy

The symptoms of a disc herniation or lumbar radiculopathy depend on the level of the spinal nerve effect: L2-L4 disc herniations will present very differently than the sciatica like symptoms from a disc injury affecting the L5 or S1 nerve roots.

Almost all cases of lumbar injury, including sciatica, will present with the following symptoms

• Local low back pain
  • Sharp, potentially burning or deep aching local low back pain (greater than one hand print in size)
• Pain usually of higher intensity
• Travelling pain
  • numbness, tingling, burning, or electric sharp pain travelling from the low back into the thigh, leg and sometimes foot
  • travelling distribution varies with the spinal nerve involvement
  • Travelling pain is NOT usually of a dull, or aching character
  • travelling pain in about 30-50% of cases
• Pain aggravated by straining (coughing, sneezing, defecating), bending forward
• Pain aggravated by movement (often flexion)

Sciatica Symptoms

L5 radiculopathy: 

• Most common
• back pain that radiates down back of the thigh and outside aspect of the leg into the foot
• Strength can be reduced in foot dorsiflexion, toe extension, foot inversion foot eversion
• Weakness of leg abduction may also be evident in severe cases due to involvement of gluteus minimus and medius
• Sensory changes is confined to the outside of the lower leg and top of the foot
• sensation in the web space between the first and second digits is typical
• Reflexes are generally normal, although the internal hamstring reflex may be diminished on the symptomatic side.
• aggravated by nerve root tension from straight leg raise: further aggravated by dorsiflexion

S1 radiculoapthy

• Pain radiates down the back aspect of the leg into base of the foot from the back
• Weakness of plantar flexion (gastrocnemius muscle) is specific.
  • There may also be weakness of leg extension (gluteus maximus) and toe flexion.
• Sensation is generally reduced on the posterior aspect of the leg and the lateral edge of the foot
• Ankle reflex loss is typical
• aggravated by nerve root tension from straight leg raise: further aggravated by dorsiflexion

Non-sciatic Nerve radiculopathy (L2-4 etc)

• There is marked overlap of the L2, L3, and L4 spinal nerves through the lumbosacral plexus and these radiculopathies are grouped together because they are difficult to differentiate
• Acute back pain is the most common presenting complaint
• Travelling pain around thefrom of the thigh and leg down into the knee
  • occasionally down the medial aspect of the lower leg as far as the arch of the foot
• Weakness of hip flexion, knee extension, and hip adduction
• Higher lesions may result in greater weakness of the hip flexors
• Sensation may be reduced over the front of the thigh down to the inside aspect of the lower leg
• A reduced knee reflex is common in the presence of moderate weakness.

 

Do I need an x-ray or MRI for my back

X-ray is not able to show most soft tissue problems like disc herniation or nerve impingements. Given that the most common cause of sciatica is disc herniation, x-ray is very rarely able to tell a doctor what the exact cause of your low back pain or sciatica may be. X-ray is still useful for ruling out certain conditions and is recommended on a case by case basis when prescribed properly.

In the case of MRI, consider the following example based on scientific studies:

You take 100 people sampled randomly from the street and take an x-ray and MRI. You then ask them if they have back pain. If you then try to accurately guess what people have back pain based on the imaging studies you performed, all the best research says that it is not possible to predict. More interestingly, almost 30% of the people who were taken from the street will demonstrate evidence of a disc bulge or disc herniation but will demonstrate no pain!

MRI will be able to tell a doctor the spinal level where there might be a disc herniation, degeneration or disc injury. MRI is useful in planning for surgery and for getting visual confirmation that reflects and explains your symptoms. However, it will not change how a physio or chiro approaches or guides your treatment. We always treat based on your symptoms, what aggravates and relieves your pain, and what treatment you respond best to. A picture of your back cannot tell us this information and is generally not needed because they rarely change a plan of conservative care.

 

Prognosis

The vast majority of patients will experience resolution of sciatica symptoms in weeks to months with conservative care.

• Conservative therapy (including bed rest, over-the-counter medication, physical therapy, activity modification, education etc) has been shown to help reduce the severity, intensity and duration of symptoms, AND reduce the progression to chronic low back pain
• In general, about 30% will see recovery by six weeks, 30% by three months and 90% by one year
• Between 10-30% will continue to have symptoms by one year’s time depending on what study you read but I believe it to be closer to 10%
• On average leg symptoms seem to last for about 8 weeks in severe cases
• Conservative care for at least six weeks is recommended in the US, Canada and most European countries before surgery is considered
• In a study published in the New England Journal of Medicine (2007), surgery and conservative care groups showed similar outcomes to care at one year’s time

 

 References

Hsu et al. (2015). Lumbosacral radiculopathy: Pathophysiology, clinical features, and diagnosis. In T. W. Post (Ed.), UpToDate. Retrieved from http://www.uptodate.com/home

Albert, Hanne B., and Claus Manniche. “The efficacy of systematic active conservative treatment for patients with severe sciatica: a single-blind, randomized, clinical, controlled trial.” Spine 37.7 (2012): 531-542.

Jacobs, Wilco CH, et al. “Surgery versus conservative management of sciatica due to a lumbar herniated disc: a systematic review.” European Spine Journal20.4 (2011): 513-522.

Peul, Wilco C., et al. “Surgery versus prolonged conservative treatment for sciatica.” New England Journal of Medicine 356.22 (2007): 2245-2256.

Tampier, Claudio, et al. “Progressive disc herniation: an investigation of the mechanism using radiologic, histochemical, and microscopic dissection techniques on a porcine model.” Spine 32.25 (2007): 2869-2874.

Soleimani, H., et al. “Conservative Management of Acute Lumbar Disc Herniation.” J Spine 2.134 (2013): 2.