Prolapsed Intervertebral Disc

Written by: Babatunde Oremule from Manchester University,

Prolapsed Vertebral Disc

A prolapsed intervertebral disc is commonly referred to as a slipped disc. This description is a misnomer as what has actually occurred is rarely a "slipping" of the disc but a bulging out (herniation) of the inner part of the disc.

There is a strong genetic link to disc prolapse with twin studies indicating that a least 60% variance can be explained on genetic grounds and not the commonly apportioned environmental factors.

Environmental factors include:

  • Poor weight-lifting technique
  • Smoking
  • Occupations involving extended periods of sitting for example office work or taxi driving
  • Trauma
  • Age - "wear and tear" of the disc or "drying out" of the disc

 

Spine and Disc

As the name implies, the interverterbral discs are found between the vertebral bodies of the spine. The discs are rubber or jelly-like and act to cushion the spine when it bends. 

The discs are made up of the strong outer annulus fibrosus, and the gelatinous inner nucleus pulposus.

Herniation occurs posteriorly or posterior-laterally beneath the posterior longitudinal ligament. This can result in local oedema and pressure on the adjacent nerve root. A complete rupture of the disc can result in part of the nucleus pulposus lying free within the spinal canal.

Depending on on the structures involved, different symptoms may be experienced:

  • Pressure on ligament - Backache
  • Pressure on dural envelope of nerve root - Sciatica
  • Compression of nerve root - numbness, parasthesia and muscle weakness
  • Compression of Cauda equina - urinary retention (Rare, but it is a medical emergency as damage may become irreversible if left untreated for too long)

The disc can herniate at any level in the spine, but it must commonly occurs in the lumbar region, specifically at L4/L5 and L5/S1.

Clinical Features

The patient is typically a young and fit adult presenting with sudden onset back pain whilst lifting or stooping. They are unable to straighten up due to severe pain.

From the onset of the injury, the patient may present with:

  • Backache
  • Sciatica (characteristic pain in buttocks and lower limb)
  • Paraesthesia or numbness in lower leg or foot
  • Muscle weakness
  • Urinary retention

Backache and sciatica persists after the injury and is typically made worse by coughing or straining.

Observation

Sciatic Scoliosis - the patient may stand with a slight list to one side, increased during forward flexion

Range of back movements severely limited in all planes

 

Palpation

Tenderness in the midline of lower back

Paravertebral muscle spasm

 

Special Tests

Straight Leg Raise (SLR) - Tests for herination at L4/L5 or L5/S1 discs. This test is performed with the patient lying flat on their backs on the examination couch or bed.

  1. Raise one leg, keeping the knee joint completely straight, until pain is felt in the buttock, thigh or calf.
  2. Note the angle at which pain occurs. In normal circumstances pain is felt above 80-90 degrees. The test is positve when pain is felt between 30-70 degrees.
  3. Flexing the knee at this point will relieve buttock pain. Pressing on the popliteal nerve will reproduce the pain.
  4. Straighten the leg again and then lower the leg to below the angle where pain is felt. Dorsiflex the foot. If the pain is due to sciatica, this should reproduce the pain.

Patients with lumar herniation will have a limited SLR and it will be painful on the affected side. 'Crossed Sciatic Tension' - Raising the unaffected leg may cause sciatic tension on the painful side. This may be observed but is not a common finding.

Femoral Stretch Test - May be positive if nerve root of L3/4 is affected. This test is performed with the patient lying prone on the examination couch. 

  1. Flex the knee to 90 degrees
  2. Extend the hip

Pain is felt in the anterior thigh. This test is weakly positive in lumber disc herniation.

 

 

Neurological Examination

At the corresponding level of prolapse, you may find:

  • Muscle weakness (later wasting)
  • Diminished reflexes
  • Sensory loss

L5 impairment causes; weakness of big toe extension, weakness of knee flexion, sensory loss on the outer side of the foot and sensory loss on the dorsum of the foot.

S1 impairment causes; weak plantarflexion, weak eversion of the foot, a depressed ankle jerk reflex and sensory loss along the lateral border of the foot.

Cauda equina syndrome is a RED FLAG SYMPTOM. Cauda equina syndrome causes saddle anaesthesia about the anus, perineum or genitals and loss of anal sphincter tone or faecal incontinence. Patients may present with difficulty micturating.

 

Examination

Observation

Sciatic Scoliosis - the patient may stand with a slight list to one side, increased during forward flexion

Range of back movements severely limited in all planes

Palpation

Tenderness in the midline of lower back

Paravertebral muscle spasm

Special Tests

Straight Leg Raise - Limited and painful on the affected side.

'Crossed Sciatic Tension' - Raising the unaffected leg may cause sciatic tension on the painful side. his may be observed but is not a common finding.

Femoral Stretch Test - May be positive if nerve root of L3/4 is affected.

Neurological Examination

At the corresponding level of prolapse, you may find:

  • Muscle weakness (later wasting)
  • Diminished reflexes
  • Sensory loss

L5 impairment causes; weakness of big toe extension, weakness of knee flexion, sensory loss on the outer side of the foot and sensory loss on the dorsum of the foot.

S1 impairment causes; weak plantarflexion, weak eversion of the foot, a depressed ankle jerk reflex and sensory loss along the lateral border of the foot.

Cauda equina causes urinary retention and sensory loss over the sacrum.

Imaging

MRI is the most valuable method of imaging as it confirms the presence, level, size and extension of the disc herniation. Traditionally water soluble myelography and computed tomography (CT) were used to image the disc but these methods have proved to be less accurate and involve irradiation of the spine and pelvis. An X-ray must be performed to rule out any bone pathology.

Differential Diagnosis

  1. Inflammatory disorders - Ankylosing Spondylitis causes severe and more generalised stiffness and typical x-ray changes. Tubercolosis of the spine will produce a raised ESR.
  2. Vertebral tumours - Cause constant pain. X-rays show bone destruction or pathological fracture
  3. Nerve tumours - may cause sciatica but pain is continuous. CT or MRI may delineate the lesions

 

Treatment

The majority of herniated discs will heal themselves within 6-8 weeks and do not require surgery. Management problems arise if pain lasts longer than 8 weeks.

Non-Surgical or conservative management methods are usually tried first. These include:

  • Patient education on body mechanics
  • Physiotherapy
  • Heat therapy
  • Analgesics
  • Anti-inflammatory drugs
  • Oral or locally injected steroids
  • Weight loss
  • Smoking cessation
  • Reduction - continuous bed rest and traction for 2 weeks

Once non-surgicl methods have failed, discectomy or microdiscectomy is usually the treatment of choice.

Surgical management

The indications for surgical management are:

  1. Cauda equina syndrome which does not clear up within 6 hours of starting bed-rest and traction (Medical emergency)
  2. Persistent pain and severely limited straight leg raising after 2 weeks of conservative management
  3. Neurological deterioration while under conservative management
  4. Frequently recurring attacks

Rehabilitation

Rehablilitation is essential for patients once they have recovered from acute disc rupture or disc removal. The patient is taught isometric exercises in order to reduce the strain on their back. Light work in resumed after 1 month and heavy work after 3 months. If the patient fails to recover fully, heavy lifting should be avoided all together.

References

  • Solomon L, Warwick DJ, Nayagam S. (2005) Injuries of the Hip and Femur. In: Solomon L, Warwick DJ, Nayagam S. (Ed.) Apley's Concise System of Orthopaedics and Fractures. 3rd ed. (pp197-197) London: Hodder Arnold.
  • FEIG, D.S.,MD MSC, ZINMAN, B., MD, WANG, X., MSC and HUX, J.E.,MD MSC, 2008. Risk of development of diabetes mellitus after diagnosis of gestational diabetes.Canadian Medical Association journal, 179(3), pp. 229-234.