Acute intervertebral disc prolapse

Introduction


Intervertebral disc comprises of 3 important components :



1) cartilage end-plate 2) nucleus pulposus 3) annular fibrosus

The cartilage end-plate is a thin articular plate situated in between the adjacent vertebral bodies and the disc proper. The disc receives nutrition from the vertebral bodies via these cartilage end-plates.

Nucleus pulposus is a gelatinous substance located slightly posterior to the central axis of the vertebra. It is surrounded by concentric fibro-cartilaginous rings, known as annular fibrosus.

In front and behind of the vertebral bodies and intervertebral disc are covered by strap ligaments, known as the anterior and posterior longitudinal ligament.

Pathophysiology


What we meant by disc prolapse is actually the protrusion or extrusion of the nucleus pulposus through a rent in the posterior part of annular fibrosus.

Due to softening and fragmentation of the nucleus pulposus, weakening and disintegration of the annular fibrosus at it's posterior part, initially there is bulging of the nucleus pulposus through the annular fibrosus, where it is known as disc protrusion.

Later, as the nucleus pulposus protrudes through the defect of annular fibrosus, where it lies under the posterior longitudinal ligament, and yet to lose it's contact with the parent disc, this is known as disc extrusion.

As the nucleus pulposus lose it's contact with the parent disc, which involves stripping off the posterior longitudinal ligament, the nucleus pulposus becomes a free fragment within the spinal canal. This is known as disc sequestration.

Subsequently, there'll be fibrosis of the residual nucleus pulposus, and degeneration, calcification and fibrosis of the sequestered disc. As degenerative changes takes place in the intervertebral disc, the height of the disc is reduced, causing incongruity of the facet joints and resulting in secondary degenerative arthritis. At the site where the posterior longitudinal ligament is being stripped off, osteophytes or bony spurs are formed.

Disc prolapse will also results in nerve root compression. For eg, if disc prolapse occurs at the level in between L4-L5, L5 nerve root will be involved. The commonest site where a disc prolapse can occur is in between L4-L5, in case of a lumbar spine, whilst in cervical spine, the commonest is between C5-C6.

Clinical features


Disc prolapse can occur in any age group, however it is rare in both extremes of age.
Typically it involves a fit adult, aged around 20-45 years old (though may complain of previous h/o of mild recurrent back pain), after lifting heavy weight or being in a stooped posture (after sneezing), complains of severe back pain and inability to straighten the back.

A day of two later, there is parasthesia, tingling and numbness over the leg or foot, pain radiating from the back to the thigh or buttocks (sciatica), which is aggravated by coughing and straining.
Sometimes, it may be associated with muscle weakness, and rarely resulting in Cauda Equina Syndrome leading to urinary incontinence.

On examination, the posture of the patient is typically stooped, with a tilt to one side.
The knee of the affected side is usually slightly flexed, where attempts to extend the knee joint will aggravates the bending of spine.
All movements over the spine is restricted.
The patient will be tilting more towards one side when ask to bend further forwards.

On palpation of the back, there is diffuse tenderness over the lumbar region, paraspinal muscle tenderness and etc. Then sciatic stretch test is done :


1) Straight leg raising test (SLRT) : While doing the SLRT, the knee must be absolutely straight. Slowly raise the lower limb and note at which angle the patient starts complaining of sciatica. Usually the test is considered positive if the angle of < 60 degrees.

2) Then, try dorsiflex the patient's foot and look at how this maneuver intensifies the pain.

3) At the angle where the patient complains of pain, slightly flex the knee joint and there should be some relieve of pain. Then, press over the site of lateral hamstring to compress the common peroneal nerve and this results in the pain recurrs at new intensity


4) Alternatively, one can perform the lasegue's test. Flex the knee joint fully and the hip joint up to 90 degrees, slowly extend the knee joint. This is not possible if the sciatic nerve is stretched.

5) Occasionally, there might be a +ve cross SLR, where raising the normal lower limb causing pain over the affected side.

6) In case of high or mid-lumbar disc prolapse, a femoral stretch test can be positive. Perform it when the patient is in prone position, and passively hyperextend the lower limb of the affected side.

Neurological examination is done, and interpret as follow :

If there is weakness of the plantar flexors, sensory deficit over the tip of little toe, and sluggish/absent ankle jerk, it points towards a prolapse that occurs in between L5 and S1. (S1 nerve root is involved)

If there is weakness of EHL muscle/dorsiflexor of the ankle joint, sensory deficit over the first web space, normal ankle joint, it is suggestive of a prolapse that occurs in between L4 and L5. (L5 nerve root is involved)

If there is weakness of the knee extensor, sensory deficit over medial malleolus, and knee jerk is sluggish/absent, it is suggestive of a prolapse that occurs in between L3 and L4. (L4 nerve root is involved)

Investigations


1) X ray spine is not helpful. It is essentially normal, unless if there is repeated attacks of PID, the joint space may be reduced, osteophytes may be seen.

2) Myelography used to be the tool to confirm the diagnosis of PID, but currently it is abandoned due to :

A/E : headache, dizziness, nausea and CNS infection after the procedure
Hypersensitivity towards the contrast material that is used, causing anaphylaxis.
Unable to detect far lateral disc prolapse (lateral to intervetebral foramen)

3) CT and MRI is a more reliable mode for spinal imaging nowadays.

Management


In cases of acute PID, conservative treatment is employed.
Patient is advised to have bed rest by lying down supine, and pelvic traction of 10 kg is applied.
Analgesics such as indomethacin is given.

Within 2 weeks, 90% of the cases will recover spontaneously.
If symptoms didn't resolve, epidural injection of corticosteroids or local anesthetic can be given.

Operative intervention such as laminectomy, or microdiscectomy can be done if :

1) Neurological deterioration during conservative treatment
2) No improvements after 6 weeks of conservative treatment
3) Cauda Equina compression syndrome with no improvement after 6 hours of conservative management - emergency

Category: Orthopedics Notes