LUMBAR DISC HERNIATION

A prolapsed or herniated disc is also known as slipped disc. In this condition tears develop in the outer fibrous covering of the disc called annulus, allowing the inner soft gelatinous nucleus pulposis to escape into the spinal canal and compress the lumbar and / or sacral nerves.

The most common location for tears is postero-laterally at L4 – L5 and L5 – S1 disc levels.  Disc herniation generally is preceded by a period of disc protrusion in which the disc bulges but the annular tear has not developed.

Disc protrusions, especially when the disc is loaded on standing and sitting, cause back pain with some leg pain. Once the disc has herniated and is compressing the nerve root, sciatica (leg pain radiating to the calf, ankle or toes) develops and the back pain may actually subside. Disc herniation is generally a result of age related degeneration with repeated minor trauma or the herniation is precipitated by an acute trauma or bending forward to lift a heavy weight. Repeated poor posture while sitting, weak back muscles, increased body weight and waist circumference, all contribute to disc herniation.

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SYMPTOMS

• Most patients with symptomatic lumbar disc herniation present with low back pain and pain in one or both legs, depending on the degree of prolapse and the side to which it is herniating.  Pain usually starts in the back and after an interval starts traveling down the leg (sciatica). This is generally a sign that the disc (annulus) has herniated and is compressing the nerve root on that side. Large, generally central, disc herniations or sequestrations, will cause bilateral leg pain and weakness and numbness of the legs or perineum and genitals with bowel and bladder dysfunction. This is called Cauda Equina syndrome and is treated as an emergency.

• Smaller disc herniations compressing a nerve may cause numbness or weakness of the muscle supplied by that nerve resulting in weakness of the big toe or foot  (plantar flexion or dorsiflexion). Asking the patient to walk on his or her toes and then heels can test this. Movement of the spine especially flexion may provoke sciatica and straight leg raising while lying supine will be restricted.

• Also, see back pain and sciatica

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INVESTIGATIONS

1. MRI of the Lumber spine (without contrast) is the most important investigation for disc disease. It shows clearly the spinal cord and the nerve roots arising from it, the vertebra and the intervening discs, and the soft tissues like muscles and ligaments, in relation to the spine.

• MRI also shows the degree of degeneration of the disc or discs, the extent of disc herniation and the degree of dural sac or nerve root compression. Though several discs may show degeneration, which is a normal part of ageing, the treating surgeon decides which of the disc herniations is causing the present symptoms, and treats accordingly. MRI scans done after administering an intravenous contrast material is required in patients who have had previous spine surgery at that level, to differentiate scar tissue from recurrent disc material or to rule out post – operative infection in discs called discitis.

1. X-Ray of the lumbar spine shows the vertebra and their alignment. Most commonly this is done in flexion and extension to check for any instability (listhesis). If listhesis is detected implants (titanium screws) will be required to stabilize the spine at the time of disc surgery. 

2. CT scan of the spine is done in certain cases where, after MRI and X-ray, some more information is required by the surgeon. This is particularly relevant in traumatic disc prolapse to look at associated injuries, to check for bone removal in case of previous surgery and to differentiate soft disc from bony outgrowths (osteophytes). 

3. Electromyography (EMG) / Nerve conduction test (NCV) 

• NCV is an electro-physiological test of the limbs that is done in certain cases where the diagnosis is in doubt, to rule out conditions like neuropathy that may develop as a result of diabetes, hypothyroidism or certain vitamin deficiencies.

• EMG can give an indication of which nerve root may be involved by compression from a disc resulting in acute or chronic changes on EMG. This may help decide levels of surgery in multiple disc prolapse.

 

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TREATMENT OPTIONS

• While the symptoms are mainly confined to the back the treatment is generally conservative (non-surgical).  Bed rest is not recommended beyond 24 to 48 hours at the most. 

• Conservative treatment of disc prolapse is with physiotherapy and drugs like NSAID’s and Pregabalin/ Gabapentin.  Most of literature will support early relief of symptoms and early return to work for those patients of herniated lumbar disc who have undergone surgery. This surgical advantage of surgery versus conservative treatment persists for 4 years following surgery according to the SPORT trial and upto 10 years according to the Maine Lumbar Spine Study Group. On the other hand there is also literature supporting conservative treatment for this condition. However both surgery and conservative treatment has been found to be effective in the long term. The choice of treatment will be ultimately decided by the patient depending upon the severity of their pain, their lifestyle, need to return to work, etc, after thoroughly discussing the risks and benefits with their surgeon. Patients with neurological deficit need surgery and those with saddle anaesthesia and bladder and bowel  involvement  need surgery urgently.

• Once back pain and sciatica has persisted beyond 4 to 6 weeks or weakness of the leg or foot develops one has to consider minimal invasive spine surgery (MIS) options i.e. micro-discectomy or endoscopic discectomy. These can be done through a small incision in the back. The microscope or endoscope is used for better illumination and magnification. Spinal fusion or artificial disc replacement is not performed for simple disc prolapse. Spinal fusion is only necessary if there is instability (listhesis). The patient can be mobilized the same or next day and goes home within 24 to 48 hours of surgery.

• Minimal invasive surgical options for herniated or sequestrated lumbar disc are:-

  • Percutaneous discectomy : in this procedure the disc decompression is done through a needle and is the least invasive of  all disc surgeries. However it is for those patients with a contained disc i.e. a disc that is bulging and causing symptoms but has not ruptured the outer capsule to cause herniation. The centre of the disc  is first fragmented using instruments or laser or radiofrequency current and then removed through the needle. Patients get symptomatic relief as the intra-discal pressure reduces. Long term results of this procedure are not available and may be similar to conservative treatment. 

  • Endoscopic discectomy: This is done through a small incision using an endoscope with the patient under local anesthesia or general anesthesia. Through the small skin incision a port is introduced through which is passed the endoscope and discectomy instruments. In many cenres this is done as an out-patient procedure.

  • Microdiscectomy: This is the standard neurosurgical procedure for disc prolapse and is done under general anesthesia under microscopic magnification and illumination. With good case selection the success rate for the surgery is 95 to 98 %. Microdiscectomy avoids an extensive bone removal (laminectomy) that has been the traditional operation for disc excision and remains a standard orthopedic procedure in many centres.

  • Laminectomy: Most orthopedic surgeons prefer to remove herniated discs by a procedure called laminectomy where part of the lamina (bone in the posterior part of the spine) is removed to access the disc. Experienced spine surgeons however prefer not to remove any bone to avoid the possibility of spinal instability (listhesis) in later years.