Definition

Herniation of the intervertebral disc, also named disc prolapse, ruptured disc or slipped disc, occurs when the gelatinous content of the disc protrudes towards or outside the rim of the disc.

Pathology

Disc herniation is one of the most frequent causes of back pain mostly affecting the lower spine. The intervertebral disc is a cushion-like structure positioned between the vertebrae to absorb stress to the spine and facilitate movement.

The disc consists of a fibrous outer ring, the annulus fibrosis, and a jelly-like material filling the centre of the disc, the nucleus pulposus.

The initial stage of the condition involves the herniation of the nucleus pulposus towards the annulus fibrosis. The annulus fibrosis can present one or more tears or a complete rupture causing the total or partial release of the nucleus pulposus into the outer space. This can produce pressure to the spinal cord and nerve roots. Disc herniation causes local inflammation and possible nerve damage resulting in significant pain, clinically known as radiculopathy, and in some cases severe neurological symptoms in form of paresis, e.g. foot drop.

Classification

Herniated discs may be defined as bulges, protrusions, extrusions or sequestrations, depending on the contour of the displaced material, their volume and their distance from the centre of the disk.

Bulge & Protrusion (degeneration): the disc bulges without rupturing the annulus fibrosis.

Prolapse: the nucleus pulposus is displaced to the outermost layers of the annulus fibrosis.

Extrusion: the annulus fibrosis is perforated and the gelatinous material is pushed to the epidural membrane enclosing the spinal cord.

Sequestration (subtype of extrusion): The disc is fragmented and can be found as free floating material within the spinal canal causing significant pain and neurological symptoms.

Additional classification of disc herniation relies on the type of displaced material (nuclear, cartilaginous, bony, calcified, ossified, collagenous, scarred, desiccated, gaseous or liquid), and whether the material is contained within the intact annulus or uncontained when outside its boundaries. The consequent compromise of the spinal canal by a herniated disc is graded as mild if less than 1/3, moderate if 1/3 to 2/3, and severe if over 2/3 of the spinal canal space is obliterated.

Causes

Trauma, either single or repeated, is the most common mechanism of disc herniation caused by the rupture of the annulus fibrosus. This leads to the protrusion and/or extrusion of the disc material into the vertebral canal. When the disc has collapsed the space between the vertebrae is reduced.

Disc degeneration is often the result of life style activities, work related and tissue wear and tear. It usually arises in older people due to disc fibrosis and narrowing of the disc space, deterioration of the annulus, sclerosis of the vertebral endplates and presence of bony growths (osteophytes) in the inner space of the vertebrae. The prolapsed disc generates pressure to the nerves and possibly the spinal cord.

Risk factors

Disc herniation is most common in men between 30 and 50 years of age and in all ageing individuals. These are the main risk factors:

Overweight/obesity increases pressure on the spine and intervertebral discs particularly in the lumbar section.

Smoking reduces peripheral blood circulation and diminishes blood supply to the disc, facilitating its degeneration.

Genetic factors cause anatomical changes in the vertebral endplate diminishing nutrition of the disc, and predisposing to subsequent pathological alterations.

Poor physical fitness including:

Sedentary lifestyle weakening the supporting spinal muscles

Frequent driving

Inadequate sporting technique Improper posture when weight lifting or sitting at desk

Sudden pressure to the spine

Repetitive strenuous activities in labourers performing heavy physical work.

Symptoms

The symptoms of a herniated disc differ depending on the section of the spine where it occurs. Local pain is the most frequent sign. It can be acute or increase gradually extending to the limbs (e.g. disk herniation to the lower spine causes pain to the leg and foot known as sciatica). Below is a list of symptoms, which can present either alone or in combination for herniated discs of the cervical and thoracic/lumbar spine as they are more frequently affected.

Cervical spine

Neck pain  

Burning pain in the shoulders, neck and arm

Muscle pain between neck and shoulder (trapezius muscles)

Shooting pain extending to the arms

Headaches

Weakness in one arm

Tingling ("pins-and-needles" sensation)

Numbness in one armLoss of bladder or bowel control in serious pathology

Thoracic / Lumbar spine

Thoracic / Lower back pain

Burning pain in the buttock, thigh, calf and foot

Shooting pain to one or both legs

Weakness in one or both legs

Tingling ("pins-and-needles" sensation)

Numbness in one or both legs

Loss of bladder or bowel control in severe cases

Treatment

Nonoperative treatment

In the absence of severe neurological symptoms, conservative treatment of the herniated disc is recommended. This includes pain relief medications together with a short period of bed rest, avoiding prolonged sitting, bending, weight lifting or any activity, which puts pressure to the spine.

The use of oral non-steroidal anti-inflammatory drugs (NSAID) is prescribed to dampen local inflammation.

Epidural injection of more powerful steroids is advised if symptoms are more severe. Other conservative measures include application of hot or cold packs, massage, myotherapy and acupuncture. Once the acute phase has subsided, physical therapy can begin to gradually strengthen the muscles of the spine and abdomen to support the spine and alleviate pressure on the disc.

Surgical treatment

Surgery is only recommended in a small population of patients with disc herniation when conservative treatment fails to resolve ongoing pain or in case of aggravation of neurological symptoms. Surgery is usually performed following antiinflammatory therapy.

Microdiscectomy is the most frequent operation to the lumbar spine and consists in the removal of the herniated portion of the disc and any disc fragments that compress the spinal nerves.

Laminectomy may be applied to remove the vertebral lamina for better access to the disc. Microdiscectomy utilises a special microscope to view the spinal canal, the disc and local nerves. The combination of a small incision and a microscope reduces the risk of damaging the nerves and surrounding tissue.

Spinal fusion is a more extensive surgical procedure whereby two or more vertebral bodies, separated by the pathological disc(s), are fused together with metal implants filled with bone replacement material or allograft from a donor bone. This surgery reduces pain but limits the flexibility of the spine, as the fused vertebrae become a single bone. Numerous surgical approaches are available for spinal fusion and mostly depend on the location of the access to spine:

Posterior (from the back)

Lateral Anterior (from the ribcage or abdomen)

Posterior lumbar interbody fusion (PLIF)

‍Posterior lumbar interbody fusion is the welding of two or more vertebrae via an opening in the back of the spine. Following a midline incision of the skin along the spine and the separation of the muscles, a laminectomy is performed to create space to reach the disc. The nerves are pushed carefully to the side. The disc is resected and replaced with a spacer or cage that is introduced between the vertebrae. The cage is filled with bone graft prior to implantation. To finally stabilise the vertebrae, screws are inserted into the pedicles of the upper and lower vertebrae and then connected with bars or plates.

Transforaminal lumbar interbody fusion (TLIF)

Transforaminal lumbar interbody fusion is a variation of PLIF in which the surgeon creates an opening to the lateral side of the spine. This prevents damage to the muscles and excessive displacement of the nerve roots. This technique also permits to better decompress the nerve roots, so called rhizolysis, by excising the facet joints as well as facilitating the removal of the degenerated disc. TLIF is specifically indicated for recurrent disc herniation and foraminal stenosis (reduction of the space of the spinal cord canal).

Anterior lumbar interbody fusion (ALIF)

Anterior lumbar interbody fusion is achieved by accessing the spine from the abdomen (laparotomy) or through the side of the abdomen (lumbotomy). These approaches reduce the risk of damaging the nerves but require caution to avoid injuries to the vessels, including the aorta, the intestine or other organs (spleen). Following the removal of the disc(s) the space between the vertebrae is filled with bone graft, metal or plastic spacer. Frequent is the use of a metal cage, filled with bone graft. Subsequently, metal rods in combination with plates and screws are placed posteriorly to fuse the adjacent vertebrae.

‍

Minimal/less Invasive Spine Surgery (MISS/LISS)

Minimal or less invasive spine surgery was developed in the 1990s as an alternative to open surgery to diminish damage to the muscles surrounding the column and decrease the incision size. This technique reduces bleeding, patients' length of stay in hospital and facilitates recovery. MISS comprises a number of techniques usually performed by experienced surgeons who rely on sophisticated tools. Through a small incision the surgeon inserts a retractor to move aside the soft tissues and reach the spine. Surgical instruments are long and fine, especially made to fit into the retractor. Using this canal, the surgeon extracts fragments of the injured disc or bone, inserts implants and performs the vertebral fusion. Due to the limited view of the surgical area, a fluoroscope is used to shoot real-time X-rays of the spine, which are displayed on a screen. A microscope is often used to magnify the images of the operating field. When microdiscectomy has been completed the retractor is removed and the muscles allowed to return to their position. MISS is applied to a number of spine procedures in modified forms, including discectomy, lumbar or thoracic spine fusion and reconstruction of the vertebrae following trauma or neoplastic/metastatic growth.