Disk herniation
‍Anatomy of a healthy vertebra and disk

Definition

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

A herniated disk causes pressure on the nerve, pain and neurology

Pathology

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

The disc comprises a fibrous outer ring, the annulus fibrosis, and a jelly-like material filling the centre of the disk, 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.

Illustration of the different stages of disk herniation

Classification

Herniated disks 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 disk 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 disk 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 disk 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.

Left: Distal radius intraarticular, displaced fracture; Middle: Older distal radius fracture with callus formation; Right: Distal radius and ulna fracture, extraarticular and displaced

No 2.

Intra-articular fracture extends to the wrist joint (or articulation)

Extra-articular fracture is located outside of the wrist joint

Open fracture when bone fragments perforate the skin

Comminuted fracture when the bone breaks into multiple fragments

Non-displaced when the anatomical alignment of the bone is maintained or displaced when the bone fragments move apart.

Melone’s classification describes the characteristics of intra-articular fractures of the radius:

i    Stable fracture

ii    Unstable "die-punch"

iii   "Spike" fracture

iv Split fracture

v   Explosion injuries

Acetabular fracture of the pelvis

Acetabular fractures

These fractures are divided into:

Anterior pillar (not weight bearing part of joint)

Posterior pillar (often associated with dislocation of the hip including the weight bearing part of joint)

Transverse

Comminuted involving both column type 

Sacral / coccygeal fractures

The sacrum is a triangular-shaped bone formed by 5 fused vertebrae, which provide a posterior wall to the pelvic ring. At each side of the sacrum, the ala structures articulate with the ilium bones forming the sacro-iliac joints. Sacral fractures are usually parallel to the spine and can involve the ala. Less frequently sacral fractures may display an “H” shape, including a transversal fracture uniting both sides of the sacrum. Three zones are described where sacral fractures can occur that are along vertical lines relative to the alignment of the foramina. Sacral fractures may result in sacral instability and require treatment via sacroplasty (injection of bone glue into the fracture). Surgery is necessary in case of associated neurological symptoms.

Fractures of the coccyx involve the tailbone, the terminal portion of the spine situated below the sacrum formed by 3 to 5 fused vertebrae. Coccyx fractures occur when falling on a seated position. They are more common in elderly women and seldom require surgical treatment.

‍A traumatic impact is the most frequent cause of disk herniation

Causes

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

Disk degeneration is often the result of life style activities, work related and tissue wear and tear. It usually arises in older people due to disk fibrosis and narrowing of the disk 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 disk generates pressure to the nerves and possibly the spinal cord.

‍Frequent bending and carrying heavy weights is a significant risk factor for disk herniation

Risk factors

Disk 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 disks particularly in the lumbar section. 

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

Genetic factors cause anatomical changes in the vertebral endplate diminishing nutrition of the disk, 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.

Pain to the area of the spine affected by a disk herniation is the main symptom

Symptoms

The symptoms of a herniated disk 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 disks 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 arm

Loss 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

MRI of a patient with multilevel disk herniation to the cervical spine. Note the compression of the spinal cord at C4 and C5

Diagnosis

During clinical investigation, the doctor records the medical history including recent and past injuries, life style, physical and neurological symptoms. For a suspected disk herniation, the examiner carries out neurological assessment using the straight leg tests, Lasegue and Bragrad tests.

Radiological imaging, in particular MRI, allows to visualise at best the disks and the spinal cord. MRI is also more sensitive to identify minor fractures, which can be difficult to see on X-rays. Often CT scans and X-rays are used as first diagnostic tool.

Myelography with CT scan was used previously to determine the reduction in the diameter of the spinal canal (stenosis) following disk herniation, but has been replaced by MRI.

Discography is a functional test consisting in the injection of a contrast solution into the vertebrae, which may trigger pain similar to a disk herniation. This is followed by a CT scan to pinpoint the exact location and define the classification of disk herniation. However, discography is not considered sufficiently specific and is hardly used nowadays.

Laboratory tests. To exclude the contribution of other pathologies such as cancerous metastases growth to the spine, diabetes, infections and multiple myeloma, laboratory tests are useful for cancer biomarkers (e.g. PSA, prostate specific antigen), diabetes (glucose level), erythrocytes sedimentation rate (ESR) and multiple myeloma (Bence Jones proteins in urine).

Treatment

A cold pack helps relief pain and inflammation

Nonoperative treatment

In the absence of severe neurological symptoms, conservative treatment of the herniated disk 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 disk.

Vertebral fusion following surgical discectomy

Surgical treatment

Surgery is only recommended in a small population of patients with disk 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 disk and any disk fragments that compress the spinal nerves.

Laminectomy may be applied to remove the vertebral lamina for better access to the disk. 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 disk(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 disk. The nerves are pushed carefully to the side. The disk 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 disk. TLIF is specifically indicated for recurrent disk 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 disk(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. 

Autologous bone taken from the iliac crest of the pelvis

Bone graft

To accelerate bone healing and improve spine stability, various types of material are grafted following discectomy. Grafts include autologous (patient’s own bone) or heterologous (cadaver) bone, cement and other biological substances. Traditionally autologous bone graft is taken from the iliac crest of the pelvis and requires an additional surgery. Demineralised bone matrices (DBMs) are obtained from heterologous bone following the removal of calcium. They consist of gels rich in proteins that stimulate bone repair. Ceramics are synthetic calcium/phosphate materials with a consistency similar to bone. Bone morphogenic proteins are growth factors with a potent stimulating activity for bone formation.

Artificial disk replacement in the lumbar spine

More recently intervertebral disk replacement surgery has become popular in selected patients excluding those with more than two pathological disks, obesity, previous spine surgery, damage to vertebral facet joint, nerve injury and scoliosis. Artificial disks are mechanical devices of different shape used to replace the degenerated intervertebral disk. Materials include metals (titanium alloy, cobalt chromium) and medical grade plastic (polyethylene) often used in combination. This technology has been available in Europe, the US and Australia for over a decade with ongoing development. The artificial disk is inserted in the lumbar spine with an anterior surgical approach from the abdomen. On The day after surgery the patient is encouraged to walk but avoid extension of the spine. Pain improvement is achieved weeks to months post-surgery but may persist for longer.

Anterior cervical discectomy and fusion (ACDF)

Disk herniation at the cervical spine creates a strong pressure on the nerves of the neck possibly causing severe neurological symptoms. If conservative treatment is unsuccessful, surgery aims at decompressing the pinched nerves by removing the herniated disk, the bone fragments and possibly growing soft tissue (e.g. cancerous metastases). Additional fusion and disk replacement can be carried out in combination with discectomy. These methods can be applied to diverse pathologies of the neck such as fracture, cervical radiculopathy and instability. Anterior cervical discectomy followed by intervertebral fusion is the most frequent type of surgery for the pathology of cervical disks. The cervical spine is accessed via an incision to the frontal side of the neck, parallel to the spine. Once the herniated or degenerated disk has been removed the surgeon inserts the replacement material to obtain a normal anatomical distance and fuse the vertebrae above and below the pathological disk. This includes a cage filled with autologous (iliac rest) or heterologous bone graft. Fusion of two or more vertebrae can be achieved and in addition plates and screws are often used in multilevel fusions.

Posterior cervical lamino-foraminotomy

Lamino-foraminotomy denotes a small laminectomy with the surgical opening of the foramen (or foraminotomy from which the nerves exit the spinal cord. In this surgery the cervical spine is accessed from the posterior side of the neck. An incision of approximately 4-5 cm is done on the midline along the spine and the muscles and nerves are gently pushed to the side. The lamina of the vertebrae is excised to release the pressure to the nerve roots. Lamino-foraminotomy may occur without discectomy or intervertebral fusion. This facilitates the recovery after surgery.  

Minimal Invasive Spinal Surgery requires a small incision
A cage filled with bone material is inserted to replace the resected vertebral section

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 disk 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.

Massage therapy

Rehabilitation

Rehabilitation during conservative treatment of a disk hernia includes:

Massage / soft tissue manipulation

Ultrasound

Postural taping and postural support (cushions) to maintain optimal position of the shoulders, neck and lumbar spine and encourage alignment of the spine to avoid further damage and recurrent disc prolapse

Spinal traction

Cervical collar

Dry needling

Physical exercises (e.g. clinical Pilates) to reposition the disk, improve strength, core stability, flexibility and posture

Education on daily activity modification

Ergonomic advice on sitting, bending, carrying weights

Gradual return to strenuous activity program

Post-surgery recovery and rehabilitation

The hospital stay following PLIF, TLIF, ALIF and ACDF is normally quite short (a few days) or even just a day. Following discectomy of the cervical spine, without bone fusion, a neck brace is worn for months to allow bone healing. In case of fusion with metal instrumentation the stability of the spine is such that the use of braces is not necessary. The patient can resume normal activities paying attention to not over-stretch or add pressure to the spine. Rehabilitation usually commences a month post-surgery with a gradual step exercise supported by antiinflammatory treatment. General fitness condition is provided with walking and cycling followed by specific exercises to strengthen the muscles of the cervical and thoracic spine. A specialised physiotherapist will instruct the patient on how to modify daily activities to prevent excessive pressure on the operated vertebrae.

MISS reduces significantly the hospital stay and time of recovery. After surgery patients are rarely admitted to the ICU and remain in the hospital for maximum a week, if no complications arise. By preserving the integrity of the spinal muscles and other soft tissues, pain is minimised. Physical therapy can begin sooner accelerating the overall wellbeing of the patient. With spinal fusion the patient may require longer recovery before commencing strenuous physical activity. It is paramount to maintain a good alignment of the spine for a few months until the vertebrae have healed. Walking and other moderate activities are permitted.

A correct posture with a mild back exercise is critical to prevent a disk herniation

Prevention

Changes in life style and patients’ technique during physical activity are essential to prevent spinal disk herniation. Firstly, maintenance of physical condition will strengthen the muscles of the spine and alleviate the pressure to the vertebrae, disks and ligaments. Sitting, weight lifting, bending and twisting need to be performed with a correct posture (e.g. by keeping the spine straight and knees bent). Avoiding heavy weights, carrying heavy bags, losing excessive weight, and quitting  smoking are recommended to improve the health of the spine and prevent recurrent problems.