LUMBAR DISC HERNIATION

 

Definition

Lumbar disc herniation is a condition when degenerated intervertebral disc material slips into the spinal canal causing compression of the lumbar nerve roots. 

 

Anatomy

Human spine is the major supporting structure in the body. It is composed of vertebral bones and joints connecting them. Spine is arbitrarily divided into four parts: cervical, thoracic, lumbar and sacral. Coccyx is a small bone attached to the sacrum at its lowest part. Lumbar spine is composed of five lumbar vertebra and joints between them.


 

Illustration of human body with spine and nerves shown through transparent body

 

These joints provide mobility to the spine. Each vertebral bone connected to its neighbor with three joints. Disc joint is the major load-bearing structure of the spine.  It is composed of core gelatinous component called nucleus and a stronger external ring. Nucleus is very rich with water and is very elastic. It provides cushion for the bones as well as allows bones to move. With time the nucleus undergoes “wear and tear”, loses its elastic properties and breaks to pieces. This process is called degenerative disc disease. 

 

Normal and degenerated lumbar disc and vertebrae

 

 

With loss of properties the degenerated nucleus cannot hold the body load and usually at this stage patients have low back pain. Most of the patients usually do not advance to further stages. However, in some instances one of these fragments can make a tear in the outer ring and slip out. This condition is called lumbar disc herniation. Ruptured disc fragment usually compresses the nerve passing in the spinal canal causing pain, numbness and weakness in the leg. This condition is called lumbar radiculopathy. There are various stages of lumbar disc herniation. Initially the degenerated nucleus makes a small bulge which later may advance a make disc protrusion. At this stage the pain is usually the main symptom. With further advancement disc herniation progresses to extrusion and even to complete sequestration of the ruptured disc fragment.

The fragmented parts may remain inside the disc joint. With time, they completely tear off and since there is nothing to hold, entire joint collapses under body weight. Vertebral bones experience greater pressure under this condition and start developing bone spurs or lumbar osteophytes. The whole process is slow and takes years to develop but eventually spinal nerves get pinched. This condition is called spinal stenosis. Spinal stenosis is slightly different from lumbar disc herniation because it takes long period to develop and usually the patients’ neurological status is good. Usually the patients cannot walk long distances. In some cases, disc joint laxity causes back bones to slip. This condition is called lumbar spondylolisthesis or simply slippage. 

 

Classification

 

 

 

Animation of lumbar disc degeneration process

 

There are several stages of lumbar disc herniation. Healthy nucleus is very elastic and keeps two adjacent vertebra at normal distance. With degeneration disc desiccates, shrinkers and looses its elastic property which result in overall joint height decrease. Such a collapse lead annulus fibrosus to bulge outwards narrowing the canal. At this stage back pain is usually the main symptom. Later fragmented nucleus parts may cause rupture in annulus fibrosus and advance outward. This condition is called disc protrusion. Radiculopathy may be present at this stage. With further advancement disc herniation progresses to extrusion and then to complete sequestration of the ruptured disc fragment.

 

Lumbar disc degeneration sequence

 

 

Symptoms

Symptoms of the disease depend on the duration and extend of the process. Degeneration alone causes low back pain. Mechanical nature of the pain is very specific to this condition. Pain is aggravated by increased load and relieved by resting. Bending forward combined with heavy object lifting may produce significant pain and trigger an acute low back pain attack. Usually these attacks last from several days to several weeks and respond very well to resting and pain remedies. Pain might be also aggravated by cold and thats why is usually worse during winter season. 

 

A man with back pain after heavy lifting holding his back

 

Presence of leg pain indicates nerve root compromise and is an early sign of radiculopathy. Usually this type of pain originates in low back region and radiates to the leg. Presence of the pain in one extremity is typical finding yet both legs may be affected too. Extend of leg pain depends on nerve root involvement. Physicians may diagnose the affected nerve root by asking the patient's to localize leg pain. Advanced compression causes nerve function compromise and results in loss of sensation (hypoesthesia) and weakness of the leg muscles (paresis). These symptoms are referred as neurological deficit and should alarm patients and physicians and should be treated promptly. Delays in diagnosis and treatment of neurological deficits may cause permanent loss of neurological function. 

Lumbar stenosis causes specific set of symptoms that are different from lumbar disc herniation. Since the process is very slow a classical radiculopathy is not usually present. Patients often experience “neurogenic claudication” – which is characterised by inability to walk long distances without rest. As disease progresses walking distances become shorter significantly compromising patient's quality of life. Usually both legs are involved though one side is affected more than the other.

 

Diagnosis

The diagnosis of lumbar disc herniation is done by meticulous clinical examination and radiological assessment. History of the disease and physical examination are the most crucial parts of patient's management. Not only clinical examination is important for evaluation of neurological status but also it provides crucial information for correct treatment plan. 

Radiological evaluation is very important part of assessment. MRI of lumbar spine is the diagnostic test of choice. It shows the number of affected discs, extend of disc degeneration, presence of herniation and nerve root compression. Disc degeneration is best appreciated on T2 weighted MRI scans. Since water loss is an essential part of degeneration the damaged disc will appear dark while normal disc are white. 

 

Lumbar disc herniation MRI showing the difference between normal and degenerated discs and herniation itself

 

X-ray and CT scans can also performed for evaluation especially if bone structures need to visualized. X-rays provide overall information about lumbar spine alignment, presence of deformity, bone spurs, narrowing of the disc spaces, vertebral slippage etc. CT scans provide more detailed information about bone structures than X-ray but require more radiation exposure. 

EMG, nerve conduction and evoked potential studies can be performed in some cases to confirm the presence of radiculopathy if diagnosis is doubtful. These studies are especially helpful in distinguishing radiculopathy from peripheral nerve compression syndromes. 

 

Treatment

Initially disc degeneration and lumbar herniation are treated conservatively. Pain killers, resting, physical therapy, chiropractic manipulation, acupuncture and other means are usually effective in most cases. Patients should be noted that degeneration is irreversible process and these treatment options provide symptomatic relief. Therefore, they do not provide long term benefit. In order to decrease the speed of degeneration and avoid surgery patients should lose weight, avoid smoking, strenuous activity especially associated with significant mechanical load to lower back. 

In some patients, spinal injections and radio-frequency ablations may alleviate symptoms. Epidural steroid injections might very helpful in cases of acute pain. But it should be reserved for cases when other treatment options fail to alleviate pain. It was shown that injected steroids cause fibrosis in epidural space in long term. The nerves get attached to spine and loose their mobility causing pain. Another disadvantage of epidural fibrosis is lowering success of surgery. It was clearly demonstrated by SPORT trial (spine patient outcome research trial) that patients received steroid injections show lesser improvement with surgery. 

Advanced disease is treated surgically. Indications for surgery are follows: the presence of neurological deficit (paresis with or without hypoesthesia), inability to control pain with non-surgical treatments, significant compromise in quality of life due to degenerative disc disease. There are various surgical solutions for these patients and the optimal treatment is based on individual conditions. However, the main goal of the surgery is to relieve the pressure from the nerves. Discectomy or removal of the disc is the cornerstone of lumbar disc herniation treatment. There are various forms of discectomy: open discectomy, micro-discectomy, endoscopic discectomy, percutaneous discectomy etc.

 

Types of disc surgery in comparison

 

All these procedures relieve the pressure from the nerves by removing the herniation that causes the nerve compression. Additional discectomy is performed in order to decrease the likelihood of future herniation. Lumbar discectomy is a very effective method of treating disc herniation. Yet there are two major drawback of this technique. First intervertebral joint degeneration is not addressed by this surgery. The affected disc joint may continue to cause low back pain. Second disadvantage is the possibility of recurrent disc herniation. The risk of future re-herniation is especially high  in patients with large herniations with wide annulus ruptures. The surgeon may need to put hardware in lumbar spine depending during surgery. In these cases, the lumbar stabilization is performed.

 

Lumbar fusion with pedicle screw and rod technique

 

Usual indications for stabilization are spinal instability, recurrent herniations, and intend to avoid future herniations. Stabilization is usually performed by using interbody technique. In time stabilized segment of spine fuses into one solid piece of bone thus effectively eliminating the risk of future disc problems. It should be noted that fusion eliminates motion at the portion of spine. Therefore neighbor levels experience increased load and may degenerate faster. Thus the risks and and benefits of fusion surgery should be weighed carefully prior to the surgical procedure.