CERVICAL DISC HERNIATION
Cervical disc herniation is a condition when degenerated cervical intervertebral joint slips into vertebral canal casuing nerve root and spinal cord compression
Human head and neck and are supported by cervical spine which consists of seven vertebral bones and joints between them. Spinal cord is passing through the vertebral canal inside cervical spine. At each vertebra level spinal cord gives off a pair of nerves that travel in intervertebral foramen to exit the spine. These nerves provide signals to and from the spinal cord.
Each pair of vertebral bones are connected with one big disc joint and two smaller facet joints. Each disc joint has a soft and elastic inner core called nucleus pulposus and tough outer ring – annulus fibrosus. Nucleus is made up of unique, gel-like substance and serves as an elastic pillow between the neighbor bones. It provides mobility to the spine and serves as a shock absorption buffer. With aging the nucleus pulposus loses water, shrinks and breaks to pieces. Fragmented parts break though the annnulus fibrosus and slip into the canal. This condition is called cervical disc herniation. Once in the canal herniated parts compress the spinal cord and nerves. When a cervical nerve root is compromised this condition is called cervical radiculopathy. Below is schematic picture demonstating disc herniation compressing a nerve root as it takes exit from the spine.
Spinal cord compression is referred as myelopathy. This type of myelopathy is called cervical spondylotic myelopathy. Myelopathy is a more severe condition than radiculopathy and should be treated promptly.
Disc joint degeneration may progress without herniation and the nucleus disappears almost completely. This leads to decrese in intervertebral disc height. In other words vertebral bones become close to each other. Nerve exit foramina therefore get narrower resulting in nerve pinching. With lack of support from the center, load shifts to outer portions of the vertebral bones. This results in formation of extra bone tissue to handle the increased load. Newly formed bone spurs or osteophytes additionally compress the spinal cord and nerves. This condition is called cervical stenosis (literally narrowing). Cervical stenosis is a chronic process and takes several years to fully develop. In some instances cervical stenosis produces very little symptoms because spinal cord and nerves have time to adapt. However cervical spondylotic myleopathy is very common in cervical stenosis. Cervical disc herniation may develop on top of cervical stenosis and aggravate chronic symptoms.
Cervical radiculopathy presenting as pain in the neck radiating down the arm is the most common symptom of cervical disc herniation. Sometimes the pain may also spread to the back of the neck, head, and between shoulder blades.
Radiculopathy is more frequent in disc herniation and myelopathy is mostly seen with cervical stenosis. Typical radicular pain starts in the neck and radiates to the arm. Depending on the involved nerve arm pain location may vary. Numbness and weakness usually develop when there is significant compression of the spinal cord and nerves compromising their function. Numbness may not be appraciated by patient since theys have pain. But patients are ususally well aware of weakness (paresis). In advanced cases muscle wasting (atrophy) may develop. Cervical spondylotice myelopathy presents with combination of muscle weakness (paresis) and ataxia. Paresis may be subltle so the patients may have not apparetn weakness. Rather fine motor functions can be compromised resulting in clumpsyness. Ataxia or loss of body balance is a very frequent finding and the patients’ walk resemble drunken person’s walk.
In rare cases bone spurs may cause compression of the vertebral arteries supplying the brain. These patients therefore suffer from insufficient blood flow to the brain and usual symptom is dizziness, vertigo and even unconscious falls. Bone spurs may develop in front of spine, compressing the esophagus. In these cases, patients experience swallowing difficulty of dysphagia.
Obtaining the history of disease and meticulous examination is sufficient to suspect the diagnosis. Neurological examination with complete motor and sensory assesment is absolutely necessary since patients might be unaware of their deficits. Radiological examination like cervical MRI, X-ray and CT is very important in establishing the diagnosis. X-rays show cervical vertebral bones, their aligmnent, narrowing of the disc spaces, bone spur formation, and deformity.
However soft tissue is not visible on X-ray. MRI on the other hand is an excellent tool in demonstrating soft tissues like spinal cord, nerves and ligaments.
EMG, nerve conduction and evocked potential studies can be perfomed to confirm the presence of radiculopathy and myelopaty if suspected.
Treatment of degenerative cervical disc disease depends on severity of symptoms. Initially, patients presenting with pain are usually managed with conservative means like pain medications, chiropractic maneuvers, physical therapy etc. Local injections and radiofrequency ablation might be helpful in selected cases.
Failure to address pain on long term and neurological deficits are indications for surgical treatment. The surgery may be done from the front (anterior) or from the back (posterior) depending on the patient condition and surgeon’s choice. When surgery is performed from the front it is called anterior cervical discectomy and fusion (ASF or ASDF). Damaged nucleus pulposus is completely removed and all compression is eliminated by removing soft and hard tissue compressing the nerve roots and spinal cord. Disc joints then are either fused together . Cervical fusion is the most widely used procedure. A cage filled with bone tissue is inserted between the vertebral bones into the space created by removal of nucleus. The surgeon then uses metallic plate and screws to hold neighbor bones together to provide stability. Newly formed bone tissue bridges the adjacent vertebral bones and eventually fusion develops.
An alternative technique is disc prosthesis. It is also called motion preservation and it is a relatively new technology. Instead of fusing the vertebral bones together and losing mobility at that segment of cervical spine, an artificial joint is placed which serves as a substitute for removed disc joint. This way the surgeon is able to preserve the motion. Preserving the motion is very important since adjacent joints do not experience additional load as in fusion and therefore the likelihood of developing additional disc herniations is lower than with fusion.