There are many causes of neck pain and it is very common to have an episode of neck pain within one's lifetime. However, over 90% of this pain is self-limited or resolves without treatment. The first division, in determining where the pain comes from, is to think of the pain as either intrinsic, or coming from the neck, or extrinsic coming from another source.
Intrinsic pain can be broken down even further, into mechanical, coming from the joint or the disc; radicular, pain from a nerve root; or myelopathic, pain from the spinal cord. The spine is composed of segments that have essentially three joints, the disc in the front and two facet joints in the back. These structures are very resistant to wear-and-tear injury for the first two decades of life but often during our twenties, these tissues start to wear out. This is called degenerative disease and is the most common reason for neck pain. Degeneration occurs simultaneously in the disc and the facet joints. This condition is progressive as we age and, by the age of 60, all of us have at least imaging (x-ray, MRI, CT scan) evidence of this process. Fortunately, it is not always symptomatic.
Degeneration of the disc has a characteristic physiologic progression. The cells within the disc and at the center of the disc make proteins crucial to the mechanical function of the disc become less active metabolically. As they become less active, they make less protein that is critical for the disc to work. This protein is responsible for imbibing water or fluid into the disc that gives the disc its mechanical strength. These proteins are also critical for the extra-cellular composition of the disc, which we call matrix. In a normal disc, the load (compression) is shared between the inner part of the disc, the nucleus, and the outer wall of the disc.
As the disc degenerates and has less fluid content, load is shifted from the center of the disc to the wall of the disc. Eventually, the outer wall of the disc can fail which would create a tear into the disc. These tears can be painful. If the disc wall is weakened enough, the disc can actually rupture or herniate. In addition, degenerative changes also occur at the facet joints. The facet joints are much like any other peripheral joint, such as the knee. They have cartilage at the ends of the bones, which collide at the joint surface. A lining tissue, called synovium, and a thick ligamentous structure called the capsule, surround the joints. These structures are very well supplied by nerves. Just as a hip or knee joint can become arthritic, so can the facet joints and thus can contribute to neck pain.
The degenerative disc is more susceptible to injury, because it is not as strong as a normal disc. However, one needs to always remember, just because a disc is degenerative, does not necessarily mean it is painful, however, it can be painful.
Pain coming from the nerve has characteristic patterns. We can break these down into two main categories. Radicular pain refers to pain coming from a nerve root. It is usually sharp, electrical type pain that goes down the upper extremity in a particular pattern. Sharp, shooting electrical type pain that goes down the extremity in a particular pattern we call dermatomes. It may be associated with numbness or weakness in the upper extremity. It can be made worse or relieved by different motion or positions of the head or neck.
Myelopathic pain refers to the symptoms coming from compression of the spinal cord. This type of pain is usually in both arms and may even go down into the legs. It is also associated with numbness or weakness in the arms and legs. In the beginning, it can be very subtle, such as just clumsiness of the hands, and progress usually slowly to where one has significant weakness of the arms and legs, eventually difficulty with gait or balance and, ultimately, loss of bowel or bladder control. This, again, takes a long time to develop in most cases. This is in contrast to mechanical or joint pain, which generally is within the neck and radiates just around the neck muscles or to the shoulder.
We can categorize different conditions of the spine based on their etiology. The mechanical nerve differentiation is more of a symptom complex. The different conditions that can cause mechanical or nerve pain are as follows. Degenerative disc disease is the most common. There is also trauma to the spine. Fractures and dislocations of the spine can cause either mechanical pain, nerve pain or both. They are usually associated with major force to the spine.
Other traumatic injuries can cause damage to the joint or disc, but do not cause an instability of the cervical spine. Direct blows to the head or neck, lifting injuries or overuse type injuries and poor postures can cause this type of injury. In addition, flexion/extension injuries, such as the "whiplash" injury to the cervical spine, are known to cause significant pain syndromes. Another category would be inflammatory conditions of the spine. This category includes rheumatoid arthritis, infection, neoplasm or tumors, congenital abnormalities of the spine, and miscellaneous conditions such as ossification of the posterior longitudinal ligament (where the ligaments themselves turn into bone thereby causing compression on the nerves), syringomyelia (a cyst within the spinal cord), and neurologic disorders (refer pain to the neck). An example of this would be multiple sclerosis.
Extrinsic conditions that can cause pain in the neck would include shoulder pathology and nerve root compression syndromes such as thoracic outlet syndrome, compression neuropathies about the elbow around the ulnar nerve or the median nerve, and carpal tunnel syndrome with compression of the median nerve at the wrist. Again, there can be neurologic diseases either coming from the brain or more generalized neurologic disorders such as peripheral neuropathies. There can also be conditions of the cardiovascular system, such as angina, or pulmonary conditions such as pulmonary tumors that can actually present in the shoulder or the neck.
Because there are so many reasons for neck pain, it is very important that the physician do a very careful history and physical exam of the cervical spine. The exam will often include the entire body, as well as the neurologic and vascular system, in order to determine exactly where the pain is coming from. In addition, the physician will usually employ the latest diagnostic imaging techniques, as well as differential injections around the neck or shoulder and upper extremity to come to a specific diagnosis. When neck pain persists, it is important to have a specific diagnosis so that treatment can be tailored to exactly what is wrong.
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