Understanding Pain

What Causes Pain?

When an accident causes an injury, pain is often the first noticeable sensation. Although pain can be very acute at the onset and gradually ease, it may nonetheless linger for a long period of time. Some neck and back injuries are not only associated with localized pain, but also symptoms of numbness, radiculopathy, tingling, weakness and/or impaired mobility.

These symptoms can be frustrating and severely impair the overall quality of a person’s life. To understand pain and its associated symptoms, you must have an understanding of the body’s central and peripheral nervous systems.

Central and Peripheral Nervous Systems

The human body has a complex network of nerves that control both movement and sensation. There are two components to this network: the central and peripheral nervous systems. The central nervous system solely refers to the brain and spinal cord, which are protected by the skull and vertebrae of the spine. The peripheral nervous system consists of all the nerves that connect the spinal cord to the rest of the body.

At each vertebrae, there are two nerve roots that exit each side of the spinal cord. These roots are bundled together into a structure called an axion which divides and connects the two nerves that supply the bones, muscles, and skin at that vertebral segment. This segment is called a dermatome.

What is a Dermatome?

Dermatomes are essentially a peripheral nerve map. There are 31 total dermatomes, including those corresponding to the 24 vertebrae plus the nerve roots that extend from the sacrum or “tail bone”. Any sensation of pain or numbness is produced by the nerves of the affected dermatome.

For example, the nerve roots at the seventh cervical vertebrae control the peripheral nerves of the neck, shoulders, and outer arms. Those of the 12th thoracic vertebrae control the lower half of the arms, the chest, mid-back and abdomen. The lumbosacral dermatomes include the nerves of the lower back, groin, buttocks, legs and feet.

Examples of injuries that affect specific dermatomes are:

• Pain or numbness of the arms from whiplash during a car accident;
• “Shooting” pain down the back of the leg from a lumbar herniated disc, a condition known as radiculopathy;
• Pain with walking after a “sitting down” fall;
• Toe numbness from a lumbosacral herniated disc.

Essentially, any fracture, sprain, disc injury, or laceration triggers the nerves of that dermatome to produce pain. Other types of peripheral nerves control the organs of the body, but they differ from those that control the bones, muscles and skin.

Isolated Nerve Injuries

When a single dermatome is affected, it corresponds to a specific nerve root. For example, an impinged right cervical nerve root causes radiculopathy, pain or numbness in the right arm. This arm may seem weaker than the left arm, and, in severe cases, can have atrophy of the muscle. This is called radiculopathy.

Mid-back radiculopathy, or thoracic radiculopathy, can cause pain with coughing or sneezing, but walking may be impaired when a lumbar dermatome is affected. Low back, or sacral radiculopathy, can lead to incontinence, or difficulty using the bathroom. This can be caused by an intervertebral disc herniating onto a nerve root. One analogy is a home electrical panel of circuit breakers, when one breaker is turned off, the power is cut in the associated room but remains on everywhere else in the house.

Diagnosis

Evaluation of these injuries should involve a multi-disciplinary approach. In addition to an examination by a primary care physician, the expertise of a neurologist or an orthopedist is usually necessary. The orthopedist can evaluate the vertebral bones and intervertebral discs via imaging studies such as x-rays, CT scans and Magnetic Resonance Imaging or MRI.

These studies are helpful in locating the source of nerve root compression. Alternatively, an neurologist may order electro diagnostic testing. These include nerve conduction studies (NCV) and electromyography (EMG). The EMG measures the power to muscles, or their innervation, and is helpful in cases of muscle weakness and atrophy.

Nerve conduction studies test the speed at which signals travel along neves, and help to determine the cause of localized numbness, tingling, and pain. Unlike EMG, this test is non-invasive. Electrodes are placed on the skin during nerve conduction studies, and there is minimal discomfort.

Treatment Options

Although surgery may be necessary for some neck and back injuries, a variety of non-surgical options are usually considered first. Pain may initially be managed with medications such as non-steroidal anti-inflammatories, muscle relaxants, and topical lidocaine. Opiod medications are prescribed only for a limited number of weeks due to their habit forming potential.

Physical therapy can assist with pain reduction, improving mobility, and maintaining muscle strength. Local steroid injections, that can be administered by a pain management doctor, can also provide temporary relief when other modalities are ineffective. Neck immobilization or traction is used until swelling has resolved, and can reduce the need for more aggressive treatments.

If, after up to eight weeks of treatment, there is no improvement, surgery may be recommended. There are generally two options: minimally invasive techniques and open back surgery. In either procedure, the damaged intervertebral disc portion or bone is “trimmed” or removed depending on the extent of nerve impingement. Minimally invasive options can reduce the surgery’s duration as well as a patient’s time to recover.

The prognosis for recovery after surgery varies by type and severity of the injury. Most cases of cervical radiculopathy respond well to non-surgical treatment when intervention occurs early. Thoracic radiculopathy is rare, but most patients have good treatment outcomes as well. For lumbosacral nerve compression, the prognosis varies and may require chronic care.