Numbness is a very common and significant symptom of a cervical disorder. However, it is a poorly understood and difficult to describe symptom. Numbness is usually caused by what is commonly called a "pinched nerve." A nerve can get "pinched" or blocked by a number of cervical disorders. This blocking of the nerve causes the flow of nutrients to the nerve's membrane to slow down. This slow down can eventually cause the membrane to lose its ability to transmit tiny electrical charges and the nerve fiber may eventually die. When enough nerves stop working, the skin may feel numbness or a muscle supplied by the nerve may not be able to function normally.
A common cause for numbness in the arms or legs, associated with back or neck pain, is a herniated disc that "pinches" a nerve where it exits the spinal column. When the outer lining (annulus) of a disc "tears," its center (the nucleus) may rupture and press a spinal nerve(s) against the bony surface of a vertebra. Another cause of numbness is degenerative disc disease. DDD can cause bone spurs to form around the nerve roots. This usually occurs inside the foramen - the opening in the cervical spine where the nerve root leaves the spine to travel into the arm. If these bone spurs get large enough, they may begin to rub on the nerve root causing irritation. This causes the same symptoms as a herniated disc. The irritation causes: pain to run down the arm, numbness to occur in the areas to which the nerve provides sensation, and weakness in the muscles that the nerve supplies.
Spinal stenosis, or the narrowing of the spinal canal is another disorder that can cause the symptom of numbness. In the late stages of spinal degeneration, bone spurs and arthritic changes can make the space available for the spinal cord, within the spinal canal, much smaller. The bone spurs may begin to press on the spinal cord or the nerve roots, and that pressure on the nerves in the spinal cord can cause numbness.