The final ingredient in chronic neck pain is the motor systems. To explain this we first need to review the two major functions of muscle groups. The first is to stabilize joints and the second is to move joints. When either of these functions go wrong it can increase the likelihood of chronic pain.
When we use our muscles to move at a joint, we have to fire other muscles to hold the joint together so that we don’t dislocate or damage anything. In the neck, these stabilizing muscles are under automatic control and fire automatically when muscles that move the joint fire. These stabilizing muscles are very small and are the deepest muscles in the neck, closest to the spine. Some of them rotate the vertebrae, some cause them to tip to the side and others cause them to tip forward and backward. They fire to counteract the force of the muscle doing the moving and are called intrinsic muscles. For a demonstration of how we cannot control these muscles voluntarily, try sitting still while you rotate just one single vertebra in your spine. You can’t do it. They only fire along with larger muscles.
The actual movement of the neck is accomplished by larger muscles that we call prime movers. They include the trapezius, the scalenes and the splenius (among others). These muscles span several joints and pull the neck into different positions, allowing us to rotate our head, lean to the side, look up, and look down. We can control these. In an emergency these muscles can fire to stabilize a joint in the neck, but when that happens it is usually accompanied by pain and stiffness and we call it a muscle spasm.
Now that we know what the muscles do, let’s discuss how their malfunction can create chronic pain. There are two mechanisms that cause chronic pain to develop: one is using the prime movers for stabilization, and the second is using the wrong muscles when you want to move a joint.
One of the requirements for muscle health is muscle use. A muscle that does not fire will lose half its strength every 7-10 days. If you injure your neck and then have restricted movement for any period of time you start losing the strength in the muscles associated with that movement, both the intrinsic muscles as well as the larger prime movers.
The spine is made of individual segments called vertebra. The stabilizing muscles run from one vertebra to the next. If because of injury, overuse, bad posture we lose movement in a segment, it causes a painful experience. Until motion is regained the small intrinsic stabilizing muscles between the vertebra do not fire. Within a week these muscles have lost one half of their strength; within two weeks the strength is down to twenty five per cent of normal. Now, if motion is regained, the pain is alleviated but the joint is not stable and fails when a load is put on the neck. This can cause recurrent pain. This situation is best addressed with manipulation to restore movement and resolve the pain, followed immediately by isometric stabilization to start firing the stabilizing muscles and rebuilding their strength and activation.
The second cause of muscle-related pain is substitution of large prime movers for smaller intrinsic stabilizing muscles. When the small muscles don’t do their job, the brain will use the large muscles to try to stabilize the joint. When this occurs it creates pain and causes muscle spasm in the large muscle. In addition, when it hurts to move we develop patterns of movement and muscle activity that are inefficient. For example, if it hurts to reach the arm out from the shoulder, people will frequently use neck muscles to lift the shoulder. Even after the injury is better, they keep using the neck to move the shoulder, which puts chronic strain on the neck. This is called abnormal recruitment of muscles and must be addressed if the neck is to be truly stable.
An important part of preventing neck pain from becoming chronic is not just to treat the pain but to also rehabilitate the small muscles of the neck, rehabilitate the prime movers, and retrain the patterns of movement.