Indications and Clinical Considerations
The muscles of the posterior neck are particularly susceptible to the development of myofascial pain syndrome. Flexion–extension injuries to the neck or repeated microtrauma secondary to pressure from purse straps, backpacks, or laptop computer cases may result in the development of myofascial pain in the trapezius.
Myofascial pain syndrome is a chronic pain syndrome that affects a focal or regional portion of the body. The sine qua non of myofascial pain syndrome is the finding of myofascial trigger points on physical examination. Although these trigger points generally are localized to the regional part of the body affected, the pain of myofascial pain syndrome often is referred to other anatomic areas. This referred pain may be misdiagnosed or attributed to other organ systems, leading to extensive evaluations and ineffective treatment. Patients with myofascial pain syndrome involving the trapezius frequently have referred pain into the neck, mastoid region, angle of the jaw, and upper extremity—the last leading the patient to believe he or she is having a heart attack.
The trigger point is the pathognomonic lesion of myofascial pain and is thought to be the result of microtrauma to the affected muscles. This pathologic lesion is characterized by a local point of exquisite tenderness in affected muscle. Mechanical stimulation of the trigger point by palpation or stretching produces not only intense local pain but also referred pain. In addition to this local and referred pain, often there is an involuntary withdrawal of the stimulated muscle, called a “jump sign.” This sign is also characteristic of myofascial pain syndrome.
Taut bands of muscle fibers often are identified when myofascial trigger points are palpated. In spite of this consistent physical finding in patients with myofascial pain syndrome, the pathophysiology of the myofascial trigger point remains elusive, although many theories have been advanced. Common to all of these theories is the belief that trigger points are a result of microtrauma to the affected muscle. This microtrauma may occur as the result of a single injury to the affected muscle or as the result of repetitive microtrauma or chronic deconditioning of the agonist and antagonist muscle unit.
In addition to muscle trauma, a variety of other factors seem to predispose the patient to the development of myofascial pain syndrome. The weekend athlete who subjects his or her body to unaccustomed physical activity may develop myofascial pain syndrome. Poor posture while sitting at a computer keyboard or while watching television also has been implicated as a predisposing factor to the development of myofascial pain syndrome. Previous injuries may result in abnormal muscle function and predispose to the subsequent development of myofascial pain syndrome. All of these predisposing factors may be intensified if the patient also has poor nutritional status or coexisting psychological or behavioral abnormalities, including chronic stress and depression. The trapezius muscle seems to be particularly susceptible to stress-induced myofascial pain syndrome.
Stiffness and fatigue often coexist with the pain of myofascial pain syndrome, increasing the functional disability associated with this disease and complicating its treatment. Myofascial pain syndrome may occur as a primary disease state or in conjunction with other painful conditions, including radiculopathy and chronic regional pain syndromes. Psychological or behavioral abnormalities including depression frequently coexist with the muscle abnormalities associated with myofascial pain syndrome. Treatment of these psychological and behavioral abnormalities must be an integral part of any successful treatment plan for myofascial pain syndrome.
Clinically Relevant Anatomy
The muscles of the neck work together as a functional unit to stabilize and allow coordinated movement of the head and associated sense organs. Trauma to an individual muscle can result in dysfunction of the entire functional unit. The trapezius is a primary extensor of the neck as well as part of the group of muscles known as the axioscapular group , which is involved in stabilization and movement of the scapula ( Figure 18-1 ). The upper trapezius originates at the ligamentum nuchae and the spinous processes of the cervical and upper thoracic spine and attaches to the upper margin of the scapula. The middle portion of the trapezius originates from the spinous processes of the upper thoracic spine and attaches to the medial border of the scapula. The lower fibers of the trapezius originate from the spinous processes of the lower thoracic spine and attach to the medial portion of the scapular spine. These points of origin of the trapezius and attachments are particularly susceptible to trauma and the subsequent development of myofascial trigger points (see Figure 18-1 ). Injection of these trigger points serves as both a diagnostic and a therapeutic maneuver.