Injection Technique for Serratus Anterior Muscle Syndrome

Indications and Clinical Considerations

The serratus anterior muscle is susceptible to developing myofascial pain syndrome. Such pain most often occurs as a result of repetitive microtrauma to the muscle from activities such as vigorous or prolonged coughing, repetitive lifting of heavy weights overhead, and long-distance running. Blunt trauma to the muscle may also incite serratus anterior myofascial pain syndrome.

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 often is misdiagnosed or attributed to other organ systems, leading to extensive evaluations and ineffective treatment. Patients with myofascial pain syndrome involving the serratus anterior often have primary pain overlying the fifth to seventh ribs in the midaxillary line. The pain of serratus anterior myofascial pain syndrome is referred to the posterior chest wall and may radiate down the ipsilateral upper extremity into the palmar aspect of the ring and little fingers.

The trigger point is the pathognomonic lesion of myofascial pain and is thought to result from 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, there often is an involuntary withdrawal of the stimulated muscle, called a “jump sign.” This jump sign is also characteristic of myofascial pain syndrome. Patients with serratus anterior syndrome will exhibit a trigger point in the superficial muscle overlying the fifth to seventh ribs in the midaxillary line ( Fig. 106.1 ).

Taut bands of muscle fibers often are identified when myofascial trigger points are palpated. In spite of this consistent physical finding in patients who suffer from 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 the result of microtrauma to the affected muscle. This microtrauma may occur as a single injury to the affected muscle or may occur 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 develop myofascial pain syndrome. The weekend athlete who subjects his or her body to unaccustomed physical activity often may develop myofascial pain syndrome. Poor posture while sitting at a computer keyboard or while watching television has also been implicated as a predisposing factor to the development of myofascial pain syndrome. Previous injuries may result in abnormal muscle function and predispose the patient to the subsequent development of myofascial pain syndrome. All of these predisposing factors may be intensified if the patient also suffers from poor nutritional status or coexisting psychological or behavioral abnormalities, including chronic stress and depression. The serratus anterior 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 may occur 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 abnormalities must be an integral part of any successful treatment plan for myofascial pain syndrome.