The Clinical Syndrome

As its name implies, the supinator muscle supinates the forearm. Curving around the upper third of the radius, the supinator muscle is composed of a superficial and a deep layer. The superficial layer originates in a tendinous insertion from the lateral epicondyle of the humerus, the radial collateral ligament of the elbow, and the annular ligament of the supinator crest of the ulna.

The supinator muscle is susceptible to the development of myofascial pain syndrome. This pain is most often the result of repetitive microtrauma to the muscle caused by such activities as turning a screwdriver, prolonged ironing, handshaking, or digging with a trowel ( Fig. 43.1 ). Tennis injuries caused by an improper one-handed backhand technique have also been implicated as an inciting factor in myofascial pain syndrome, as has blunt trauma to the muscle.

Supinator syndrome is usually the result of repetitive microtrauma caused by activities such as turning a screwdriver, prolonged ironing, handshaking, or digging.

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 are generally localized to the part of the body affected, the pain is often referred to other areas. This referred pain may be misdiagnosed or attributed to other organ systems, thus leading to extensive evaluation and ineffective treatment. Patients with myofascial pain syndrome involving the supinator muscle often have referred pain in the ipsilateral forearm.

The trigger point is pathognomonic of myofascial pain syndrome and is characterized by a local point of exquisite tenderness in the affected muscle. Mechanical stimulation of the trigger point by palpation or stretching produces not only intense local pain but also referred pain. In addition, an involuntary withdrawal of the stimulated muscle, called a jump sign, is often seen and is characteristic of myofascial pain syndrome. Patients with supinator syndrome have a trigger point over the superior portion of the muscle ( Fig. 43.2 ).

Patients with supinator syndrome have a trigger point over the superior portion of the muscle.

(From Waldman SD. Atlas of pain management injection techniques. 2nd ed. Philadelphia: Saunders; 2007:155.)

Taut bands of muscle fibers are often identified when myofascial trigger points are palpated. Despite this consistent physical finding, the pathophysiology of the myofascial trigger point remains elusive, although trigger points are believed to result from microtrauma to the affected muscle. This trauma may result from a single injury, repetitive microtrauma, or chronic deconditioning of the agonist and antagonist muscle unit.

In addition to muscle trauma, various other factors seem to predispose patients to develop myofascial pain syndrome. For instance, a weekend athlete who subjects his or her body to unaccustomed physical activity may develop myofascial pain syndrome. Poor posture while sitting at a computer or while watching television has also been implicated as a predisposing factor. Previous injuries may result in abnormal muscle function and lead to the development of myofascial pain syndrome. All 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 supinator muscle seems to be particularly susceptible to stress-induced myofascial pain syndrome.

Stiffness and fatigue often coexist with pain, and they increase the functional disability associated with this disease and complicate 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, and management of these psychological disorders is an integral part of any successful treatment plan.