The answer is none of the above, although if you ask most people who have gone to various doctors in search of relief of their shoulder pain (especially those who have not found relief), chances are they have been given one or more of these "itis" diagnoses.
The infraspinatus muscle is a very important external rotator of the shoulder.1 It is easily overstressed; and when it develops a TP which becomes active, it can refer pain most commonly to the anterior aspect of the shoulder,2 which the patient many times describes as deep inside the joint. It can also cause pain to refer down the anterior aspect of the upper arm and the lateral forearm to the hand, and frequently refers pain to the medial border of the scapula and the suboccipital area (a commonly overlooked cause of occipital headache). The pain is usually most severe at rest, often awakening the patient from sleep. This is a common feature of myofascial pain syndromes and is probably due to decreased circulation in the muscles in general.3
Shoulder pain as caused by infraspinatus TP is especially commonly seen in athletes. In athletes who throw, the muscle can be overstrained by the repeated eccentric contraction of the infraspinatus during deceleration of the limb in the follow through phase of throwing.4 This is particularly seen in throwing athletes who are inadequately trained for this function, and who do not undergo proper warm-up or cool-down activities. In powerlifters and bodybuilders, imbalances easily develop between the internal rotators (the pectoralis major and latissimus dorsi in particular -- the "big guns" in these athletes), and the external rotators (infraspinatus and teres minor). This imbalance in activity can cause undue strain on the infraspinatus, setting it up for TP development.
Round-shoulderedness can be a predisposition for infraspinatus TPs. In the normal standing posture, the superior joint capsule of the glenohumeral joint is taut and is able to maintain the head of the humerus against the upward-facing glenoid fossa with some assistance from the supraspinatus and posterior fibers of the deltoid.6 When the shoulders become rounded, the glenoid turns downward and anterior, slackening the superior capsule. This forces the infraspinatus to act as a stabilizer of the humerus, a function to which it is not accustomed.5
Shoulder pain is very common in people of all ages and walks of life. As is the case with may neuromusculoskeletal disorders, the chiropractic physician who is trained to fully analyze the function of the locomotor system as a whole, including the myofascial system, is the practitioner who is best qualified to diagnose and treat this problem.
- Lehmkuhl, L.D.; Smith, L.K. Brunnstrom's Clinical Kinesiology, 4th ed. 1983; F.A. Davis, Philadelphia: 255.
- Travel, J.G.; Simons,D.G. Myofascial Pain and Dysfunction: The Trigger Point Manual 1983; Williams and Wilkens, Baltimore: 378.
- Lowe,J.C. The Purpose and Practice of Myofascial Therapy 1989; (Audio Cassette Album) McDowell, Houston.
- Braatz, J.H.; Gogia, P.P. "The mechanics of pitching." J Orthop Sports Phys Ther 1987; 5:56-69.
- Kessler, R.M.; Hertling D. Management of Common Musculoskeletal Disorders, 2nd ed. 1991; Harper and Row, Philadelphia: 177.
- Basmajian, J.V.; DeLuca, C.J. Muscles Alive: Their Functions Revealed Through Electromyography 5th ed. 1985; Williams and Wilkens, Baltimore: 273.
Donald R. Murphy, D.C.
Westerly, Rhode Island
Dr. Donald R. Murphy graduated from New York Chiropractic College in 1988 and thereafter obtained three years of postgraduate education in neurology. He is the clinical director of the Rhode Island Spine Center in Pawtucket, R.I., as well as clinical assistant professor at the Alpert Medical School of Brown University. He maintains a busy primary spine care practice and lectures worldwide on various topics related to spinal disorders. Dr. Murphy also serves as president of the West Hartford Group.