The pectoralis major muscle contains two recognizable heads; the clavicular head and the costosternal head. The clavicular head emerges from the medial clavicle and the upper sternum while the costosternal head on the sternum emerges from the aponeurosis of the external oblique and the first six costal cartilages of the rib cage. They both combine to form the anterior wall and fold of the axilla, extending across the shoulder and inserting onto the proximal humerus.
The clavicular and upper sternal portion of the muscle precisely inserts on the humerus below the insertion of the lower sternal and external oblique fibres. Each different tendon divides onto each other approximately 90 to 180 degrees before being introduced on the humerus. Over a study utilizing fine wire gauges, research determined that the sternocostal head and its tendon stretch unevenly in the last 30 degrees of humeral extension in comparison with the clavicular head. Because of this, the sternocostal head has a higher risk of injury and rupture as it is most exposed to intense stretches. In addition, this also shows that partial ruptures of the tendon are more common than the complete rupture of both heads.
The pectoralis major is a powerful internal rotator, adductor and flexor of the shoulder. It functions to stabilize the shoulder in contact sport conditions. Researchers demonstrated, however, that the pectoralis major is not as essential towards normal shoulder function as other shoulder muscles. It is necessary though for strenuous physical activities which indicates that some athletes may require surgical repair while others may respond well to conservative treatments.
Injuries to the pectoralis major include contusions or sprains, partial tears, complete tears, muscle origin tears, muscle belly tears or the development of musculotendinous junction, or MTJ. Most frequently, ruptures of both heads are not seen where only the inferior fibres of the sternocostal head has ruptured, giving an incorrect perception that the entire tendon still remains intact. Complete ruptures almost always include an avulsion of the humeral enthuses.
Pectoralis major ruptures are moderately uncommon types of sports injuries. These generally occur specifically on contact, caused by a sudden contraction of the muscle, usually with particular stretching positions, such as during the bottom of a bench press or during tackling in rugby or football. These injuries have become more common with the increasing popularity of contact sports. For more information, please feel free to ask Dr. Jimenez or contact us at (915) 850-0900.