Clinical History: A 26 year-old male was injured while bench-pressing. (1a) Coronal oblique T2-weighted fat-suppressed and (1b) axial proton density-weighted fat-suppressed images are provided. What are the findings” What is your diagnosis?
Musculotendinous rupture of the sternal head and strain of the clavicular head of the pectoralis major muscle (pectoralis tear).
Rupture of the pectoralis major muscle is a once rare injury that is becoming more common due to increasing numbers of intense weight-training and high-performance athletes. While the diagnosis is usually suspected clinically, assessment of the extent and location of the injury is often limited in the acute setting. With an understanding of the complicated anatomy of the pectoralis major musculotendinous unit, MRI provides the anatomic detail necessary to allow accurate localization and characterization of pectoralis major musculotendinous injuries.
Anatomy and Function
The pectoralis major muscle is a fan shaped muscle with 3 heads originating from clavicular, sternal and abdominal origins. The clavicular head takes origin from the medial one half to two thirds of the clavicle. The upper portion of the sternal head arises from the manubrium and upper body of the sternum and ribs.2-4 The lower portion of the sternal head arises from the distal body of the sternum and ribs.5-6 The abdominal head arises from the external oblique muscle fascia.1 Although indistinguishable by MR, the pectoralis tendon is composed of two laminae: the clavicular lamina and the sternal lamina. The clavicular lamina is composed of fibers from the clavicular head and the upper sternal head fibers with the tendon fibers arising from the clavicular head being most superficial. The distal inserting fibers of the clavicular lamina blend with the distal deltoid inserting fibers. The sternal lamina is composed of the lower sternal and abdominal heads and insert deep and proximal to the clavicular lamina, contributing to the long biceps tendon sheath. The fibers from the abdominal head undergo a 180-degree rotation before inserting on the humerus. Thus the tendon fibers from the abdominal head are most superior in their insertion onto the lateral aspect of the bicipital groove (4a).2
The multiple muscle head origins and crossing pattern of insertion allow the pectoralis major muscle to exert a wide range of actions on the humerus. Depending on the position of the humerus, the pectoralis major muscle can adduct, flex, and internally rotate the humerus against a stable thorax. Against a fixed humerus, the pectoralis muscle acts as a climbing muscle, pulling the thorax upward. It is also an accessory muscle of respiration when the shoulders are fixed in an elevated position.
Normal MRI Anatomy
The pectoralis tendon is best seen on axial T1 and T2-weighted images as a curvilinear low-signal band inserting onto the lateral ridge of the bicipital groove of the humerus. The superior-most inserting fibers can be identified curving anterior to the biceps tendon at the approximate level of the quadrilateral space (5a).3 The tendon length is variable ranging from 5 to 15 mm and the fibers insert over a cephalocaudal distance of 4-6 cm. The distal extent of tendon insertion is typically seen just proximal to the deltoid tubercle.3 The pectoralis major muscle is the most superficial muscle group along the superior chest wall, separated from the anterior deltoid by the deltopectoral groove, which contains the cephalic vein.
Injury Mechanism and Physical Examination
Injury of the pectoralis major tendon or musculotendinous junction most commonly occurs when the muscle is under extreme tension with application of additional forceful stretching. These injuries are most often encountered in weight lifters, with the injury occurring almost exclusively during bench-press exercise. Pectoralis major tendon injuries are also seen in football, waterskiing, and wrestling.
The patient typically presents after experiencing a “pop” following excessive muscle tension or after a direct blow to the shoulder while the arm is in abduction and extension. Ecchymosis and swelling are seen in the axilla and upper arm with asymmetry of the pectoralis musculature. In the acute setting, marked edema, pain, and decreased range of motion may hinder the clinical assessment of the extent and location of the injury.
MRI offers multiplanar imaging and fluid sensitive sequences that are ideal for evaluating acute pectoralis major muscle and tendon injuries. Fluid sensitive sequences are valuable for detecting the site of injury, demonstrating edema and hemorrhage in the muscle, tendon and in the surrounding soft tissues. The multiplanar capabilities of MRI allow optimal depiction of the portions of the pectoralis major muscle and tendon involved.
Incomplete ruptures of the pectoralis major are most common and typically occur at the musculotendinous junction or muscle belly of the sternal head.4 Edema and hemorrhage are seen at the site of the musculotendinous tear. The muscle may be retracted, but the inserting pectoralis major tendon fibers remain intact without associated hemorrhage or edema (6a).
Complete ruptures occur most commonly at the distal tendon or its insertion.5 Hemorrhage and edema are seen anterior to the humerus without visualization of the inserting pectoralis major tendon fibers. The biceps tendon may be slightly displaced from its normal location anterior to the humerus because of associated biceps sheath injury and periosteal hemorrhage and edema (7a).
In patients with pectoralis major ruptures, coronal oblique images along the plane of the muscle and tendon are helpful in establishing which portions of the pectoralis major muscle are involved (8a).
Isolated pectoralis major intramuscular tears may be seen as a result of a bench-press injury, but they more frequently occur from a direct blow to the muscle. Intramuscular increased signal on fluid sensitive sequences easily confirms this injury, and is effective in evaluating its extent (9a).
Treatment of acute pectoralis major ruptures varies depending on the patient’s level of activity. Non-operative treatment is advocated for complete tears in inactive or older patients, and small partial tears. For complete ruptures or high-grade partial tears in younger, more active patients, early surgical repair has been shown to provide a better outcome than delayed repair. Early surgical repair lessens the occurrence of adhesions, shortens the time to functional recovery and improves the cosmetic result. Although not preferred, repair of chronic tears is associated with a superior functional outcome than conservative management.6
Rupture of the pectoralis major musculotendinous unit, though rare, is being seen with greater frequency in certain sports and in high-intensity athletic training. Because early detection and surgery is associated with a more favorable functional and cosmetic result, accurate assessment of the extent and location of injury is important. Physical examination may be unreliable in the acute setting because of swelling, pain and spasm. MRI enables accurate diagnosis of injuries to the pectoralis muscle and tendon, thus allowing improved treatment planning and outcomes.
1 Jobe C. Gross Anatomy of the Shoulder. In: Rockwood C, Masten F, eds. The Shoulder 2nd edition. Philadelphia, PA: W.B. Saunders,1998; 34-97.
2 Connell DA, Potter HG, Sherman MF, Wickiewicz TL. Injuries of the pectoralis major muscle: evaluation with MR imaging. Radiology 1999;210:785-791.
3 Lee J, Brookenthal K, Ramsey M, Kneeland J, Herzog R. MR Imaging Assessment of the Pectoralis Major Myotendinoud Unit: An MR Imaging-Anatomic Correlative Study with Surgical Correlation. AJR 2000;174:1371-1375.
4 Park J, Espiniella J. Rupture of pectoralis major muscle: a case report and review of the literature. J Bone Joint Surg (Am) 1970;52:577-581.
5 McEntire J, Hess W, Coleman SS. Rupture of the pectoralis major muscle: a report of eleven injuries and review of fifty-six. J Bone Joint Surg (Am) 1972;54:1040-1046.
6 Aarimaa V, Rantanen J, Heikkila J, Helttula I, Orava S. Rupture of the Pectoralis Major Muscle. AJSM 2004; 32:1256-1262.