High-resolution ultrasound and MRI in the evaluation of pectoralis major injuries

PM tears occur almost exclusively in active men between 20–40 years of age^(1,4,13,14). Approximately 75% of these injuries are related to sports activity with weight-lifting accounting for nearly 50% of the reported cases^(3,4). PM tears often present clinically with sudden onset of pain and weakness during arm adduction^(1,14). Chest wall and axillary hematoma formation and swelling is frequently encountered and can sometimes obfuscate medial retraction of the muscle^(1,7).

The variation in muscle segment lengths in the PM is atypical compared to other muscles, which demonstrate more uniformity^(2,6). While this maximizes power production, it predisposes the inferior segments of the sternal head to higher fiber excursion during 0° and 30° of humerus extension⁽⁶⁾. Thus, the biomechanical model of failure is described as muscle overload during eccentric contraction with the humerus extended, as in performing the bench press maneuver^(1,5). As a result, the inferior sternal head fibers are most commonly torn^(2,10). The PM tendon is most commonly torn at the humeral insertion⁽¹³⁾. The myotendinous junction is the second most common location of PM tears and has been documented to occur more frequently in those older than 30 years of age⁽¹⁵⁾. With respect to tears involving the muscle proper, those involving the muscle origin from the sternal or clavicular head or intramuscular tears are less common than tears at the myotendinous junction.

The classification system developed by ElMaraghy and Deveraux is the most commonly used to describe tear of the PM and is based on the “U-shaped” orientation of the tendon (Fig. 6)⁽⁴⁾. “Width” is characterized as the craniocaudal extent of the anterior and posterior layers⁽⁴⁾. For example, a full width tear involves the entirety of the posterior or anterior layer. “Thickness” refers to the antero-posterior orientation of the fibers. A full thickness tear will therefore involve both the posterior and anterior layers. Tears are also characterized by the location: at the tendon insertion on the humerus, mid tendon substance, myotendinous junction, intra-muscular, or at the muscular origin. Tears at the humeral insertion can have associated avulsed osseous fragments; however, this is a rare injury location⁽¹³⁾.

Muscle fiber and tendon disorganization, laxity and/or focal defect are characteristic imaging findings of acute PM tear (Fig. 7, Fig. 8, Fig. 9, Fig. 10). In the acute phase, this manifests as a focal T2 hyperintense or hypo/anechoic abnormality within the substance of the muscle or tendon on MRI and US, respectively.

Hematoma formation is a secondary sign of injury and can be within the muscle or tissues surrounding the torn tendon (Fig. 7, Fig. 8).

Acute hematoma demonstrates fluid signal on MRI and is predominately hypoechoic on US⁽¹²⁾. In the subacute and chronic phases, hematoma can appear more organized and anechoic on US and, depending on chronicity, shows variable signal intensity on MRI⁽¹²⁾.

Full-thickness tears at the distal humerus insertion result in nonvisualization of PM tendon fibers superficial to the long head biceps brachii tendon which may be anteriorly displaced^(8,10) (Fig. 9). Care must be taken on image interpretation to accurately identify the anterior and posterior layers of the PM tendon so that full width partial thickness tears are not misdiagnosed as completely intact tendon (Fig. 10).

Periosteal reaction can be detected on US in the setting of PM tendon injury (Fig. 10 D). MRI offers the additional benefit of detecting bone marrow edema which can be a secondary sign of injury (Fig. 11)⁽¹⁰⁾. Radiography is beneficial in detecting periosteal reaction and osseous avulsion fracture (Fig. 12).

Findings of chronic PM injury include scar tissue formation, muscle atrophy, and tendon retraction (Fig. 13). A relative paucity of edema surrounding the PM tear is another characteristic of chronic injury.

PM strain manifests as less well-defined echogenicity and architecture on US and feathery fluid signal MRI abnormality without overt tear (Fig. 14).

In most instances, clinical history, patient demographics, and physical examination are adequate to diagnose the anterior chest wall findings as traumatic in etiology. However, infection and neoplasm are also possible and can present with similar symptoms and imaging findings. For example, a posttraumatic hematoma can appear similar to the more focal, circumscribed, or “mass-like” appearance of abscess or neoplasm (Fig. 15). This is particularly true for chronic PM tears, where the fiber disorganization may be less obvious with decreased edema and the propensity for chronic hematomas to have thicker walls. On post-contrast MRI, fibrous or scar tissue can enhance which may complicate the diagnosis. Axillary lymphadenopathy is rare in isolated traumatic muscle injury and if present, it should raise concern for infection or neoplasm.

Non-operative management of PM tears is recommended for partial tears, tears that exclusively involve the muscle belly, and contusion or strain. Initial management consists of rest, ice, analgesia, and immobilization of the adducted and internally rotated arm in a sling. Patients transition from passive to active range of motion and eventually to full resistance training from two weeks to four months post injury⁽¹⁶⁾. Return to contact sports should not commence until 5–6 months after injury and, in some instances, certain training maneuvers like the bench press should be permanently avoided⁽¹⁶⁾. Often, patients experience strength deficit and cosmetic defect with non-operative management^(9,17). In the setting of low functional demand, patients with full-thickness tears may also undergo nonoperative management with satisfactory recovery to performing activities of daily living⁽¹⁸⁾.

In 1980, Tietjen described a classification system for the management of PM injury based upon tear location and severity⁽¹⁹⁾. This system was modified by Bak et al. to include further subclassification of injury location⁽³⁾ (Tab. 1). Operative management is recommended for tears at the humeral insertion and for musculotendinous junction tears with severe cosmetic/functional deformity (Fig. 16). The indications for surgical intervention have been further expanded to complete intra-tendinous tears and those located at the sternal head/posterior lamina^(1,20).

Fig. 16.

It is generally accepted that surgical repair produces higher patient satisfaction with better functional and cosmetic outcomes^{(1,3,6,9,17,21)}. Bone trough, suture anchor, and cortical button technique are all effective methods to repair the PM tendon^(13,22–24). Further description of these techniques is beyond the scope of this article.

Patients are immobilized in a sling for six weeks following surgery. Passive range of motion begins after six weeks and at three months the patient should have full range of motion and can begin light resistance training⁽²⁰⁾. Return to full activity is achieved at six months postoperatively⁽¹⁷⁾. High-weight, low repetition exercises that involve the PM, such as bench press, are discouraged indefinitely⁽²⁰⁾.

The timing of surgical intervention is important. Repair of an acute PM tear leads to better patient satisfaction and functional outcomes^(3,25,26). After 6 weeks, a PM tear is generally considered to be chronic. Surgical management of chronic injuries can be more technically challenging and often requires a larger surgical field secondary to scar tissue formation and muscle retraction⁽⁴⁾.

Artifact from surgical intervention and hardware is commonly visualized on post-operative MRI and US, (Fig. 10 A and Fig. 17).

Fig. 17.