Uncommon injuries: Pec minor - a diagnostic dilemma

Isolated pec minor injuries are rare, but present a diagnostic dilemma when they do occur. Andrew Hamilton explains how clinicians can diagnose and treat these injuries in athletes.

A variety of conditions cause musculoskeletal shoulder pain which radiates to the anterior chest. These include contusions from trauma, costochondritis, pectoralis muscle strains, and tendon rupture. However, while rare in athletes, another possible cause is an isolated pectoral minor (PMi) tear.

The literature documents a limited number of such injuries, most of which tend to occur in sports as a result of direct trauma. Such sports include American football and ice hockey^(1,2,3). In an example of a non-traumatic injury, Columbia University reported the occurrence of a PMi tear in a healthy 24-year old woman as a result of performing a side-plank exercise at the gym. The likely mechanism of injury was a loss of muscular endurance and an excessive eccentric load to the pectoralis minor tendon⁽⁴⁾.

Anatomy of pectoralis minor

The PMi is a fan-shaped muscle of the shoulder girdle, originating from the external surfaces of the anterior portion of the third to fifth ribs and inserting onto the coracoid process of the scapula (see figure 1). The pectoralis minor lies beneath the pectoralis major. The pectoralis muscles together form the anterior wall of the axilla. In terms of its biomechanical function, the PMi muscle helps protract, depress, and stabilize the scapula. Therefore, it is principally used in shoulder movements of flexion, adduction, and internal rotation. In addition, the location and function of the PMi mean that when the scapula is fixed, the PMi aids respiration⁽⁵⁾.

Figure 1: Anatomy of pectoralis minor (showing relationship with pec major)

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PMi injury mechanisms

Pectoralis major tears typically occur when the shoulder is in abduction, extension, and external rotation. Weightlifters and those who play contact sports are particularly susceptible to stress from eccentric loads in this position⁽⁶⁾. By contrast, the exact mechanism of a PMi tendon rupture is poorly understood, and several factors may combine to play an important role⁽⁴⁾. These include⁽²⁾:

• Excessive strain from abnormal loading.
• Cumulative stress and trauma that exceeds the capability of the tissue to adapt to the loading.
• Chronic PMi shortening and tightness (eg as a result of poor posture or naturally occurring anatomical variations – see this article for a more in-depth discussion).
• Direct impact on the front of the shoulder.
• Forced external rotation of the arm in slight abduction, or with the arm in extension and shoulder in flexion.

Through experimental modeling, researchers agree that the myotendinous junction is the most common site of injury in PMi muscle injury⁽⁷⁾.

Diagnosis of a PMi injury

Diagnosing an isolated PMi injury is challenging for the clinician; not only is this injury often mistaken for a pectoralis major injury, but the two injuries also coexist (see table 1). Since the treatment approach to the two injuries differ the correct diagnosis of an isolated pectoralis minor tear is important and may require imaging to confirm^(1,8).

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Study	Injury mechanism	Initial diagnosis	Imaging results
Mehalloet al.(2004)	Female soccer player hit on the front of the right shoulder during a tackle. The shoulder was pushed superiorly and posteriorly. The patient’s arms were by her side at the time of impact	Grade 1 pectoralis major strain	MRI indicated edema and lack of definition of the right PMi muscle. Pectoralis major intact, including the humeral attachment
Kalra et al.(2010)	Professional ice hockey player received contact with the affected arm in slight abduction, external rotation and extension	Pectoralis major strain	MRI showed extensive edema in the PMi muscle and a complete isolated tendon tear with 2cm of retraction. Pectoralis major was intact
Li et al.(2012)	High school football player injured when making a tackle and leading with left arm and chest	No initial diagnosis	MRI showed significant edema within the PMi muscle and detachment of the tendon from the coracoid
Zvijacet al.(2009)	Two male professional football players (NFL); during practice with blocking exercises. Arm position was in extension with the shoulder in flexion in both cases	No initial diagnosis	Anteroposterior and cross-sectional MRI imaging showed isolated tear of the PMi muscle

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In the clinic, the diagnosis of an isolated PMi involves taking a detailed history, with particular attention paid to the mechanism and location of any impact. To reiterate, clinicians should take specific note of injuries caused by a direct anterior force to the shoulder, forced external rotation of the arm in slight abduction, or with the arm in extension and shoulder in flexion. A patient may also report a ‘pop’ or snapping sensation in the anterior shoulder and chest area at the time of injury. Athletes often complain of an immediate pain sensation that radiates up the neck or down the chest and arm.

Upon physical examination of the patient, there is typically tenderness upon palpation over the coracoid process, combined with a reduced range of motion. Pain and weakness are also common. Shoulder extension and external rotation generate pain. Evaluation of the shoulder at 90° and 150° of horizontal abduction creates the most tension across the pectoralis minor. Other indications of a possible PMi injury include tenderness over the bicipital groove and the pectoralis major tendon, and pain on resisted shoulder internal rotation. Active scapular protraction and retraction may also be painful; however, the brachial plexus and axilla are likely to be non-tender⁽⁴⁾.

Imaging

Due to its deep location and the fact that a PMi injury frequently occurs in conjunction with a pectoralis major injury, MRI imaging is beneficial for confirming (or refuting) a suspected PMi injury diagnosis. Computerized tomography imaging (CT scanning) may also be helpful in making the diagnosis. Different imaging modes help establish an accurate picture of the extent and nature of the injury. These include sagittal T2 fat-saturated imaging (MRI), coronal proton-density fat saturation sequence imaging (MRI), and axial CT imaging of the coracoid (see figures 2a and 2b).

Figure 2: Imaging modalities in PMi⁽⁹⁾

A: Axial CT image of the coracoid shows the pectoralis minor muscle and minimal surrounding fat stranding, indicative of a tendon tear



B: Coronal proton-density fat saturation sequence MRI demonstrates pectoralis minor peritendinous fluid and edema (red arrow)

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Treatment options

Patients with complete pectoralis major tears usually undergo surgery to regain optimal function⁽¹⁰⁾. In isolated pectoralis minor tendon tears, however, a conservative treatment approach is typically recommended. Recommend rest, ice, and anti-inflammatory medication for the first two to four weeks following the injury. The athlete may use an arm sling to increase comfort, but complete immobilization isn’t necessary. After the initial rest period, begin gentle non-resisted exercises to preserve shoulder integrity but avoid offending movements. Consider activities such as the pendulum, assisted shoulder ladder, and assisted pulley exercises within the zone of comfort.

The active rehabilitation phase for PMi tears can last up to 12 weeks. Progress neuromuscular and strength training with the athlete as tolerated (see table 2). The prognosis for shoulder function is good, with most athletes returning to pre-injury sports participation.

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Week post injury	Recommended Treatment
0	Sling and physical therapy modalities for pain and swelling.
2	Avoid passive external rotation, abduction, and scapular retraction.
3	Start active assisted and active abduction movement. Careful return to skating.
4	Cautious return to play (without pain/weakness). Begin resisted strengthening including scapular retraction/protraction as well as shoulder depression exercises.
8	Progress to pain-free push-ups.
8+	Full return to sport.

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Summary

Isolated PMi injuries are comparatively rare and challenging to diagnose. A correct diagnosis requires careful history taking to determine the mechanism of injury and a detailed physical examination. MRI imaging typically shows edema at the tendon insertion site of the pectoralis minor muscle onto the coracoid process.  The pectoralis major muscle usually remains intact. Conservative treatment approaches usually suffice and most athletes return to sport with no long-term detriment to performance.

References

1. American Journal of Orthopedics 2009; vol. 38, no. 3, pp. 145–147
2. Orthopedics 2012, vol. 35, no. 8, pp. e1272–e1275
3. Skeletal Radiology 2010; vol. 39, no. 12,pp. 1251–1253
4. Case Rep Orthop. 2019 Aug 29;2019:3605187
5. Moore KL ,Dalley AF . Clinically oriented anatomy. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2005
6. Arthroscopy Techniques 2012; vol. 1, no. 1, pp. e119–e125
7. Exercise and Sport Sciences Reviews, vol. 19, pp. 419–445, 1991
8. Clin J Sport Med 2004;14(4):245–6
9. Radiol Case Rep. 2018 Oct; 13(5): 1053–1057
10. Am J Sports Med 2010;38(8):1693–705