Page 30 - Journal of Special Operations Medicine - Fall 2016

Figure 1 Magnetic resonance (MRI) image of rupture in the left pectoralis major. (A) Axial, (B) coronal, and (C) sagittal fat-
saturated blade T2 MRI (white arrows highlight injury).

(A) (B) (C)

It is composed of two main divisions: the clavicular Imaging
head and the sternal head. The clavicular head origi- History and physical examination can generally diagnose
nates from the medial clavicle and superior sternum. a pectoralis major tear; however, imaging can be useful in
The sternal head originates from the inferior sternum, cases of uncertainty. Radiographs are commonly normal,
external oblique fascia, and the costal cartilage down although they will demonstrate any associated fractures
to approximately the sixth rib. The muscle fibers of the or tendinous avulsions. Loss of the pectoral shadow can
two heads converge as they travel laterally and rotate also be an indication of pectoralis major injury. 2–4,6 Ultra-
on each other before attaching at their insertion on the sound can be used as an adjunct to radiographs. Pecto-
humerus, lateral to the bicipital groove. The fibers of ralis major injury will present on ultrasound imaging as
the clavicular head attach anterior-inferiorly in relation uneven echogenicity and muscle thinning, compared with
to the sternal head fibers, which attach deep and more the opposite side. 2–4
superior on the humerus. Innervation is provided by
1–4
the medial and lateral pectoral nerves, which branch off MRI is considered the imaging study of choice for di-
from the medial and lateral cords of the brachial plexus. agnosis of pectorals major tears. MRI can discern the
The main blood supply comes from the pectoral branch location of injury, from muscle origin to tendinous in-
of the thoracoacromial artery. Vascular contributions sertion, along with the severity. T2-weighted imaging
also derive from the clavicular branch of the thoracoac- is most effective in identifying acute and subacute inju-
romial artery and the internal mammary artery. 3,4 ries, whereas T1-weighted sequences are more useful in
chronic cases. This information can be very helpful in
3,4
Clinical Presentation surgical planning and MRI results correlate well with
Injuries involving the pectoralis major are relatively un- findings in the operating room. 3,8
common. Approximately 200 cases have been described
in the literature, with the majority of those illustrated in Classification
the past 40 years. This injury is mainly encountered in A classification system for pectoralis major injuries,
5
men, aged 20–40 years, who were performing athletic ac- based on extent of injury and anatomic location, was
tivities. They most frequently occur during weight-lifting proposed by Tietjen in 1980 (Table 1). Grade I injuries
3,4
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exercises that cause eccentric muscle contraction (i.e., mus- are muscular contusions or tendinous sprains. Grade II
cle contraction against an overbearing force, resulting in injuries constitute partial ruptures or tears. Grade III
muscle lengthening)—specifically, the bench press. Other injuries are complete ruptures or tears, and are further
1–9
mechanisms for this injury can include forceful abduction subdivided by anatomic location. Grade IIIA complete
and external rotation of the arm. 2,10 Use of anabolic ste- injuries occur at the muscle origin. Grade IIIB injuries
roids has been found to correlate with injury as well. 2–6,9,11 occur in the muscle belly. Grade IIIC are located at the
musculotendinous junction and Grade IIID at the ten-
At the time of injury, patients may feel a tearing sensa- don, to include avulsion from the humerus. Other,
12
tion with or without an audible pop, along with pain, more simplistic classifications of injury include partial
weakness, and/or deformity of the affected muscle. Ec- versus complete, distal versus proximal, or those involv-
chymosis and swelling may develop involving the an- ing the sternal head, clavicular head, or both. 3
terior axilla, chest wall, or arm. Arm abduction may
reveal an asymmetric webbing of the anterior axillary Management
fold, compared with the unaffected side. Chest defor- Grade I injuries are treated conservatively with rest and
mity may also be accentuated with contracted arm ad- gradual return to activity. Partial tears (grade II) and com-
duction. Pain and weakness may be elicited with arm plete tears involving the muscle origin and belly (grade
adduction, internal rotation, and/or forward flexion. 3,4,7 IIIA, IIIB) are generally treated nonoperatively with sling

12 Journal of Special Operations Medicine Volume 15, Edition 3/Fall 2016