Anatomy
The pectoralis major muscle is a fanshaped muscle with three origins (clavicular,
sternal and abdominal) separated by a distinct interval.
-The clavicular head forms the anterior lamina of the tendonand arises from the anterior surface of the medial two thirds of the clavicle and upper sternum.
- The sternal head comprises the manubrial head (middle lamina) arising from the mid portion of the sternum and the first-to-fifth costal cartilages.
-The abdominal head (posterior lamina) arises from the fifth and sixth ribs and the fasciae of the external oblique and transversus abdominis
muscles .
The muscle fibers converge into three laminae and twist 180° coalescing into a single tendon to insert at the lateral lip of the intertubercular groove,
crossing over the biceps tendon. As a result of the 180°twist,
the clavicular and upper sternal fibers insert most distally,
whilst the lower sternal and abdominal fibers insert proximaly.
One reliable landmark for the superior margin of the pectoralis insertion is the quadrilateral space,
best seen in the axial plane.
The superior edge of the pectoralis major insertion typically is identified at the level of,
or within 1-1.5 cm inferior to the quadrilateral space (range,
0-1.2 cm).
Another landmark is the origin of the lateral head of the triceps muscle.
The superior edge of the pectoralis major insertion is identified on the anterior aspect of the humerus,
approximately 5-10 mm superior to the level at which the lateral head of the triceps is first identified
MRI Technique
Connell et al.
(Radiology 210:785-791,
1999) described the proper technique used to image the pectoralis major.
MR studies are optimaly obtained using phased-array surface coil and planes coronal-oblique and axial,
with a combination of T1,
Stir and T2 sequences.
The tendon is normaly depicted as a low signal intensity structure,
it´s length is variable between 5 and 15 mm and the cephalocaudal dimension of the insertion ranges between 4 and 6 cm.
US Technique
Ultrasound imaging of the pectoralis muscle is optimaly obtained using a linear 5-12 Mhz transducer.
The three heads of the muscle have to be sacanned in both planes,
axial and longitudinal, at rest and dynamically.
In particular the pectoralis muscles are evaluated with the arm abducted and externally rotated (ABER position) to stress the myotendinous region.
Complete rupture
Complete ruptures tend to occur at the humeral insertion,
hemorrhage and edema are seen anterior to the humerus without visualization of the inserting pectoralis major tendon fibers,
the clavicular,
sternal or the entire tendon can be affected.
The tendon retraction can be depicted and measured.
Rupture of the sternal head occurs more frequently than rupture of the clavicular head(3),
although in older individuals the frequency of avulsion of the two major heads is probably the same. Often,
the intact clavicular portion makes the clinical diagnosis more difficult.
Partial ruptures
Partial ruptures are more common at the miotendinous junction,
it is crucial to scan the whole tendon distaly to exclude the possibiity of full thickness tear since partial ruptures are usually treated conservatively.
Postsugical evaluation
Surgical repair is used for full-thickness tears,
tears involving the distal tendon,
and injuries in athletes.
Several perils of delayed diagnosis exist,
including adhesions,
muscle retraction,
muscular scar and fibrosis,
atrophy,
and overall poor surgical outcome.
The ruptured tedon is usualy anchored to the humerus by means of a methalic plate.
Postoperative patiens are optimaly scanned using T1 and Stir secuences with high band width to avoid artifacts