Anatomy
The Pectoralis Major muscle demonstrated 2 divisions: a clavicular head (CH) and a sternal head (SH).
The CH constitutes a single architecturally uniform unit that cannot be further segmented.
In contrast, the SH can be divided along fascial planes into 6 or 7 muscle segments and constitutes approximately 80% of the total muscle volume.
The PM muscle fibers insert into a bilaminar tendon that consists of distinct anterior and posterior layers that are continuous inferiorly.
The anterior tendon layer receives muscular contributions from the entire CH and the most superior 3 to 5 muscle segments of the SH.
The posterior tendon layer receives muscular contributions from only the most inferior 2 to 3 SH segments. The posterior tendon layer extends about 11 mm more proximally on the humerus than the anterior layer
Pectoralis Major rupture
A rare injury caused by avulsion of the pectoralis major tendon, and usually seen in male weightlifters
Most commonly occurs as a tendinous avulsion
Sternocostal head of the pectoralis major tendon is the most common site of rupture
tendon fails in a predictable sequence: inferior fibers of sternocostal head fail first, then superior fibers of the sternocostal head, and finally the clavicular head
Symptoms
Patient may report a sudden pop or tearing sensation with resisted adduction and internal rotation
pain and weakness of shoulder
swelling and ecchymosis
“dropped nipple" sign
Palpable defect and loss of anterior axillary contour
weakness most pronounced in adduction and internal rotation
Ecchymosis + dropped nipple sign
Defect
Imaging
Xray : usually normal. May show humeral avulsion
MRI : exam of choice.
Requires dedicated sequence (standard shoulder MRI will not capture adequately)
T1 sequence fr chronic rupture. T2 for acute.
Classification
ElMaraghy, A. W., & Devereaux, M. W. (2012). A systematic review and comprehensive classification of pectoralis major tears. Journal of Shoulder and Elbow Surgery, 21(3), 412–422.
Timing: acute if less than 6 weeks
Extent : Width and Thickness
Location
It is difficult to assess the true extent of the rupture on the MRI : The final exact classification will be during the operation.
Intraoperative classification may be difficult with chronically scarred partial-thickness tears, because the torn tendon can often atrophy and retract (‘‘turtle’’) intramuscularly
Note the direction of any intact fibers. Fibers coursing in an inferolateral direction contribute to the anterior tendon layer, whereas superolaterally directed fibers contribute to the posterior layer.
Determine tear thickness by pinching the intact tendon from anterior to posterior. The mean thickness of each normal tendon layer is 2 mm; therefore, anything less than 4 mm suggests a partial-thickness tear.
The width of each normal tendon layer is approximately 4 cm. Measurement of the remaining tendon width will suggest incomplete vs complete tears.
Treatment
Initial sling immobilization, rest, ice, NSAIDs, physical therapy
Low-demand, sedentary, and elderly patients
Muscle belly tears, low-grade partial ruptures
Direct surgerical repair ( Delto-pectoral approach)
Tendon avulsion, myotendinous junction tears
Reconstruction
For chronic cases ( autograft or allo graft). Delto-pectoral approach)
