Qualitative and Quantitative Anatomy of the Humeral Attachment of the Pectoralis Major Muscle and Structures at Risk: A Cadaveric Study

Abstract

Background: Surgical pectoralis major (PM) repair can offer improved functional outcomes over nonoperative treatment. However, there is a lack of literature on consensus of the anatomical site of the humeral attachment. Purpose: To provide qualitative and quantitative anatomic analysis of the PM by focusing on humeral insertion and relevant structures at risk. Study Design: Descriptive laboratory study. Methods: Eight fresh-frozen male cadavers were dissected. The relevant landmarks that were collected and measured included (1) PM footprint length at the humeral insertion (total, sternal head, and clavicular head insertions); (2) PM tendon length from the humeral insertion to the musculotendinous junction; (3) distance from the PM humeral insertion to the lateral (LPN) and medial (MPN) pectoral nerves; and (4) distance from the coracoid process to the musculocutaneous nerve (MCN) in anatomical position. Results: The total PM footprint length was 81.4 mm (95% CI, 71.4-91.3). The sternal and clavicular heads that make up the PM had footprint lengths of 42.1 mm (95% CI, 32.9-51.4) and 56.6 mm (95% CI, 46.5-66.7), respectively. The PM tendon was wider at the clavicular head (74.7 mm; 95% CI, 67.5-81.7) than the sternal head insertions (43.0 mm; 95% CI, 40.1-45.9). The distances from the PM humeral insertion to LPN and MPN were 93.2 mm (95% CI, 83.1-103.3) and 103.8 mm (95% CI, 98.3-109.4), respectively. The coracoid process to MCN distance was 68.5 mm (95% CI, 60.2-76.8). Conclusion: This study successfully quantifies anatomic dimensions of the PM tendon, its sternal and clavicular head insertions, and its location relative to nearby vital structures. Such knowledge can provide surgeons with a better understanding of the PM in relation to nearby neurovascular structures during anatomic PM repair and reconstruction to avoid debilitating complications. Clinical Relevance: Knowledge of the quantitative anatomy of the PM at the humeral footprint along structures at risk may aid surgeons with identifying the injured part of the PM and improve outcomes for anatomic repair and reconstruction.

Myotendinous junction tears of the pectoralis major are occurring more frequently and discrepancies exist between intraoperative and radiographic assessments

“… 22 , 24 This may explain why excessive eccentric loading during weightlifting with the shoulder abducted and externally rotated, such as when performing bench press, is one of the most common mechanisms of injury resulting in PM tears. 10 , 16 , 22 …”

“… 9 , 24 Measurement of the mean distance from the superior to inferior aspect of the humeral footprint revealed that the SH insertion of the PM tendon was located at a distance of 42.1 mm, while the CH insertion was located at a mean distance of 56.6 mm. 10 At the level of the MTJ, the 2 heads were fused, and the CH insertion was found to be longer than the SH insertion, measuring 56.6 mm and 42.1 mm, respectively. Additionally, a tendon overlap footprint length of 27.9 mm was observed.…”