Qualitative and Quantitative Anatomy of the Proximal Humerus Muscle Attachments and the Axillary Nerve: A Cadaveric Study

Purpose: To provide a quantitative and qualitative anatomic analysis of the pectoralis major, teres major, and latissimus dorsi on the humerus, as well as the deltoid tendinous attachments on the proximal humerus and acromion, and to quantitatively characterize the humeral course of the axillary nerve. Methods: Ten nonpaired, fresh-frozen human cadaveric shoulders were analyzed. A portable coordinate-measuring device quantified the location of bony landmarks and tendon attachment areas. The tendon footprints were recorded by tracing their outlines and center points. The footprint areas of the tendons, the distances between the footprint areas and pertinent osseous and soft-tissue landmarks, and the distance between where the axillary nerve courses across the humerus relative to the acromion and greater tuberosity were measured. Results: Of the 10 specimens, 9 (90%) had 5 distinct tendinous bands attaching the deltoid to the acromion; 1 specimen had 4 bands. The distances between the center of the deltoid footprint on the humerus and the centers of the pectoralis major, latissimus dorsi, and teres major tendon footprints on the humerus were 43.5 mm, 58.5 mm, and 49.4 mm, respectively. The shortest distances from the perimeter of the pectoralis major to the latissimus dorsi and teres major tendon footprints were 3.9 mm and 9.5 mm, respectively. The distance from the superior aspect of the greater tuberosity to the axillary nerve on the humeral shaft was 50.3 mm (95% confidence interval, 47.0-53.5 mm). The distance from the lateral acromion to the axillary nerve was 69.3 mm (95% confidence interval, 64.1-74.5 mm). Conclusions: The deltoid muscle had 4 to 5 tendinous insertions on the acromion, and the axillary nerve was 50.3 mm from the tip of the greater tuberosity. The distance between the lower border of the pectoralis major and the axillary nerve was 9.4 mm. Clinical Relevance: Knowledge of the quantitative anatomy of the tendons of the proximal humerus and axillary nerve can aid in identifying structures of interest during open shoulder surgery and in avoiding iatrogenic axillary nerve injury. Furthermore, this study provides direction to avoid injury to the deltoid tendons during open surgery.