The deltoid muscle: an anatomic description of the deltoid insertion to the proximal humerus.

OBJECTIVE This study was designed to describe the anatomic insertion point of the deltoid to the proximal humerus. DESIGN Gross anatomic study. SETTING Level one academic trauma center. PATIENTS Cadaveric study. MAIN OUTCOME MEASUREMENTS Bilateral humeri were stripped of soft tissue except the deltoid insertion point. The length of the humeri was recorded. The distance from the greater tuberosity to the proximal most aspect of the tendinous insertion point and the distal most tendinous attachment was measured. The humeri were cross-sectioned 5-mm distal to the proximal insertion point, 5-mm proximal to the distal insertion point, and midway between these 2 points. The circumferential proportion of humerus into which the tendon inserted at each point was recorded. RESULTS The mean length of the deltoid insertion was 97 (range, 83-111) mm. The mean distance from the greater tuberosity to the proximal insertion point was 61 (range, 55-75) mm and to the distal insertion was 158 (range, 142-172) mm. The deltoid occupied on average: 8% of the humeral circumference 5 mm from the proximal insertion point, 39% at the mid point of the insertion, and 31% of the humeral circumference 5 mm from the distal insertion point. CONCLUSIONS The deltoid insertion is long and broad. A 4.5-mm plate would result in detaching 13.5 mm of the insertion, leaving at least half of the original insertion attached to the humerus.