What is the insertion of the deltoid?

• A. Deltoid tuberosity
• B. Greater tubercle
• C. Lesser tubercle
• D. Olecranon process

Answer: (A)

Muscle insertion locations determine how a muscle pulls on a bone to produce movement. The deltoid attaches to a specific bump on the humerus called the deltoid tuberosity, located on the lateral midshaft of the bone. From that insertion, the deltoid can lift the arm (middle fibers), as well as flex and rotate it in various directions depending on which fibers are engaged. The greater and lesser tubercles are near the shoulder joint but are attachment sites for rotator cuff muscles, not the deltoid, and the olecranon process is at the elbow on the ulna, not related to the deltoid. So the insertion point for the deltoid is the deltoid tuberosity of the humerus.