Deltoid Muscle: Anatomy, Function & Injection Site

The deltoid muscle is a thick, triangular muscle covering the shoulder (anterior, lateral, posterior). It comprises three parts: anterior, lateral, and posterior deltoid.

Functions

• Abduction (arm away from body)
• Flexion (bending elbow)
• Extension (straightening elbow)
• External rotation (arm away from body)
• Internal rotation (arm toward body)

Innervated by the axillary nerve.

Clinical Significance

• Common injection site (vaccines, blood draws)
• Injuries from trauma, overuse, shoulder instability