1. For infants, the site of injection is the lateral or outer thigh
- The targeted muscle is Vastus lateralis muscle
- Origin: the greater trochanter and the lateral lip of linea aspera of the femur.
- Insertion: patella
- Action: Extension of knee joint and stabilizing the patella
- The muscle is located on the anterior lateral aspect of the thigh and extends from one hand's breadth above the knee to one hand's breadth below the greater trochanter. To find the muscle, gently palpate the side of the thigh just below the greater trochanter and then divide the thigh into three equal parts vertically. The injection site is usually in the middle third of this muscle.
2. The preferred site for intramuscular injection is the Deltoid
- Origin: Lateral 1/3 of Clavicle, Acromion, Spine of Scapula
- Insertion: Deltoid tuberosity of humerus
- Action: flexion and internal rotation of the arm, abduction of the arm, and extension and external rotation of the arm.
- To locate this muscle, palpate the shoulder below the acromion and divide it into three equal parts vertically. The outer third is typically used for intramuscular injections.