1. The injection site for the infant is the anterolateral thigh in which the target muscle is the vastus lateralis, a thigh muscle.
- Origin: Greater trochanter and linea aspera of femur
- Insertion: Patella via quadriceps tendon and then tibial tuberosity via patellar ligament.
- Action: Extend leg at knee joint; rectus femoris muscle acting alone also flexes thigh at hip joint.
- How to locate: Located on the outside part of the thigh
2. The safest injection site for adults is the deltoid.
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Origin: Acromial extremity of clavicle (anterior fibers), acromion of scapula (lateral fibers), and spine of scapula (posterior fibers)
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Insertion: Deltoid tuberosity of humerus
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Action: Lateral fi bers abduct arm at shoulder joint; anterior fibers flex and medially rotate arm at shoulder joint; posterior fibers extend and laterally rotate arm at shoulder joint
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How to locate: Expose the upper arm and find the acromion process by palpating the bony prominence; approximately 2–3 finger widths below the acromion process