1. Site: Anterolateral thigh
Muscle: Vastus lateralis muscle
Origin: Greater trochanter and linea aspera of femur.
Insertion: Patella via quadriceps tendon and then tibial tuberosity via patellar ligament.
Action: All four heads extend leg at knee joint; rectus femoris muscle acting alone also flexes thigh at hip joint.
To locate: Divide the thigh into thirds. The injection site should be in the distal third of the thigh, which corresponds to the vastus lateralis muscle.
2. Muscle: Deltoid muscle
Origin: Acromial extremity of clavicle (anterior fibers), acromion of scapula (lateral fibers), and spine of scapula (posterior fibers).
Insertion: Deltoid tuberosity of humerus
Action: Lateral fibers 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.
To locate: 1-2 inches below the acromion process