1. Muscle: Vastus lateralis; 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
How to locate: To landmark the vastus lateralis, position the patient lying down or being held by a parent. Palpate the muscle below the greater trochanter and above the lateral femoral condyle (knee joint). Divide the muscle into thirds and administer the injection into the middle third of the muscle, in the outer anterolateral aspect, lateral to the midpoint of the thigh.
2. Muscle: Deltoid; 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 join
How to locate: The deltoid muscle is a rounded triangle shape. To landmark this site, the patient should be sitting comfortably with their arm visible from the shoulder to the top of the elbow. Palpate the acromion (outer edge of the scapula) and trace an imaginary inverted triangle below the shoulder. The injection should be given 3-5cms below the acromion, in the middle of the triangle.