Anatomy of the Deltoid Muscle for Proper Vaccination Technique
Anatomy:
The deltoid muscle is divided into three parts on the basis of its three origins: anterior origin, acromial origin, and spinal origin. The anterior portion originates from the lateral 1/3 of the clavicle, the acromial portion originates from the acromion of the scapula, and the spinal part originates from the spine of the scapula. The fibers of the deltoid muscle join together to form a short tendon that inserts into the deltoid tuberosity, which is located on the lateral aspect of the humeral shaft. It is interesting to note that the deltoid muscle is called the deltoid because its shape resembles the Greek capital letter delta and also resembles the Delta Nile of Egypt. Keeping in line with this analogy, at the top of the delta, you will find the Mediterranean Sea which resembles the shoulder joint while at the bottom of the delta, you will find the river Nile, which resembles the nerves. The ideal injection site will be in the middle of the delta (i.e middle of the deltoid musculature) approximately 3-5cm below the acromion. The shape and morphology of the deltoid muscle that extends from anteriorly to posteriorly is such that it encircles the shoulder joint with the bulk of the muscle lying between the acromion and its insertion into the humerus. The shoulder and the deltoid muscle get its round appearance due to the deltoid passing over the upper part of the humerus (the humeral head. It is better from the patient to be wearing a short sleeve shirt that can be pulled up proximally so that the health care worker that is giving the vaccine can see the entire contour of the muscle and inject directly into the middle bulky portion of the muscle. Knowing the anatomy of this area is important to avoid the wrong location of injection.
Technique:
For deltoid intramuscular injection, you can use the square method or the triangle method for injection. Inject into the middle third of this structure. If you superimpose both injection techniques, the ideal site for injection remains about the same. Another vaccination technique is the “Z track” technique. The Z track technique will help in avoiding extravasation of the vaccine into the subcutaneous tissue, which minimizes irritation and inflammation of the subcutaneous tissue of the shoulder. First, put on clean gloves and then sterilize the skin. It is probably better to give the vaccine in the nondominant arm. Use a 20-25-gauge needle that is between 1-1 ½ inches in length to inject the vaccine. Withdraw the needle and release the skin. Alternatively, you can squeeze the muscle from front to back which is an old, traditional technique used by many practitioners so there will likely not be any difference between squeezing the muscle and using the Z track technique.
Complications:
1. Axillary nerve damage: There is a risk if you do not pull the sleeve proximal enough because you do not see the entire contour of the deltoid muscle and thus, the injection may be given too inferior. This presents as increased risk of damaging the neurovascular bundle. The site of vaccination should not exceed 5cm from the acromion (ideal site for injection) and this is because the nerve that supplies the deltoid muscle (axillary nerve) runs transversely from posterior to anterior about 7cm distal to the acromion. Injury of the axillary nerve will cause weakness of abduction of the arm due to atrophy of the deltoid muscle which will also have a flattened contour. There will also be a loss of sensation over the shoulder area.
2. Posterior circumflex humeral artery injury: Aspiration before injection is optional, but is not necessary in routine vaccination as it is rare to injure the artery during deltoid injection as the injection is usually superficial and not deep. The artery that is mentioned here is the posterior circumflex humeral artery which runs with the axillary nerve through the deltoid region.
3. SIRVA (Shoulder injury related to vaccine administration). SIRVA is a shoulder injury related to vaccine administration that occurs when you inject the vaccine either too high or too deep. In this case, the injection can go into the shoulder joint or the capsule, rather than into the substance of the deltoid muscle itself. Symptoms due to this condition include pain, inflammation, swelling, and decreased range of motion. Thankfully, SIRVA is a temporary self-limited condition which should improve after a few months though in some patients, the symptoms may last for several months.
