The Basics of Intramuscular Injections: Understanding Risks and Best Practices

Intramuscular injections are required by even the healthiest of individuals, whose most frequent encounters with medical professionals are often focused on the need of these treatments in the form of flu shots or other basic immunizations. IM injections are crucial for ease of administration day-to-day usage because they allow medication to be absorbed into the bloodstream quickly through muscle fibers.[1] Due to the frequency of their use, it is critical to understand the basics of normal, safe administration as well as the risks that can come from improper administration in order to recognize discrepancies and understand unexpected complications brought to light in a legal setting. Therefore, this post will outline the basics of the procedure as well as some potential consequences for improper IM injections.


Injection Sites

To determine which injection site to use, the type of medication used, its volume, and the patient’s age and condition must be taken into consideration.[2] The following four areas are where intramuscular injections are typically given:

  • Deltoid muscle: located in the arm, this is the site most commonly used for vaccines. However, its small muscle mass limits the volume of medication that can be injected (typically no more than 1mL).[3]
  • Vastus lateralis muscle: this is a muscle in the thigh, and is used when other sites are not available or if the medication is to be self-administered.[4] This is the recommended site for injections of up to 5mL in volume due to the fact that the muscle is much bigger.[5]
  • Ventrogluteal muscle: the safest site for adults and children over seven months, this muscle in the hip is deep and not close to any major blood vessels or nerves.[6] It is also more likely to reach the muscle for which is intended and sufficient evidence to use this site whenever possible.[7] The recommended volume for an injection here is between 2.5 and 3mL.[8]
  • Dorsogluteal muscle: located in the buttocks, this was the site most commonly selected by healthcare providers until the past decade.[9] Recently, there are considered no advantages to using this site with greater emphasis placed on using the vetrogluteral site instead for deep IM injections due to the slower absorption rate using this muscle as well as risk to sciatic nerve injury, identified as a serious complication of iatrogenic injury.[10] Volumes of up to 4mL can be administered here however because of the larger muscle size.[11]



For each site, it is critical for nurses to be able to identify the prominent bones and anatomical landmarks to locate the proper muscle accurately and with confidence.[12] The needle used must be of a size sufficient enough to penetrate the fat and travel into the muscle level, but not so long as to pierce the nerve or blood vessels underneath.[13] Additionally, different needle sizes will be needed for children (typically 16mm is recommended) and based on sex (women weighing between 60 and 90kg have more fatty tissue).[14] The patient should be positioned so that the muscle is relaxed, the injection should be made in a “dart-like” action, and the needle should be removed after waiting ten seconds so as to prevent leakage of the medication.[15] The Z-track method of injection is another way to reduce leakage of medication while decreasing skin lesions at the injection site; the nurse displaces the tissue before inserting the needle, then once the needle is withdrawn, the tissue is restored to its normal position.[16]


Risks and Complications

Most of the adverse events caused by IM injections are the result of poor practice – poor technique, lack of understanding, and a general lack of skill or confidence on a nurse’s part are typically to blame.[17] Injury to peripheral nerves, blood vessels, bones, as well as muscle fibrosis, tissue necrosis, abscess, cellulitis, granuloma, contractures, hematoma, and sometimes tendonitis are all possible risks.[18]


In addition to the above mentioned issues, there is a potential for shoulder injury related to vaccine administration, or SIRVA; this can be caused by a vaccine injected too high up on the arm, and this risk receiving publicity due to its rising numbers.[19] SIRVA occurs when the needle intended for the arm muscle instead goes into the bursa, the fluid-filled sac protecting the shoulder tendons, and the immune system is provoked to attack the bursa.[20] This leads to pain and sometimes a frozen shoulder which patients may or may not be able to recover from.


Due to the immense frequency with which intramuscular injections are performed, it is both not surprising there are occasional mistakes made, but also crucial that these mistakes be rectified. Your client deserves to know that what they have might not just be a sore shoulder, but a serious medical condition. Know the best practices as well as the risks, and more patients can be spared the unnecessary complications that can accompany poorly administered IM injections.

[1][1] Ogston-Tuck, S, “Intramuscular injection technique: an evidence-based approach,”  in Nursing Standard  (RCN Publishing, July 4, 2014), 52-59

[2] Ibid

[3] “What Are Intramuscular Injections?”, n.d.,

[4] Ibid

[5] Orgston-Tuck, “Intramuscular injection technique”

[6] “What Are Intramuscular Injections?”


[8] Orgston-Tuck, “Intramuscular injection technique”

[9] “What Are Intramuscular Injections?”

[10] Ogston-Tuck, “Intramuscular injection technique”

[11] Ibid

[12] Ibid

[13] Ibid; “What Are Intramuscular Injections?”

[14] Ogston-Tuck, “Intramuscular injection technique”

[15] Ibid

[16] Ibid

[17] Ibid

[18][18] Ibid

[19] Zhang, Sarah, “Why are cases of shoulder injuries from vaccines increasing?”, Sept. 3, 2015,

[20] Ibid