From the Guidelines
Intramuscular injections should be administered at a 90-degree angle to the skin surface. This approach is crucial for ensuring the medication is delivered deep into the muscle tissue, maximizing absorption and efficacy. When administering an intramuscular injection, the healthcare provider should first clean the injection site with an alcohol swab, pinch or stretch the skin depending on the patient's body composition, and then insert the needle quickly and firmly at the 90-degree angle. The needle length should be appropriate for the patient's size and the injection site, typically 1-1.5 inches for adults, as suggested by the American Academy of Family Physicians (AAFP) and the Advisory Committee on Immunization Practices (ACIP) 1. Common intramuscular injection sites include the vastus lateralis (thigh), ventrogluteal (hip), dorsogluteal (buttock), and deltoid (shoulder) muscles. Key considerations for the injection site include:
- The deltoid muscle is recommended for routine intramuscular vaccinations in adults, according to the AAFP and ACIP 1
- The anterolateral thigh can be used as an alternative site
- The suggested needle size is 1--1½ inches and 22--25 gauge, as recommended by the AAFP and ACIP 1 The 90-degree angle maximizes medication absorption through the rich blood supply of muscle tissue, allowing for faster onset of action compared to subcutaneous injections and the ability to administer larger volumes of medication.
From the Research
Intramuscular Injection Angle
- The recommended angle for intramuscular injections is a topic of discussion among medical professionals, with some studies suggesting a 90-degree angle 2 and others proposing a more relaxed standard between 72 degrees and 90 degrees 3.
- A study published in 2002 found that the evidence supports a 90-degree angle of needle insertion for intramuscular injection as being the most effective in terms of patient comfort, safety, and efficacy of vaccine 2.
- However, another study published in 2000 argued that the 90-degree angle requirement is unrealistic and that an injection given at 72 degrees reaches 95% of the depth of an injection given at 90 degrees 3.
- There is no direct evidence in the provided studies to suggest a specific angle for intramuscular injections, but the studies do discuss the importance of proper technique to avoid complications such as nerve injury 4, 5.
Complications of Intramuscular Injections
- Nerve injury is a common complication following intramuscular injection, with the sciatic nerve being the most frequently affected nerve 4, 5.
- A study published in 2014 found that sciatic nerve injection injury is a preventable event and that total avoidance of intramuscular injection is recommended if other administration routes can be used 4.
- Another study published in 2006 found that nerve injuries following intramuscular injections carry a poor prognosis, with only 28% of patients having a good recovery 5.
- Bleeding complications following intramuscular injections are generally considered rare, with a reported incidence of 0.06% 6.