Intramuscular Injection Sites 3D Explorer

Where are the intramuscular injection sites?

Open RN names three: the deltoid of the upper arm, the ventrogluteal site on the side of the hip, and the vastus lateralis on the outer thigh. Each is found from bony landmarks. StatPearls still lists the dorsogluteal site in the upper outer buttock among the most commonly used, while saying the ventrogluteal site has a better safety profile. The dorsogluteal site is avoided because of the risk to the sciatic nerve: dorsogluteal injections account for most injection injuries of the nerve (StatPearls), the quadrant is easy to misjudge (StatPearls, sciatic nerve), and Open RN says to avoid the site.

Which site is safest, and which is routine

Open RN and StatPearls both call the ventrogluteal site the safest. Open RN says it has the greatest thickness of gluteal muscle, is free from penetrating nerves and blood vessels, and has a thin layer of fat; StatPearls points to its thin subcutaneous layer and relatively large gluteus medius, and says it may be safer than the dorsogluteal site in older adults because of the lower risk of contacting bone. Open RN generally recommends it for IM medicines in adults, and prefers it for oily or irritating solutions at any age. Sources differ on oily medicines: StatPearls lists “suspensions and oily medications cannot be administered” among the disadvantages of IM injection, though it names benzathine penicillin and testosterone among the most common IM medicines. The CDC recommends the deltoid for routine adult vaccines and, for the majority of infants, the anterolateral thigh (the vastus lateralis, in Open RN’s words), and prefers the deltoid from age 3.

How far below the acromion is the deltoid site

About 2 to 3 fingerbreadths, roughly 2 inches, below the acromion and above the level of the armpit, in the thickest part of the muscle, per Immunize.org. StatPearls and Open RN give 1 to 2 inches (2.5 to 5 cm). StatPearls also calls the safest point approximately 7 to 13 cm below the midacromial point and midway between the acromion and the deltoid tuberosity, and cites no source for that figure, so the sources differ on how far down to go. They differ on the landmark too: Nakajima 2017 found the axillary nerve often runs near the site 5 cm below the mid-acromion, called that site unsuitable, and uses the point where a line straight down from the mid-acromion crosses the line joining the upper ends of the anterior and posterior axillary lines, which StatPearls also calls safe. Immunize.org says not to inject too high (near the acromion) or too low, to avoid causing an injury. StatPearls reports shoulder injury and radial nerve injury after deltoid injection, and Cook 2015 says the radial nerve and the anterior branch of the axillary nerve are susceptible to injury from it.

On the model the deltoid’s insertion at the tuberosity is 13.9 cm below the acromion, so midway is about 7 cm, and 13 cm is within 1 cm of the insertion, by the radial nerve pin, which Cook 2015 supports: the nerve is at risk above and in the spiral groove, which ends just below the deltoid tuberosity. Immunize.org, Open RN and StatPearls’s own site description keep to about 2 inches (5 cm) or less. The zone is the band 2.5 to 5 cm below the acromion on the deltoid’s outer face, centered 3.7 cm down. Nakajima 2017 gives the subacromial bursa a mean 4.0 cm in women and 4.1 cm in men from the mid-acromion, inside that band. The band painted as too high, 0.5 to 2 cm below the acromion, is ScienceQuest’s drawing of Immunize.org’s “near the acromion”; no source gives a figure.

Why the dorsogluteal site is avoided

Because of the sciatic nerve. It usually leaves the pelvis through the greater sciatic foramen below piriformis, under the buttock; StatPearls’s sciatic nerve chapter says that in 10% it passes through or above the muscle. If a needle hits it the patient may have partial or permanent paralysis of the leg, so Open RN says to avoid the site and StatPearls says the ventrogluteal site has a better safety profile. The sciatic nerve chapter adds that injecting the inferomedial buttock puts the nerve at risk, and that many people have a fatty bulge there, so the “upper and outer” quadrant is easy to misjudge; the model’s hollow pin sits on piriformis’s lower border at the greater sciatic notch. StatPearls’s intramuscular injection chapter says the sciatic nerve, particularly its peroneal division, is the nerve most often injured by injection, and that dorsogluteal injections account for most of its injection injuries. The CDC’s infant guidance says that if the gluteal muscle is chosen, the injection goes lateral and superior to a line from the posterior superior iliac spine to the greater trochanter, the line the model draws. The zone painted to avoid is that CDC region, not StatPearls’s site 5 to 7.5 cm below the iliac crest.

Volume and needle ranges, and where sources differ

Open RN gives the maximum for a single adult injection as generally 1 mL in the deltoid, 3 mL in an average adult at the ventrogluteal site, and 3 mL in adults at the vastus lateralis. For any IM site, it says older adults and thin patients may only tolerate up to 2 mL, and gives 0.5 to 1 mL at one site in infants and children. Its general statement that adults tolerate 2 to 3 mL is not a deltoid figure, and the CDC, Immunize.org and StatPearls give no deltoid volume. Needle length for vaccines follows the CDC’s Table 6-2, by age and, for adults, by sex and weight, from 5/8 in (16 mm) in a newborn’s thigh to 1.5 in (38 mm) in the deltoid of a woman over 200 lb (90 kg) or a man over 260 lb (118 kg). The sources differ at the edges: under 130 lb (60 kg) the CDC’s table gives 1 in (25 mm) while its text calls 5/8 in sufficient, Open RN calls 1 in sufficient for men up to 260 lb, Immunize.org starts the CDC’s 152 lb rows at 153 lb, StatPearls gives children 25 to 38 mm, and Kutaish 2025, which found a standard needle reached the subacromial space in 51.9% of 177 shoulder-surgery patients, recommends a shorter 15 mm needle for most adults, so the card names each. The CDC, Immunize.org, Open RN and StatPearls all give a 90° angle.

What the model can and cannot show

The ventrogluteal triangle is placed on this body’s own anterior superior iliac spine, the tubercle of its iliac crest (4.6 cm from the spine) and the upper border of its greater trochanter. In this one model, the surface nearest the skin across the triangle is 40.0 percent tensor fasciae latae, 38.5 percent gluteus medius and minimus, and 21.5 percent bare bone at the crest, so on this body tensor fasciae latae covers the front of the triangle. The zone is painted only where gluteus medius or minimus is that surface, which puts its center 1.3 cm behind the center of the triangle, and tensor fasciae latae is drawn as glass. The thigh zone is the middle third of the 36 cm from the greater trochanter to the lateral femoral condyle. The meshes are from one adult male volunteer, segmented from MRI, without skin, fat or nerves: they show where the landmarks are, not how deep a needle must go in anyone.

Sources

CDC and ACIP, General Best Practice Guidelines for Immunization: Vaccine Administration, with Table 6-2 on needle length and site. Immunize.org, How to Administer Intramuscular and Subcutaneous Vaccine Injections, item P2020 (10/17/2026). Munakomi S and Gillespie E, Intramuscular Injection, StatPearls (updated September 13, 2026). Ernstmeyer K and Christman E, editors, Nursing Skills, 2nd edition, Open RN, WisTech Open, 2023, section 18.6, Administering Intramuscular Medications. Giuffre BA, Black AC and Jeanmonod R, Anatomy, Sciatic Nerve, StatPearls (updated November 16, 2023). Nakajima Y, Mukai K, Takaoka K and others, Establishing a new appropriate intramuscular injection site in the deltoid muscle, Human Vaccines and Immunotherapeutics 2017;13(9):2123-2129. Cook IF, Best vaccination practice and medically attended injection site events following deltoid intramuscular injection, Human Vaccines and Immunotherapeutics 2015;11(5):1184-1191. Kutaish H, Bouché PA, Rivera PM and others, More than half of shoulder vaccinations may end up in the subacromial space, NPJ Vaccines 2025;10:229. The zones and landmark positions are this site’s measurement of the BodyParts3D meshes.