Establishing a new appropriate intramuscular injection site in the deltoid muscle

Abstract

It is becoming increasingly important for clinicians to identify a safer intramuscular (IM) injection site in the deltoid muscle because of possible complications following the vaccine administration of IM injections. We herein examined 4 original IM sites located on the perpendicular line through the mid-acromion to establish a safer IM injection site. Thirty healthy volunteers participated in this study and the distances from our 4 IM sites to some anatomical landmarks on their left arms were measured. Ultrasonography (US) was also performed to measure the thickness of the deltoid muscle and identify the posterior circumflex humeral artery (PCHA) along the course of the axillary nerve. Subcutaneous thickness was measured using 2 methods: measuring the skin thickness with caliper after pinching the skin, and with US. The results obtained revealed that the intersection between the anteroposterior axillary line (the line between the upper end of the anterior axillary line and the upper end of the posterior axillary line) and the perpendicular line from the mid-acromion was the most appropriate site for IM injections because it was distant from the axillary nerve, PCHA, and subdeltoid/subacromial brusa. At this site, depth of needle insertions was 5 mm greater than the subcutaneous thickness at a 90° angle, which was sufficient to penetrate subcutaneous tissue in both sexes. Subcutaneous thickness can be assessed with almost the same accuracy by US or measuring with calipers after pinching the skin. The results of the present study support the improved vaccine practice for safer IM injections.

Keywords: Safe site for injection; axillary nerve; best practice; deltoid muscle; needle depth; nursing practice.

Figure 1.

Anatomical structure of the left shoulder (a) and locations of 4 examined sites in a living body (b). A: The upper end of the anterior axillary line, B: the upper end of the posterior axillary line, a: the anterior edge of the mid-acromion lateral border, C: Deltoid tuberosity for attachment of the deltoid muscle, b: the midportion of the mid-acromion lateral border, c: the posterior edge of the mid-acromion lateral border, a’: the intersection between the perpendicular line drawn from the anterior edge of the mid-acromion lateral border and line AB, b’: the intersection between a perpendicular line drawn from the mid-acromion lateral border and line AB, c’: the intersection between the perpendicular line drawn from the posterior edge of the mid-acromion lateral border and line AB, X: acromion, Y: subdeltoid/subacromial brusa, Z: humerus, dotted circle: the deltoid muscle, dotted line: the posterior circumflex humeral artery (PCHA), black line below the PCHA: the axillary nerve. (b) One third, half, and two thirds of bb’ are marked on the skin. 1/3 bb’, 1/2 bb’, 2/3 bb’, and b’ are the sites examined in the present study.

Figure 2.

Ultrasound image at 2/3 bb’. a: The posterior circumflex humeral artery (PCHA) (main trunk), b: PCHA (branch), c: superficial fascia, d: deep fascia, e: humerus, f: subcutaneous tissue, g: deltoid muscle, h: distance from the PCHA to 2/3 bb’, i: the site of 2/3 bb’.

Figure 3.

Distance from the posterior circumflex humeral artery (PCHA) to each examined site in males (a) and females (b). The location of the PCHA was expressed as 0 cm. a: p < 0.05, b: p < 0.01, (males; n = 13, females; n = 15, ANOVA, Tukey-Kramer HSD).

Figure 4.

Thickness of subcutaneous tissue and the deltoid muscle. (a) Subcutaneous thickness measured by calipers in males, (b) subcutaneous thickness measured by ultrasonography (US) in males, (c) subcutaneous thickness measured by calipers in females, (d) subcutaneous thickness measured by US in females, (e) The thickness of the deltoid muscle in males, (f) the thickness of the deltoid muscle in females. a: p < 0.05, b: p < 0.01, (males; n = 15, females; n = 15, subcutaneous thickness: Kruskal-Wallis and Steel-Dwass, thickness of the deltoid muscle: ANOVA, Tukey-Kramer HSD).

Figure 5.

Appropriate depth of the intramuscular (IM) injection at b’. The skin surface is expressed as 0 cm. The X axis shows each subject ID and the Y axis the depth from the skin surface. The black short lines are values that are 5 mm greater than the subcutaneous thickness measured by calipers, and represent the appropriate depth of needle insertion to administer IM injections. Black circles: subcutaneous thickness measured by ultrasonography (US), white triangles; subcutaneous thickness measured by calipers, black squares: the thickness of the deltoid muscle from the skin surface measured by US.