Thickness of the Deltoid Muscle and Location of the Anterior Branch of the Axillary Nerve and the Posterior Circumflex Humeral Artery for Deltoid Injections

This study investigated the thickness of the deltoid muscle and the location of the anterior branch of the axillary nerve (AAN) and posterior circumflex humeral artery (PCHA), with the goal of maximizing the effectiveness of deltoid injections. Forty specimens from 22 adult Korean cadavers were used. A reference line was identified, connecting the anterior point of the deltoid muscle (AP) and the posterior point of the deltoid muscle (PP) on the surface. The midpoint between the AP and PP was used as the origin point (OP). The line connecting the OP and the lowest point of the deltoid tuberosity (DP) was used as the y-axis. The mean distance of the reference line from the AP to PP was 4.7 ± 0.7 cm. The vertical mean length of the deltoid muscle from the OP and DP was 16.1 ± 1.0 cm. At the 3, 5, and 7 cm sites, the thickness of the deltoid muscle was 0.62 ± 0.9, 0.73 ± 0.7, and 1.3 ± 1.1 cm, respectively. Most of the branches of the axillary nerve were concentrated in the third section (4-6 cm, 51%), while the branches of the PCHA were predominantly found in the fourth section (6-8 cm, 69%). The peripheral branches of the AAN entering the muscle were distributed between 2.2 and 9.8 cm from the acromion. The mean number of the peripheral branches of the AAN was 9.6 ± 3.4. In the deltoid muscle, the mean number of peripheral branches of the PCHA was 8.2 ± 2.8. Administering deltoid injections 5-6 cm below the OP is recommended to avoid axillary nerve injury.