Localization of the Center of Intramuscular Nerve Dense Regions in Deltoid Muscle: An Applied Anatomical Study

Accurately locating the central intramuscular nerve dense region (CINDR) within the deltoid muscle is essential for safe and effective intramuscular drug injections.Improper targeting increases the risk of nerve injury, whereas accurate localization provides valuable guidance for routine drug injections and specific botulinum toxin therapy.This study examined 24 adult cadavers to determine the location of the CINDR within the deltoid muscle.A longitudinal reference line (L-line) was drawn between the acromion and lateral epicondyle of the humerus, and a semicircular transverse reference line (H-line) was drawn from the lowest point of the jugular notch, passing through the acromion to the medial end of the scapular spine.Sihler's staining was used to visualize the intramuscular nerve-dense regions, and barium sulfate was applied to mark the CINDR.Spiral computed tomography (CT) scans and the Syngo system were used to record the projection point of the CINDR on the body surface, designated as point P. The intersection of the vertical line through point P with the H-line and the horizontal line with the L-line were designated as PH and PL, respectively.The percentage positions of PH and PL along the H-line and L-line, as well as the depth of the CINDR were measured and analyzed.The anterior, middle, and posterior parts of the deltoid muscle contained a distinct intramuscular nerve-dense area.The PH points of the CINDR were located at 45.52 %, 54.76 %, and 76.19 % along the H-line, whereas the PL points were located at 18.99 %, 23.65 %, and 22.16 % along the L-line.The CINDR depths were 1.08 cm, 1.99 cm, and 1.44 cm, respectively.All percentages represent mean values.The identified CINDR locations should be avoided during routine intramuscular drug injections and should serve as effective targets for botulinum toxin-based shoulder slimming procedures and the treatment of muscle spasms.