Intramuscular neural distribution revealed by Sihler’s method: Application to botulinum neurotoxin injection in shoulder and arm contouring

Abstract

The use of botulinum neurotoxin in body contouring is increasing with time. Body contouring usually targets the superior trapezius, deltoid, and lateral head of the triceps brachii, as hypertrophy in these muscles gives the arms and shoulders a “muscular” appearance, which raises cosmetic concerns, especially in women. We propose an ideal botulinum neurotoxin injection point for the superior trapezius, deltoid, and lateral head of the triceps brachii muscles for shoulder and arm aesthetic line contouring, describing the intramuscular nerve branching in these muscles, providing essential information for botulinum neurotoxin injection. A modified Sihler’s method was performed on the superior trapezius, deltoid, and lateral head of the triceps brachii muscles in 16, 14, and 16 specimens, respectively. Intramuscular arborization of the superior trapezius muscles was examined regarding the external occipital protuberance superiorly and the horizontal line crossing the acromion of the scapula. Intramuscular arborization of the deltoid muscles was demarcated using the marginal line of the muscle origin, and the line connecting the anterior and posterior upper edges of the axillary region. Intramuscular arborization of the triceps brachii muscle of the lateral head was measured as the distance from the lateral epicondyle to the anteroinferior point of the acromion. The intramuscular neural distribution had the greatest arborized patterns in the horizontal (1/5–2/5) and vertical (2/4–4/4) sections for the superior trapezius muscle, in the area between the horizontal 1/3 to 2/3 lines of the anterior and posterior deltoid bellies in the deltoid muscle, and 2/3 to the axillary line in the middle deltoid muscle. Intramuscular arborization patterns of the triceps brachii were observed at the lateral heads of 4/10–7/10. These areas, corresponding to the areas of maximum arborization, are recommended as the most effective and safe points for botulinum toxin injection.