Botulinum Toxin Injection-Site Selection for a Smooth Shoulder Line: An Anatomical Study

Area of Science:

• Anatomy
• Cosmetic Surgery
• Neuroscience

Background:

• Manual needle placement into the trapezius muscle (TM) is essential for aesthetic shoulder contouring.
• Improving accuracy in TM injections can enhance cosmetic outcomes and patient satisfaction.

Purpose of the Study:

• To precisely map the anatomical distribution of nerve endings and neuromuscular junctions within the trapezius muscle.
• To identify optimal regions for needle insertion to achieve a smooth shoulder line in cosmetic procedures.

Main Methods:

• Macroscopic and microscopic analysis of trapezius muscle samples from cadavers.
• Sampling at four defined points along the muscle's origin to insertion line (0% to 100%).
• Quantification of nerve ending concentration and neuromuscular junction density.

Main Results:

• Macroscopic investigation revealed peak nerve ending concentration in the 60-80% region of the trapezius.
• Microscopic analysis confirmed the highest density of neuromuscular junctions in the 60-80% region.
• Similar, lower densities of neuromuscular junctions were observed in the 40-60% and 80-100% regions.

Conclusions:

• The 60-80% region of the trapezius muscle is the primary area for nerve endings and neuromuscular junctions.
• These findings provide crucial anatomical data for cosmetic surgeons performing TM injections.
• Optimizing needle placement based on these results can improve the accuracy and effectiveness of procedures for shoulder contouring.