Standardization of sternocleidomastoid for botulinum toxin applications*

Abstract

Objectives: Botulinum toxin is frequently applied to the sternocleidomastoid muscle (SCM) for torticollis treatment. Duringthis application, bulb of the jugular vein located under SCM makes the interventions unsafe. Also, injecting the botulinumtoxin into the infrahyoid muscles which lie under SCM may cause hoarseness and swallowing disorders. The aim of this studywas to describe the most reliable and appropriate botulinum toxin injection sites to the SCM to avoid injury to neighboringneurovascular structures and adjacent muscles.Methods: In ten male cadavers, SCM was evaluated in three equal segments (upper, middle and lower). Muscle width and thicknessat the center of each segment were measured. In one male cadaver, colored latex was injected according to the results ofthe measurements.Results: The respective mean width of upper, medial and lower segments were 33.15 (23–41) mm, 36.45 (28–45) mm and,39.35 (15–50) mm, respectively. The mean thickness of upper, medial and lower segments were 5.29 (3.87–7.68) mm, 5.89(3.56–8.32) mm and 3.60 (0.69–7.75) mm, respectively. There was no significant difference between the right and left sides.The thickest part of the muscle was the middle part, and the lower part was the thinnest. When the colored latex injected cadaverwas dissected, the center of the muscle was observed as colored, while the neighboring structures were avoided. The thickestand safest part of SCM for the botulinum toxin injections was the middle part.Conclusion: Knowing the thickness of SCM will make the botulinum toxin applications to this muscle safer and easier.