Chanwit Maneenin; Naowarat Maneenin; Chananya Jirapornkul; Chadaporn Chaimontri & Sitthichai Iamsaard

This study aimed to classify and investigate anatomical variations of the sternocleidomastoid (SCM) muscle, which is commonly used as an anatomical landmark to indicate the correct position for central venous catheterization, in a Thai population. Thirty- five embalmed cadavers from the Northeast Thailand (19 females and 16 males) were systemically dissected to reveal the SCM muscles in both sides for gross human anatomy teaching. Variations in the SCM origin and insertion were observed and recorded. The prevalence of anatomical variations was approximately 11.4 % (4 of 35 cadavers) and was not different by sex. Such variations were classified into 5 types based on origin, insertion, and presence of additional heads, as follows: type I (n=31; 88.6 %), type II (n=1; 2.85 %), type III (n=1; 2.85 %), type IV (n=1; 2.85 %), and type V (n=1; 2.85 %). Clinical considerations and prevalence of variant SCM muscle have also been discussed. Since the incidence of this anatomical variations was more than 10 %, the cervical surgeons should seriously consider this issue before insertion of a central venous catheter to avoid complications.

KEY WORDS: Sternocleidomastoid muscle; Anatomical variation; Cadavers; Classification.

MANEENIN, C.; MANEENIN, N.; JIRAPORNKUL, C.; CHAIMONTRI, C. & IAMSAARD, S. Classification of sternocleidomastoid muscle variations and comparison of its incidence among populations. Int. J. Morphol., 41(1):175-180, 2023.