Anatomical Variations of the Scalene Triangle: Dissection of 10 Cadavers

Study Design: Cadaver dissection to study the anatomy of the scaleni muscles and surrounding structures.

Objectives: To analyze in depth the anatomy of the scaleni muscles and surrounding structures, and to further document anatomical variations which have been reported in the literature.

Background: The literature reported variations in the attachments of the scaleni muscles, as well as the presence of a scalenus minimus muscle. The importance of these muscles in the respiratory and musculoskeletal systems led us to study these muscles with dissection.

Methods And Measures: We performed anatomical dissection on 10 cadavers. The findings from the cadavers were analyzed and reported.

Results: The attachments of the 3 primary scaleni muscles (anterior, medius, and posterior) were variable. The actual width of the scaleni muscles (anterior, medius, and posterior) at the C6 tubercle and at the first rib also varied. A scalenus minimus was present in one cadaver and presumably present in 2 others. The scalenus anterior muscle arose in 20% of the specimens from C3 to C6, in 30% of the specimens from C3 to C7, in 20% of the specimens from C4 to C5, and in 30% of the specimens from C4 to C6. The scalenus anterior muscle arose from C3 in 50% of the dissections. An attachment to C7 was observed in 30% of the cadavers. The widths of the scalenus anterior muscles at their insertion were between 8 and 17 mm. The scalenus medius muscle arose in 40% of the specimens from C2 to C6. In 60% of the cadavers, the scalenus medius muscle had an attachment to C7. Fifty percent of the scalenus medius muscles arose from C2 and 50% also had an origin from C1. The widths of the scalenus medius muscles at their insertion were between 10 and 20 mm with a mean of 15.5 mm. Fifty percent of the scalenus posterior muscles arose from C4 to C6 and 50% arose from C5 to C6.

Conclusions: Variations were found in the attachments and the size of the scaleni muscles. These variations may effect the size of the scalene triangle, and thus, may potentially result in varied signs and symptoms in patients who have cervical, thoracic, and rib dysfunctions. Clinical implications were postulated.