Anatomical variations of the scalene triangle: Dissection of 10 cadavers

Study Design: Cadaver dissection to study the anatomy of the scaleni muscle s and surrounding structures. Objectives: To analyze in depth the anatomy of the scaleni muscles and surr ounding structures, and to further document anatomical variations which hav e been reported in the literature. Background: The literature reported variations in the attachments of the sc aleni muscles, as well as the presence of a scalenus minimus muscle. The im portance of these muscles in the respiratory and musculoskeletal systems le d us to study these muscles with dissection. Methods and Measures: We performed anatomical dissection on 10 cadavers. Th e 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 (an terior, medius, and posterior) at the C6 tubercle and at the first rib also varied. A scalenus minimus was present in one cadaver and presumably prese nt in 2 others. The scalenus anterior muscle arose in 20% of the specimens from C3 to C6, i n 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 a rose 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 mediu s muscle had an attachment to C7. Fifty percent of the scalenus medius musc les arose from C2 and 50% also had an origin from C1. The widths of the sca lenus medius muscles at their insertion were between 10 and 20 mm with a me an of 15.5 mm. Fifty percent of the scalenus posterior muscles arose from C 4 to C6 and 50% arose from C5 to C6. Conclusions: Variations were found in the attachments and the size of the s caleni muscles. These variations may effect the size of the scalene triangl e, and thus, may potentially result in varied signs and symptoms in patient s who have cervical, thoracic, and rib dysfunctions. Clinical implications were postulated.