The muscular floor of the triangle comprises (from superior to inferior): splenius capitis, levator scapulae, and scalenus medius and posterior (Bruce et al 1967, Drake et al 2005, Grant and Basmajian 1965, Last 1978, Moore and Dalley 2006, Wood Jones 1953, Woodburne and Burkel 1988, Zuckerman 1961) (see Figure 1).
The location of scalenus anterior with respect to the posterior triangle is consistently reported in anatomical texts.
Consultation of the surgical literature confirms that scalenus anterior lies deep to the clavicular head of SCM, and gives further insight: Mattson (2004) in an article on the surgical approach to anterior scalenectomy clearly describes how the surgeon must progress through the skin, platysma, the clavicular head of SCM and a fat pad before scalenus anterior becomes visible.
Scalenus anterior is typically described as arising from the scalene tubercle of the first rib and inserting into the anterior tubercles of C3-6 (Bruce et al 1967, Drake et al 2005, Grant and Basmajian 1965, Last 1978, Moore and Dalley 2006, Standring 2005).
In order to further examine the position of scalenus anterior in the posterior triangle of the neck we dissected this region in a single embalmed cadaver (male, 64 years).
If the scalenus anticus muscle hypertrophies, the vein is then compressed and occludes.
Intermittent or partial obstruction should be treated by first rib removal through the transaxillary approach, with resection of the costoclavicular ligament medially, the first rib inferiorly, and the scalenus anticus muscle laterally.
If symptoms recurred, a first rib resection, with or without thrombectomy, was considered, as well as resection of the scalenus anticus muscle and removal of any other compressive element in the thoracic outlet, such as the costoclavicular ligament, cervical rib, or abnormal bands (55).
Some cover the end of the rib at the transverse process of the vertebra with scalenus medius muscle.