Now, we're going to finish the last subject area of this lecture and that is the thoracic outlet.
Anatomists actually described this as the thoracic inlet but clinically, the thoracic outlet will
have the following boundaries. First is the manubrium. We see the manubrium right in through
here. The boundary would be its superior limit that we see right around here.
The next structure that contributes to the boundary would be the first rib. This will be
bilateral structures. So, if we follow the superior surface of the manubrium in either direction
out here laterally, we see the first rib on this side and then the first rib on the opposite side
contributing to the thoracic outlet. The last anatomic structure that contributes to the thoracic
outlet is the first thoracic vertebra. We see that labelled right here. In this area of the thoracic
outlet, we have scalene muscles. Anatomy is full of geometric configurations and so, here is yet
another one. This is called the interscalene triangle. The interscalene triangle is going to be
bounded anteriorly by the anterior scalene muscle that we see here attaching to the first rib
inferiorly. Next muscle that contributes to the inner scalene triangle is your middle scalene.
We see the middle scalene here running posterior to the anterior scalene and also attaching
to the first rib. The third boundary to this triangle as you might expect would be the base
of the triangle and that is the inner or the first rib between the anterior scalene muscle
and your middle scalene muscle. Within the interscalene triangle, we have some structural
contents. Here, we see brachial plexus elements and more specifically, we're looking at the area
of the inferior trunk of the brachial plexus. If we look on the opposite side, another content
of the interscalene triangle is the subclavian artery. So, it will pass through this triangle
between the anterior and middle scalene muscles. Now, we're going to identify another
structural component here and that is the subclavian vein. As we look in the illustration
here, we see the subclavian vein passing through the thoracic outlet. However, it will travel
over the superior aspect of rib one but it out lies anterior to the anterior scalene muscle.
Consequently, the subclavian vein lies outside of the interscalene triangle,
whereas the artery passes through the triangle.