The Sternal Angle


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Anatomy Odyssey and the Sternal Angle

The sternal angle is also called the Angle of Louis or the manubriosternal joint. It is found on the sternum between the manubrium (the upper part of the sternum) and the 10cm long sternal body as a  transverse ridge.




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In the lecture it was said that the sternal angle is one of the most prominent surface landmarks in the thorax, however, I would probably disagree as in my experience I find it much harder to identify the sternal angle than the more obvious landmarks such as the suprasternal notch (the dip in the collarbone at the top of the sternum)

If you need any help identifying the sternal angle, it can  be palpated 5cm below the suprasternal notch, where the sternal body meets the manubrium at an angle of 15 degrees.

Joint type: the sternal angle is a secondary cartilaginous joint, also known as a symphysis joint. (https://clinanat.com/mtd/282-sternal-angle-of-louis). This basically means it is made up of a plate of fibrocartilage connected to the articular hyaline surfaces of the bone.
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The joint varies with age: in young children it is made up of fibrous and elastic tissue, whereas in the elderly ossification may occur joining the joint.


Relations:
The sternal angle is a useful landmark in the thorax, as it can be used as a reference point for key anatomical structures in the area. An easy way to remember the important structures that passes behind the sternal angle is the mneumonic: RAT PLLANT. N.B. this mnemonic does not describe the structures in order of appearance, and is just to remember the structures in no particular order. 


RAT PLLANT
R = rib (the second rib)
A = aortic arch – the beginning and end of the aortic arch is found on this plane
T = tracheal bifurcation – where the trachea divides into left and right
P = Pulmonary trunk
L = ligamentum arteriosum
L = left recurrent laryngeal
A = azygos vein
N = nerves
T = thoracic duct  


Surface anatomy: The Angle of Louis is found 5cm below suprasternal notch
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The angle is at the level of the second costal cartilage
It is found between T4 and T5 vertebra posteriorly (http://medchrome.com/basic-science/anatomy/sternal-angle-of-louis-significance-of-landmark/) - the body of the sternum is opposite T5 to T8.


Clinical relevance:

•   -       The second rib is found at the level of the thoracic plane, this can be used as a reference point when finding the valves of the heart.
•   -       If the left recurrent laryngeal is damaged the patient will present with a hoarse voice
•   -       The sternal angle separates the mediastinum into superior and inferior parts – an important point to note is that the terminology is slightly different in radiology, and to not get confused by this in clinics


-->  The  Superior Mediastinum extends from the thoracic inlet to T4

 --> The Posterior Mediastinum extends from T4 to the diaphragm, an
http://thegoofyanatomist.weebly.com/uploads/3/0/9/9/30995885/3218989_orig.jpg
d can be divided into anterior, middle and posterior parts. The anterior mediastinum is below the sternal angle and in front of the heart, whereas the middle mediastinum contains the heart and the bronchi.

 --> The sternum is normally protected from injury by the presence of the elastic costal cartilages, but it may be fractured with dislocation of the thoracic spine.

Interesting fact from the sternal angle lecture
You can get a stab wound through bone – this surprised me, but was used as an example in the sternal angle lecture to demonstrate what structures lie behind the sternal angle, and could be at risk if you get stabbed at this point, for example, the arch of the aorta, the azygos system etc. We then talked about the consequences of a stab wound through bone for a while in more general terms, and the complications that can arise from a bone stab wound. These include…

- Osteomyelitis
https://www.wpclipart.com/cartoon/assorted/more_cartoons/bone_cartoon.png
- Bleeding – each bone has a score for how much fluid is lost, for example, a femur fracture requires a lot of fluid replacement as a significant volume of fluid is lost in this case. There is a debate in the literature about whether to give fluids first or to manage bleeding. This is because giving fluids carries similar risks to organ transplantation, and can destabilise the patient
- Shattered bone (in the humerus this could impinge on nerves such as the radial nerve)
- Bone necrosis (- by impinging on blood supply, as is the case for the scaphoid bone
- Fat embolism

History:
The sternal angle was named after the French physician, Antoine Louis

References:
http://anatomyzone.com/tutorials/musculoskeletal/sternal-angle/
http://medchrome.com/basic-science/anatomy/sternal-angle-of-louis-significance-of-landmark/
Gray's Anatomy
Teaching from the Anatomy Summer School

 Rat Image - https://s-media-cache-ak0.pinimg.com/originals/2d/1f/b8/2d1fb82a184c5b72d4a04f36277dd82b.jpg

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