The sternal angle (also known as the angle of Lewis, angle of Louis, angle of Ludovic, or manubriosternal junction) is the projecting angle formed between the manubrium and body of a

sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...

at their junction at the manubriosternal joint. The sternal angle is a palpable and visible landmark in

surface anatomy Surface anatomy (also called superficial anatomy and visual anatomy) is the study of the external features of the body of an animal.Seeley (2003) chap.1 p.2 In Bird anatomy, birds, this is termed ''topography''. Surface anatomy deals with anatomi ...

, presenting as either a slight body ridge or depression upon the upper chest wall which corresponds to the underlying manubriosternal joint. The sternal angle is palpable and often visible in young people. The sternal angle corresponds to the level of the 2nd costal cartilage on either side, and the level between the fourth and fifth thoracic vertebra. The sternal angle is used to define the transverse thoracic plane which represents the imaginary boundary between the superior and inferior mediastinum. It is also used to identify the second rib during

physical examination In a physical examination, medical examination, clinical examination, or medical checkup, a medical practitioner examines a patient for any possible medical signs or symptoms of a Disease, medical condition. It generally consists of a series of ...

and then the rest of the ribs by counting.

Anatomy

The sternal angle forms an angle of about 162° in males.

Relations

It marks the approximate level of the 2nd pair of

costal cartilage Costal cartilage, also known as rib cartilage, are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, pr ...

s, (sources differ) the level of the

intervertebral disc An intervertebral disc (British English), also spelled intervertebral disk (American English), lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the ver ...

between

thoracic vertebra In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

T4-T5 or the lower border of the thoracic vertebra T4, and the space between the

spinous processes Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of thoracic vertebrae T3-T4. The horizontal plane that passes through the sternal angle and the articular disc between the 4th and 5th thoracic vertebrae represents the imaginary boundary between the superior mediastinum and inferior mediastinum. It is located approximately 7 cm inferior to the superior margin of the manubrium. The sternal angle is used in the definition of the

thoracic plane The mediastinum (from ;: mediastina) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is a region that contains vital organs and structures within the thorax, mainly the heart and its vessels, the es ...

. The angle also marks the level of a number of features: :* Boundary between the superior and inferior portion of the

mediastinum The mediastinum (from ;: mediastina) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is a region that contains vital organs and structures within the thorax, mainly the heart and its vessels, the eso ...

:* Passage of the thoracic duct from right to left behind esophagus :*

Tracheal bifurcation The carina of trachea (also: "tracheal carina") is a ridge of cartilage at the base of the trachea separating the openings of the left and right main bronchi. Structure The carina is a cartilaginous ridge separating the left and right main br ...

. The carina of the trachea is thus, present here. It is deep to the sternal angle. :* The bifurcation of the

pulmonary trunk A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and t ...

:* The superior limit of the

fibrous pericardium The pericardium (: pericardia), also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong inelastic connective tissue (fibrous pericardium), a ...

surrounding the

ascending aorta The ascending aorta (AAo) is a portion of the aorta commencing at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum. Structure It passes obliqu ...

:* Termination of the

azygos vein The azygos vein (from Ancient Greek ἄζυγος (ázugos), meaning 'unwedded' or 'unpaired') is a vein running up the right side of the thoracic vertebral column draining itself towards the superior vena cava. It connects the systems of superio ...

into the

superior vena cava The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart. It is a large-diameter (24 mm) short length vei ...

:* Ligamentum arteriosum :* Loop of left recurrent laryngeal nerve around aortic arch :* The beginning and end of the

aortic arch The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea. Structure The aorta begins ...

Clinical significance

The sternal angle is the most frequent site of

sternal fracture A sternal fracture is a bone fracture, fracture of the Human sternum, sternum (the breastbone), located in the center of the chest. The injury, which occurs in 5–8% of people who experience significant blunt chest trauma, may occur in vehicle a ...

among elderly people.

Surface anatomy and physical examination

The sternal angle marks the point at which the costal cartilage of either second rib articulates with the sternum. During

physical examinations Physical may refer to: *Physical examination In a physical examination, medical examination, clinical examination, or medical checkup, a medical practitioner examines a patient for any possible medical signs or symptoms of a Disease, medical co ...

, the readily palpated sternal angle is thus used as a landmark to identify the 2nd rib, and by extension, by counting, also the remaining ribs. Meanwhile, the first rib cannot be used for this purpose because it cannot be palpated. Counting ribs is essential attempting to make a thoracic incision; an incision at the first or second rib interspace can result in damage to large, important blood vessels and the brachial plexus. Identification of the second rib and thus the second intercostal space inferiorly is useful when auscultating heart sounds. The optimal location for auscultation of the aortic valve is generally the right second intercostal space, whereas the optimal location for auscultation of the pulmonic valve is generally the left second intercostal space. The sternal angle is used as the starting point in physical examinations of the heart since the sternal angle is located 5 cm superior to the right atrium.

History

The sternal angle is also called the angle of Louis, but the reason for that name was lost. Once thought to be after

Antoine Louis Antoine Louis () (13 February 1723 – 20 May 1792) was a French surgeon and physiologist. He was originally trained in medicine by his father, a sergeant major at a local military hospital. As a young man he moved to Paris, where he served as ' ...

Wilhelm Friedrich von Ludwig Wilhelm Frederick von Ludwig (16 September 1790 – 14 December 1865) was a German physician known for his 1836 publication on the condition now known as Ludwig's angina. Early life Ludwig was born in Uhlbach (near Stuttgart) in the state of Wür ...

, it is now believed to be after

Pierre Charles Alexandre Louis Pierre-Charles-Alexandre Louis (14 April 178722 August 1872) was a French physician, clinician and pathologist known for his studies on tuberculosis, typhoid fever, and pneumonia, but Louis's greatest contribution to medicine was the development ...

References

External links

* - "Thoracic Wall: Bones" {{DEFAULTSORT:Sternal Angle Bones of the thorax