The angle of Louis is the eponymous name given to the sternal angle which is the palpable anatomical feature formed from the manubriosternal junction. The manubriosternal junction is the joint of the sternal body and the manubrium.
This angle of Louis is a synarthrosis, a type of joint characterized as a fibrous connection between two bones (the manubrium and the sternal body in the case of the angle of Louis) which does not allow any significant movement.
In a cadaveric study of preserved skeletal specimens, the sternal angle ranged from 149.0 degrees to 177.0 degrees with an average of 163.4 degrees in men and 165.0 degrees in women.
A small amount of movement in the angle of Louis does occur, particularly in younger people where the fibrous joint features increased flexibility. Complete fusion of the angle of Louis generally occurs at approximately 30 years of age. Using in-vivo spiral-CT data, the movement in the joint during forced breathing has been measured at approximately 4.4 degrees.