Beta angle (developmental dysplasia of the hip)
The beta angle is a measurement used in the ultrasonographic assessment of developmental dysplasia of the hip (DDH).
It is defined as the angle formed between the vertical cortex of the ilium and the triangular labral fibrocartilage (echogenic triangle) and thus reflects the femoral head cartilaginous coverage. There is a great deal of variability in the beta angle (much more than the alpha angle), and as such, it is not universally used.
In some instances, the beta angle is necessary to determine the subtype of hip dysplasia (e.g. type Ia vs. Ib, or type IIc vs. type D - see the sonographic classification of developmental dysplasia of the hip (DDH)). The cut off beta angle depends on type .
History and etymology
Reinhard Graf originally described both the beta angle and the alpha angle in 1980 .