Beta angle (DDH)
The beta angle used in ultrasonographic assessment of developmental dysplasia of hip (DDH).
It is defined as the angle formed between the vertical cortex of the ilium and the triangular labral fibrocartilage (echogenic triangle). 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.
It is however necessary to determine, in some instances, the subtype of hip (e.g. type Ia vs Ib, or type IIc vs type D - see sonographic classification of developmental dysplasia of the hip (DDH) ) and the cut off beta angle depends on the type.
Both the beta angle and the alpha angle were originally described by Graf in 1980 1.
