The beta angle is the second key measurement in the Graf method of neonatal hip ultrasound, complementing the alpha angle. While the alpha angle measures the bony acetabular roof, the beta angle measures the angle formed between the iliac bone line and the cartilaginous roof of the hip socket, reflecting the degree of cartilage coverage over the femoral head. A beta angle of less than 55 degrees is considered normal, indicating good cartilaginous coverage. A beta angle greater than 77 degrees suggests significant hip immaturity or instability. Together, the alpha and beta angles help classify infant hips into different categories of maturity and guide decisions about whether treatment is needed.
Sonography Term