The vertical component of the "Y" is the meeting of the ischium and pubic bone. The anterior arm is the junction of the ilium and pubis. The posterior arm is the junction of the ilium and ischium.
The triradiate cartilage is a nonarticulating structure and constitutes approximately 30% of the acetabular cartilage complex. The acetabular articulating cartilage constitutes the remaining two thirds, with the triradiate cartilage at the periphery of the acetabulum, with the junction at the superior aspect of the acetabulum.
Closure or fusion of the triradiate cartilage occurs in mid-adolescence, typically by 15-16 years in males and 13-14 years in females, beginning at the acetabulum and finishing at the greater sciatic notch between ilium and ischium.