Triradiate cartilage

At a glance

English

Triradiate cartilage

Latin (TA2)

Cartilago triradiata

System

Cartilage

Region

Abdomen

Side

Paired, left and right

About the triradiate cartilage

The triradiate cartilage is the growth plate at the centre of the acetabulum in the developing hip bone. The hip bone begins as three separate bones, the ilium above, the ischium behind and below, and the pubis in front, and each contributes part of the socket for the head of the femur. Where they meet in the floor of the socket they are held together by a plate of cartilage with three limbs radiating from a common centre, so that seen from the side it looks like the letter Y. The Latin name cartilago ypsiloformis records the same shape.

Each limb of the Y lies between two of the bones: one between ilium and pubis, one between ilium and ischium, and one between ischium and pubis. Growth at these plates lets the acetabulum deepen and widen in step with the growing femoral head, so a normal socket depends on the cartilage working properly. Small secondary centres of ossification appear in and around it near puberty, including the os acetabuli at the pubic part of the rim.

The cartilage closes, and the three bones fuse into a single hip bone, at a bone age of about twelve years in girls and fourteen in boys. After closure the lines of fusion meet at the centre of the acetabulum, and the socket no longer grows in depth.

On a front-to-back X-ray of an infant's pelvis the cartilage shows as a gap in the acetabular floor. Hilgenreiner's line, drawn horizontally through both triradiate cartilages, and Perkin's line, dropped vertically from the outer edge of each socket roof, divide the hip into quadrants; the femoral head or its ossific centre should sit in the lower inner quadrant, and displacement suggests developmental dysplasia of the hip. Injury to the plate in childhood, for example from a pelvic fracture, can stop growth early and leave a shallow socket. Because its closure is a dependable marker of skeletal maturity, surgeons also check it when planning operations on the growing spine or hip.

Attachments and function

Attaches from

The edges of the ilium, ischium and pubis where they converge in the floor of the acetabulum.

Attaches to

Each limb joins the two neighbouring bones of the hip bone: ilium to pubis, ilium to ischium, and ischium to pubis.

Function

Serves as the growth plate of the acetabulum, allowing the socket to enlarge and deepen in step with the femoral head until the three bones fuse.

Blood supply

Supplied by vessels of the acetabular floor, mainly branches of the obturator artery and the deep branch of the medial circumflex femoral artery.