What Is an Epiphyseal Line?

Sacral cartilage refers to the plate-shaped cartilage where the periphery of irregular and flat bones and the ends of long bones meet the backbone during human growth. The cartilage of the palate continues to divide and proliferate and ossify, making the bone lengthen and expand. The iliac cartilage of all bones in the whole body ceases to proliferate and ossify until about 16-20 years old, and the iliac cartilage disappears. From then on, the long bones no longer grow, and the irregular bones and flat bones no longer expand. When the epiphysis and the backbone merge into a whole bone Later, a line called the iliac line remained on the surface where the two joined. After the iliac line was formed, the length of the bone no longer increased. ^{[1] The} patellar cartilage can continue to proliferate and ossify, increasing the length of the bone. As the iliac cartilage ossifies in adulthood, a line-like mark is formed at the iliac cartilage, which is called the iliac line. ^[2]

Cartilage structure between epiphysis and metaphysis. ^[3]

Iliac cartilage injury

Patella cartilage injuries account for as much as 18% of all pediatric fractures. Any fracture involving the patellar cartilage can cause growth disorders, unequal limb lengths, and deformities. ^[4]

The patellar cartilage is at both ends of the long bone, and the secondary ossification center appears in it. The middle layer of zygomatic cartilage that surrounds the secondary ossification center stores a layer of cartilage embryo cell bands, which is connected with the bipolar differentiated boundary embryo cell bands of the metaphyseal cartilage growth disk, and together form a surrounding secondary bone. The chondrocyte proliferative layer grows in the fossilization center, so the bone around the secondary ossification center is continuously ossified, which makes the callus larger. The secondary ossification center in the sacral cartilage is circular when it begins to ossify. Because the ossification process around the sacral heart is uneven, it gradually becomes oval or elongated. In terms of Yin, the secondary ossification center is slower toward the joint side and the diaphyseal side, but protrudes or swells to the end of the bone, and the ossification is more active. As the secondary ossification center gradually increases, it also changes from a circular shape to a shape closer to its bone end. The eccentric primary ossification center is more active towards the other side. The ossification is slow, and the transverse bone plate is formed under the cartilage. The active ossification is a cartilage calcification zone. The initial subchondral transverse bone plate is scattered and short. When the patellar cartilage is completely ossified to form a bone end and the surface is covered with articular cartilage, the subchondral transverse bone plate forms a complete bone plate shell. ^[7]

The calcified band around the epiphysis was transformed into a transverse bone plate, and the transverse bone plate was incomplete to intact. These three different tissue structures can be distinguished on X-rays. The special sign is that the calcification zone around the epiphysis is thick and the image is blurred, and even appears as uneven waves, which shows that the osseochondral osteogenesis is very active. The incomplete small transverse bone plate under the cartilage has a smooth bony articular surface, but it is not dense; the bony articular surface seen by the X-ray of the complete bone plate and shell is thin, clear, smooth and dense. By carefully observing these three different images on X-rays, we can confirm the histological characteristics of cartilage osteogenesis represented by this sign, which is of great reference value for analyzing and confirming osteogenesis in cartilage caused by various reasons. ^[7]