What Is the Bone Collar?

In the middle part of the cartilage, osteoprogenitor cells in the perichondrium proliferate and differentiate into osteoblasts, which attach to the surface of the cartilage tissue to form a thin layer of primitive bone tissue.

In the middle part of the cartilage, osteoprogenitor cells in the perichondrium proliferate and differentiate into osteoblasts, which attach to the surface of the cartilage tissue to form a thin layer of primitive bone tissue.

Chinese name

Bone collar

Foreign name

bone collar

Department

orthopedics

Bone Collar Overview

The bone tissue is collar-shaped and surrounds the middle part of the cartilage embryo. After the bone collar is formed, the perichondrium on its surface is renamed the periosteum.

Osteochondral cartilage

1. Formation of cartilage embryos: Mesenchymal cells are dense and differentiate into bone progenitor cells at the site where long bones will occur, which in turn differentiates into chondrocytes. Chondrocytes secrete the cartilage matrix, and the cells are embedded in it, becoming cartilage tissue. The surrounding mesenchyme differentiates the perichondrium, so a hyaline cartilage is formed. Its shape is similar to the long bones to be formed, and is called a cartilage model.

2. Bone collar formation: After the formation of cartilage embryos, blood vessels appear in the perichondrium around the middle segment. Due to sufficient nutrition and oxygen supply, the osteoprogenitor cells in the deep layer of the perichondrium divide and differentiate into osteoblasts, and produce cartilage on the surface. Bone, osteoblasts themselves are also embedded in them to become bone cells. Osteoid calcification is a bone matrix, which forms a thin layer of bone cancellous that surrounds the middle part of the cartilage embryo, called the bone collar. The cartilage on the surface of the bone collar is renamed adventitia. The osteoprogenitor cells deep in the periosteum continue to differentiate into osteoblasts. New bone trabeculae are added to the surface of the bone collar and its two ends to gradually thicken the bone collar and extend from the middle part of the cartilage to both ends to gradually widen.

3. Formation of primary ossification center: After the formation of the bone collar, the chondrocytes in the middle part of the cartilage prototype of the bone collar are enlarged due to hypoxia, which degrades the internal cartilage tissue corresponding to the bone collar and secretes alkaline phosphatase, making it The surrounding cartilage matrix is calcified, and the hypertrophic chondrocytes degenerate and die. At the same time, the monocytes located in the blood vessels of the periosteum penetrate the blood vessels and fuse to form osteoclasts. The osteoclasts first dissolve the bone tissue of the bone collar. Subsequently, the osteoclasts together with the osteoblasts and bone progenitor cells in the periosteum And interstitial cells penetrate the bone collar and enter the degenerate cartilage area, osteoclasts decompose and absorb the calcified cartilage matrix, forming many tunnels with the long axis of the original backbone. Osteoblasts adhere to the surface of the remaining cartilage matrix to form bones, forming primitive trabeculae. This area is called the primary ossification center. The cavity of the tunnel is called the primary bone marrow cavity, and the cavity is filled with bone progenitor cells, osteoblasts, osteoclasts and hematopoietic tissues that are forming, collectively referred to as primary bone marrow.

After the formation of the primary ossification center, due to the continuous extension of the bone collar to both ends, the cartilage tissue degraded by hypoxia in the cartilage prototype also continuously expanded to both ends, and then the osteoclasts in the primary bone marrow cavity continued to destroy the absorbed and degraded cartilage matrix. Osteoblasts continued to expand to both ends, and the original bone trabeculae was soon broken down and absorbed by osteoclasts, causing many primary bone marrow cavities to fuse into a larger bone marrow cavity. The inner surface of the bone collar is gradually broken down and absorbed by osteoclasts, which makes the bone thicker while maintaining the proper thickness of the bone tissue, and allows the bone marrow cavity to expand laterally. Due to the continuous growth of cartilage at both ends of the cartilage tissue, the cartilage adjacent to the bone marrow cavity continues to degenerate, so that the ossification process of the primary ossification center can continue from the middle part of the backbone to both ends, and the bone marrow cavity also expands longitudinally along with it.

4. The emergence of secondary internalization centers and the formation of epiphyses: The time of appearance of secondary ossification centers varies from bone to bone, ranging from as early as before birth, to months or years after birth. It appears in the center of the cartilage at both ends of the shaft. The occurrence of secondary ossification centers is similar to that of primary ossification centers, but ossification proceeds from the center to the surroundings. Finally, most of the cartilage tissue was replaced with primary bone cancellous, and the two ends of the bone shaft were transformed into early callus. The patellar surface always retains a thin layer of cartilage, which is articular cartilage. There is also a certain thickness of cartilage layer between the epiphyseal and the diaphysis, which is called epiphyseal plate.