La Structure des Os Longs

Long Bone Structure

Introduction

Long bones are essential components of the skeletal system, providing support, stability, and protection to the body. They are formed during embryonic development and continue to grow and mature throughout childhood and adolescence. The structure of long bones is complex, involving a combination of bone, cartilage, and other tissues. In this article, we will explore the structure of long bones in detail, focusing on their formation, growth, and histological composition.

Formation and Growth

Long bones are formed through a process called ossification. This process begins with the differentiation of mesenchymal cells into chondrocytes, which produce a cartilage model of the future bony skeleton. Blood vessels on the edge of the cartilage model bring osteoblasts, which deposit a bony collar. Capillaries penetrate the cartilage and deposit bone inside the cartilage model, forming a primary ossification center. As the cartilage and chondrocytes continue to grow at the ends of the bone, the medullary cavity expands and remodels. After birth, this same sequence of events occurs in the epiphyseal regions, and each of these centers of activity is referred to as a secondary ossification center.

Histological Composition

Long bones are composed of both cortical bone (also known as compact bone) and cancellous bone (also known as trabecular bone). Cortical bone is a dense, hard tissue that surrounds the circumference of the bone and provides strength and support. Cancellous bone is a spongy, porous tissue found in the medullary cavity and acts as a reservoir for bone marrow and red and white blood cells.

Primary Ossification Center

The primary ossification center is the region where the initial mineralization of bone occurs. It is formed by the deposition of bone within the cartilage model, creating a solid bone structure. As the center grows, chondrocyte death and disintegration in the center of the structure allow for the invasion of blood vessels from the periosteum, which brings in osteogenic cells that become osteoblasts. These osteoblasts deposit more bone, eventually forming the primary ossification center.

Secondary Ossification Centers

Secondary ossification centers develop after birth in the epiphyseal regions. These centers are formed by the same process as the primary ossification center, with the formation of a cartilage model, invasion of blood vessels, and deposition of bone. As the child grows, the secondary ossification centers merge with the primary ossification center, gradually replacing the cartilage with bone. The cartilage remains at the epiphyses and at the joint surface as articular cartilage, providing a smooth surface for joint movement.

Epiphyseal Plate

The epiphyseal plate, also known as the growth plate, is the area of elongation in a long bone. It includes a layer of hyaline cartilage where ossification can continue. As the child grows, the epiphyseal plate lengthens, adding to the overall length of the bone. Eventually, the epiphyseal plate is replaced by bone, forming the epiphyseal line.

Bone Repair Materials

Bone repair materials play a crucial role in the treatment of bone defects. These materials can be derived from natural sources, such as autogenous bone and allogeneic bone, or synthetic materials, such as polymers and tissue-engineered bones. The choice of material depends on factors such as biocompatibility, biodegradability, porous three-dimensional structure, bone conduction, osteoinduction, and osteogenesis.

In conclusion, the structure of long bones is complex and involves a combination of bone, cartilage, and other tissues. The formation and growth of long bones occur through a process of ossification, with the development of primary and secondary ossification centers. The histological composition of long bones includes both cortical and cancellous bone, and the epiphyseal plate is the area of elongation. Bone repair materials are essential for the treatment of bone defects and can be derived from natural and synthetic sources. Understanding the structure and formation of long bones is crucial for the development of effective treatments and interventions for bone-related conditions.