Body processes

Ossification – Function, Task & Diseases


The medical term ossification refers to the growth of bones, also known as bone formation . A synonym is ossification . It is the formation of bone tissue during the growth phase and in the callus (scar tissue to bridge the fracture gap) in the secondary fracture healing in broken bones .

What is ossification?

Doctors distinguish between two types of bone formation. In desmal ossification , the bone is formed from the connective tissue , in chondral ossification , the bone is formed from an already existing cartilage .

In a normal course, ossification is a natural process of bone formation, which builds up the not yet fully formed skeleton , especially in childhood. If it progresses abnormally, increased bone formation occurs. Bones arise where they are not intended.

function & task

The bones develop either from the connective tissue (desmal, skull bones, clavicles ) or from the cartilage precursor (perichondral ossification). During the growth phase, bones form at the border between the metaphysis (longitudinal growth) and the epiphysis (growth area of ​​the long bones).

In adult humans, bones are regularly renewed through the activity of osteoblasts (bone-forming cells) and osteoclasts (bone-breaking cells).

Ossification occurs as a result of an acquired (surgery, accident, injury) or congenital (autosomal inherited dwarfism) malformation of the skeleton due to impaired bone formation. Overstrained muscles and metabolic dysregulation can also be a cause. Sometimes ossification occurs ideopathically (without reason). It arises in the cartilaginous epiphyseal plates, which form the center of endochondral ossification.

The bones of the human skeleton are formed in different shapes. There are elongated tubular bones. Its head is called the epiphysis, the transition to the actual tubular shape is called the metaphysis. The tube as such is called the diaphysis. Typical representatives of this type of bone are the upper arm bones ( humerus ) and the thigh bones (femur). The skull bones are flat. A third type of bone is formed by the rounded sesamoid bones ( kneecap , hand bones). The air-filled bones are the bones of the facial skeleton such as the paranasal sinuses .

Each bone is surrounded by a fine periosteum . Inside there is a dense bone structure (compacta, corticalis), which gives strength to the bone. Uniformly aligned fibers reinforce the fabric. Bones are made up of organic collagen in the form of protein , bone and fat marrow, water, phosphate, and calcium .

Between the bone tissue are the osteoblasts and osteoclasts in the form of small cells. The osteoblasts are connected to each other by fine channels and produce the bone substance. The osteoclasts, as opponents, break down the bones again. The uniformly arranged lamellar bones are responsible for the typical bone structure.

If there is a fracture, a woven bone with fibers forms without any structure, which grows haphazardly. Only with the healing process does a structured, stable lamellar bone develop again.

Desmal ossification develops from the connective tissue formed from mesenchymal cells. In bone growth, the cells lie close together and are well supplied with blood. The mesenchymal cells are stimulated into osteoblasts, which produce new bone. Further osteoblasts accumulate on these new, very small bones, which also form bone material, so that the bone grows appositionally through accumulation. Skull bones typically form through this desmal process of bone growth.

In chondral ossification, bones are created as cartilage in the first step. Only in the course of this indirect (enchondral) ossification does the bone form from the cartilage material. From around the age of 19, perichondral bone growth is complete. The cartilage cells become larger and calcify and the osteoblasts enter the process at this point and act as anabolic cells for bone growth.

Diseases & Ailments

Medicine distinguishes between diseases that affect regular ossification and diseases that cause excessive ossification. In patients with achondroplasia ( dwarfism of the bones ), the long bones grow in width instead of in length, since the bone growth leads to premature closure of the epiphyseal plates. The cartilage cells become larger and calcify. Since there are no more cartilage cells in the affected bone, it cannot grow in length. Vertebrae, ribs and skull bones are not affected by achondroplasia, so these bones develop normally, but appear larger than they are in comparison to the shortened extremities. 

In heterotopic ossification, areas where connective tissue normally resides become ossified. The medical term heterotopic in this process means “occurring at a different location”. The tissue damage gives the body false reports and causes it to produce messenger substances that lead to ossification of cartilage tissue.

Larger bones that are affected by excessive ossification cause problems in the mechanical movement. The range of motion of the affected joints is significantly restricted. Minor new bone formations usually do not cause any problems because they are too minor.

Bone fractures are the most common cause of this irregular bone growth. The more complicated the fractures, the greater the possibility of ossification. Patients with multiple injuries are more likely to show excessive ossification than patients with a single injury. Hip replacement patients, for example, are affected more often than people with shoulder surgery. Bruises and infections can favor the course of excessive ossification. A basic prevention is not known. The orthopedic treatment begins with the axis deviations.

A lack of vitamin D in newborns significantly impairs normal bone formation. Rickets is the most common ossification disorder in newborns. An undersupply of vitamin D automatically leads to calcium deficiency . Since the bones consist largely of calcium, this deficiency leads to impaired bone growth. Newborns are therefore often given vitamin D.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.