How do broken bones heal?

The bones are the strongest parts of the human body, but bones do break. How does a broken bone actually grow back together?

The bones are the strongest parts of the human body, but bones do break. How does a broken bone actually grow back together?

Although bone tissue is four times stronger than concrete, most people have the misfortune of breaking one or more bones at some point in their lives.

When a patient with a broken bone comes to the emergency room, they start by taking an X-ray so that the doctor can see exactly where the fracture is.

Next, you have to align the bone ends exactly right. In this way, the doctor ensures that the body needs to generate as little new tissue as possible and that the fracture heals properly.

The offenders were held to justice

The fractures must now be held in exactly the right position while the fracture is healing. This is usually done with a plaster cast and sometimes with a splint, which both provides support and reduces pain, as the bone ends can no longer move and thereby damage the surrounding tissue or nerves.

In complex cases, it is necessary to fix the bone ends, for example with metal threads, nails or screws, but this requires surgery.

The rule of thumb is that it takes twice as long for bones in the lower body to heal (16 weeks) than in the upper body (8 weeks). Children’s bones usually heal in half this time, but in older people, the bones need more time to heal together.

The cut is bleeding

If you break a bone, weeks or months in a cast usually follow. When the bone heals, however, the fracture site is often the strongest part of the bone. Below is an explanation of how the body rebuilds a broken bone.

1. Blood flows into the fracture surface

When a bone breaks, many blood vessels break and blood collects between the broken ends.

2. Stem cells build new bone tissue

So-called bone stem cells now arrive and start building new bone tissue. At the same time, blood vessels grow back together through the fracture.

3. The blood clot forms cartilage

The bone stem cells form cartilage tissue, which absorbs calcium salts and gradually hardens over several months.

4. The bone is whole again

After a few months, the bone is completely healed. During the healing process, the damaged bone has been kept immobile and this has resulted in the bone weakening – except for the newly formed bone tissue.

Bones need stress

Bones break down and rebuild themselves when stressed. As early as the 19th century, the German anatomist Julius Wolff discovered that bones become stronger the greater the load on them.

On the left is normal bone and on the right is porous and weak bone.

On the other hand, the bones become more porous and weaker when they are not subjected to stress. This can be seen, for example, in spaceships that stay in weightlessness for a long time.

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