Busy Bones

show/hide words to know

Chondroblasts: cell that make cartilage and help in bone healing after a break.

Hard callus: a hard bump that forms around a fracture when a bone is broken and healing.

Osteoclast: cells in your body that break down bone material in order to reshape it.

Phagocytes: cells that swallow up germs and other unwanted waste materials in the body.

Soft callus: a soft bump that forms around a fracture when a bone is broken and healing.

How Do Bones Heal?

What's happening inside your body when a bone is broken? Lets take a closer look at the step-by-step process your body goes through to heal a broken bone. You can begin by watching this short video that shows the different stages of bone healing. If you want learn more about bone repair we have included details of each step below the video.

Bone Healing and Repair Steps

broken arm


As soon as one of your bones break, your body springs into action to fix the injury. The time it takes for a bone to heal depends on a lot of things, such as the person's age and location of the break.

bone healing - blood clot

Within a couple hours, a blood clot forms around the break. Inside the blood clot, special cells called phagocytes begin cleaning bone fragments and killing any germs which might have gotten in around the break. Phagocytes are part of the immune system. The word phagocyte means 'cells that eat' in Greek, so these cells are named after the way they surround and destroy unwanted bacteria and material.


bone healing - soft callus

Next, a soft callus made mostly of collagen is created around the fracture by another special group of cells called chondroblasts. This stage can last anywhere from 4 days to 3 weeks.


bone healing - hard callus

A hard callus forms next as osteoblast cells create new bone, adding minerals to make it hard. This stage typically begins 2 weeks after the break, and ends somewhere between the 6th and 12th week.


bone healing - remodeling

Lastly, the bone is remodeled. Special cells called osteoclasts break down extra bone around the fracture until it's completely healed and returned to its original shape. Bone remodeling is a very slow process which can take anywhere from 3 to 9 years to complete!


Image credits:

Leg cast from WikiHow

View Citation


Bibliographic details:

  • Article: Bone Healing
  • Author(s): the Arizona Science Center
  • Site name: ASU - Ask A Biologist
  • Date published: February 1, 2011
  • Date accessed: September 18, 2020
  • Link: https://askabiologist.asu.edu/bone-healing

APA Style

the Arizona Science Center. (2011, February 01). Bone Healing. ASU - Ask A Biologist. Retrieved September 18, 2020 from https://askabiologist.asu.edu/bone-healing


Chicago Manual of Style

the Arizona Science Center. "Bone Healing". ASU - Ask A Biologist. 01 February, 2011. https://askabiologist.asu.edu/bone-healing

MLA 2017 Style

the Arizona Science Center. "Bone Healing". ASU - Ask A Biologist. 01 Feb 2011. ASU - Ask A Biologist, Web. 18 Sep 2020. https://askabiologist.asu.edu/bone-healing

What's going on under a cast as a bone heals?

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