“Once both sections of bone are connected again, specialised cells called osteoblasts produce bone cells”
SCIENCE
Bone fracture healing process Learn how your body mends broken bones If a bone has too much pressure put on it, there is a chance it will break. Your body has ways of repairing these breaks, but it takes time and care. There are different kinds of break, ranging from a hairline fracture to a fully shattered bone, but they all mend in a similar way. As a bone breaks, the blood vessels are also severed. Blood leaks out and forms a clot called a fracture haematoma. This stops blood flow to the area and also helps keep both pieces of bone aligned, ready for healing. The body then makes fibrous cells and cartilage, which reinforce the bond and strengthen it. This creates a callus, which is essentially a weakened bone. Over time, the callus builds up and the two parts of the bone
gradually fuse together, like a bridge being constructed from either side of a river until both ends meet in the middle. Once both sections of bone are connected again, specialised cells called osteoblasts enter to produce bone cells. These new cells replace the callus, returning the bone to its original shape. Much like repairing a broken toy with glue, the bone needs to be kept straight and steady for the fusion to happen correctly. This is why doctors will put a cast on the broken bone. The cast provides essential support, protection and stability, ensuring the broken bone doesn’t move. A cast will generally stay on for a few weeks until the bond has become strong enough, but it could take months for a properly set bone to fully recover.
All-star cast Most breaks on an arm or a leg will have a plaster cast put on them to prevent the bone from setting at a wonky angle or not setting at all. It will generally be made from plaster of Paris. This is a mixture of water and gypsum that sets really hard once it has dried. The broken bone is bandaged and the wet mixture is applied to the gauze. Once it has dried then it should provide safety and stability for the bone. Fibreglass is an increasingly common cast material. As with the plaster cast, the broken bone is bandaged up. Next, another bandage, made of fibreglass and layered with resin, is soaked in water. This makes it flexible enough to be wrapped around the bone before it hardens as it dries. This is much lighter than a plaster cast and the outer layer is waterproof.
The stages of bone repair Marrow Internal callus (fibrous tissue and cartilage)
New blood vessels
Healed fracture
Hard bone callus
Ruptured blood vessels External callus
Blood flow improves
Blood clot
Tissue growth
Remodelling
When a bone breaks, the blood vessels that run through the bone are severed. The blood forms a clot to align the bones. This creates a solid yet weak structure to prepare for mending. The clot also cuts off blood flow to the edges of the broken bone, so these cells die.
A few days later, the blood clot – called the fracture haematoma – is gradually replaced by tougher tissue, which becomes a soft callus. Fibrous tissue and cartilage are produced that begin to bridge the gap between the fractured ends. New blood vessels begin to form and the callus usually lasts around three weeks.
Bone-forming cells called osteoblasts work in teams to build a new bone, creating a more solid structure called a hard bone callus. It takes several months to fill the cavity with harder bone, strengthened by nutrients like calcium and phosphorus. However, it may take longer for the bone to be completely healed.
052 | How It Works
WWW.HOWITWORKSDAILY.COM
© Thinkstock
Blood clot forms
