August 26, 2022 – Healing a broken bone isn’t always a simple process of putting on a cast and waiting for the body to do its thing over time. The many materials that make up our bones have different densities and interact in different ways that affect whether a fracture will heal properly.
A fracture that does not heal properly is called a nonunion and can occur in long bones, such as a bone. B. a leg bone, lead to a disability. And doctors can’t always tell when a nonunion has occurred, let alone predict how likely it is in advance. But bone imaging research is on its way to changing that, giving doctors a glimpse into the future so they can spot problems earlier.
Mechanical engineering researchers at Lehigh University in Bethlehem, PA are using bone imaging and virtual mechanical testing to develop a more accurate model of the healing process.
A virtual model can help doctors see when a bone is deviating from a healthy healing process so they can intervene earlier. The key is to better understand the physical process in the healing zone where the fracture is actually repaired.
In the cast
The healing process begins when the body recognizes the break and sends out immune cells to trigger inflammation. Swelling is the body’s warning signal to stop using the injured part.
Blood cells also collect around the injury, and this mass of cells — a hematoma, or blood clot — fills the space at the fracture site. Over the next week, a type of soft bone called callus gradually replaces the blood clot and holds the bone together, although it’s not yet strong enough to begin using the bone. After a few weeks, the callus has time to harden, and then hard bone begins to replace the hard callus.
But it’s difficult to see how well these later stages show up on X-rays because hard callus and hard bone look so similar. Engineers are working to understand the mechanical properties of bone and callus, such as mass and density, so they can better predict when hard bone has completely replaced callus. Predicting too early could hinder the healing process if the person uses the bone normally before it has fully healed.
Previous computer models could not accurately distinguish hard callus from hard bone, mainly because callus itself is made up of different types of tissue with different physical properties.
But this new research relies on testing the stress placed on the bone during twisting. The researchers fed these test results and the corresponding CT images into a computer to model the healing process. Lighter areas in the image represent stiffer, harder bones, so their work helped investigators pinpoint the cutoff point where the material stops being callus and turns into bone. Knowing this threshold can help identify earlier when nonunion occurs, which in turn can help doctors better understand how and why the healing process is failing so they can help.