What is the Spine?

Your spine is a long stack of bones called vertebrae, and it provides the structure and the strength of your back. Between the vertebrae are squishy pads called discs, which act like cushions or shock absorbers. Together, the bones and discs allow you to bend, twist, and stand tall. Your spine also protects one of the most important parts of your body: the spinal cord, a bundle of nerves that carries messages between your brain and the rest of you (Figure 1). Without your spine, you would not be able to stand, dance, or even keep your head up.

How Young Spines and Old Spines Differ

Why can kids often run and play all day, while grandparents sometimes struggle just to get out of a chair? The answer is that spines change over time. Young spines are flexible, springy, and often straighter. The discs are soft and full of water. Discs are made of a fluid-filled, gel-like substance (called the nucleus pulposus) surround by rings of soft fibers (called the annulus fibrosus). This makes them squishy and able to bounce back easily after jumping or twisting. Meanwhile, older spines can become stiffer or more curved. The bones may weaken, and the discs lose water and can break down and shrink [1]. This makes them less squishy and less flexible. Everyday movements like standing, bending, or lifting can become harder and sometimes painful.

It is not just age that matters. How much you exercise, what sports you play, how heavy your backpack is, and how long you sit can change how your spine develops over time. For example, children who sit for long periods often have more stress on their lower spines [2]. On the other hand, physical activity, like swimming or running, strengthens the muscles that support the spine and can help relieve back pain, improving quality of life [3].

The Problem With the “Average Spine”

Doctors and scientists want to understand how spines work. The problem is that, for a long time, they mostly studied just one “average” spine.

Imagine if every shoe store sold only one “average” size of shoes. Some people might fit into those shoes, but most would not. That is what happens when researchers rely on one standard spine. Doctors usually use tools and implants made for that average size, and they make decisions based on how the average spine behaves, not on how each person’s individual spine does. We know, however, that your spine, your friend’s spine, and your grandmother’s spine can all be very different [1]. If doctors only test treatments on an average spine, they may miss what really works best for each individual.

An Exciting Solution: Human Digital Twins

This is where technology can make a big difference. Scientists can now build digital twin of a person’s spine. A digital twin is a computer copy of a person’s spine that looks and behaves just like the real one.

Human digital twins can answer questions like: What happens to this specific spine when running, jumping, or lifting? How might an injury or disease affect a given individual’s spine? Which surgery method would work best for this person? Best of all, these questions can all be answered safely using a computer, with no risk to the patient. This means fewer surprises and better outcomes for real patients.

Consider two kids: Taylor likes to spend hours reading and often carries a heavy backpack, while Jesse loves playing basketball and doing cartwheels. Even though Taylor and Jesse are the same age, their spines grow and move differently. If both ever had back pain, their doctors would want to know exactly how their spines are unique. A digital twin lets doctors study Taylor’s spine and Jesse’s spine separately, instead of assuming they are the same. That way, doctors can choose the safest and smartest treatments for each of them.

How to Build and Use a Digital Twin

There are four main steps in building a digital twin of the human spine (Figure 2).

First, doctors take pictures of the real spine. They use computerized tomography (CT) scans (which show bones in detail) or magnetic resonance imaging (MRI) (which shows soft tissues like discs well) to capture the exact shape of the patient’s spine. These scans consist of a series of 2D medical images, called slices, acquired at different height, width, and depth positions in the spine.

Second, scientists use specialized software to stack the slices of 2D images, turning them into a 3D model—like creating a loaf of bread from its cut-up slices.

Third, since all parts of the spine behave differently, scientists teach the computer how each part should bend and stretch, or even how blood flows and nutrients travel through them.

Finally, to make sure the digital twin is realistic, researchers mimic different situations, like jumping. This is done by telling the computer how the spine should be moved to match the action of jumping. Then the computer solves a large series of mathematical equations to calculate how the spine behaves and responds to a jump landing. The simulation results are then compared with experiments on real spines or with movement tests done by volunteers.

Once a digital twin is ready, it can unlock much information about the real spine that doctors and scientists did not have before! With digital twins of the spine, scientists can identify which parts experience the highest loads, how each disc deforms, and how close various tissues in the spine are to being injured. For example, a digital twin of a basketball player’s spine can show how much stress is applied when they land from a slam dunk, to see if it is safe for them to do so. These models can also provide a risk assessment for your grandparent’s spine, seeing how likely it would be that they would damage and hurt their spine in a fall. This knowledge could allow doctors to know more specifically and more confidently whether a patient requires a certain type of treatment. Doctors can even test out surgeries, implants, or braces using the digital twin before trying them on a real person.

How Digital Twins Could Change Medicine

Digital twins could transform medicine by shifting healthcare from one-size-fits-all solutions to treatments that are tailored to each individual patient. Instead of relying on average body structure, doctors could use a digital twin of a person’s spine to understand how their specific body responds to movement, aging, injury, or surgery. This can all be done virtually before anything is done in real life, making healthcare safer and more effective.

With digital twins, doctors can compare different surgeries and select the one that fits each patient’s spine best, instead of using the same method for everyone. Engineers can design implants like screws, rods, or artificial discs and test them on thousands of digital spines representative of real people before using them on patients. Scientists can also study why some spines age faster and suggest exercises or habits to keep people healthy longer.

However, not all doctors are using digital twins yet. First, computers have limits and simulating an entire spine in detail can take a lot of computing power. Turning medical scans into a working model can take a very long time. Second, not everyone gets CT or MRI scans. Also, these images cannot show everything, like the tiny fibers inside the discs, so the data can be limited. Finally, researchers need to prove that digital twins behave the same way a real spine would so that doctors trust the results. This is no easy task!

Scientists are working hard to overcome these challenges. In the future, the process could be faster and easier, partly due to tools like artificial intelligence [5]. Excitingly, digital twins are being made for other parts of the human body too, including hearts, brains, lungs, and even entire bodies [5]!

One important lesson from all this: spines are supposed to be different. Your spine is not supposed to look or act exactly like anyone else’s, and it should not be treated as if it does. Digital twins make the differences between people visible and measurable by turning each person’s spine into a model that can be studied and tested. They help celebrate our differences by turning individual uniqueness into knowledge that doctors can use to make smarter and safer medical decisions tailored to each and every patient!

Glossary

Implant: ↑ A medical device placed inside the body to replace, support, or strengthen a body part, such as an artificial spinal disc or a screw used in spine surgery.

Digital Twin: ↑ A detailed computer model of a person’s body or body part that can be used to study how it moves, reacts to forces or changes over time.

Computed Tomography (CT): ↑ A scan that uses X-rays from many angles to create 3D pictures of the body, especially bones.

Magnetic Resonance Imaging (MRI): ↑ A scan that uses magnets and radio waves to make detailed pictures of soft parts inside the body, like muscles and discs.

Simulation: ↑ A computer test that shows how something would behave in real life, like how a spine bends.

Load: ↑ Forces or pressure placed on the body such as when standing, lifting, jumping, or carrying a heavy backpack.

Artificial Intelligence (AI): ↑ A type of computer program that can learn patterns and make smart decisions like a human.

Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

This work was funded by the European Union under the Marie Skłodowska-Curie Actions (MSCA) Doctoral Networks (Grant #101169278). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the MSCA. Neither the European Union nor the MSCA can be held responsible for them.

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The author(s) declared that generative AI was not used in the creation of this manuscript.

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