How Orthopedic Surgeons Fix Bones - Part 1
⌚️ read time: 6 minutes
Have you ever wondered how a surgeon fixes broken bones?
Or if you’ve seen x-rays of fixed bones (or even had the surgery yourself), is it confusing to see all those screws and plates? In some cases, it can look like a hardware store gone wrong!
Well, today I’d like to walk you through how orthopedic surgery works.
Two x-ray views of the same forearm fixed with a plate and screws. There is one plate and six screws in both the radius and ulna.
How bones heal
I’m going to work to keep this as simple as possible. Apologies if I get too technical — feel free to comment below if anything is unclear.
In general terms, bones can heal in two different ways after they break. Conveniently, these two mechanisms are called ‘primary’ bone healing and ‘secondary’ bone healing.
As we’ll discover below, the difference lies in how close the bone ends are to one another after they break. Meaning, are they still connected, or are they resting apart? This is the main determinant of how the bone will heal. And an orthopedic surgeon must have a plan for which type of bone healing they are going to use to their advantage.
Primary bone healing
Today’s article is going to be about primary bone healing. We will get to secondary bone healing in a future article.
In primary bone healing, the ends of the bones are still touching and are very stable.
In fact, the bone ends have to be within 200 microns of each other (a micron is 1/1000th of a millimeter) and there has to be essentially no motion at the healing site.
So imagine your favorite puzzle. When putting the pieces together, the pieces would have to be compressed together and held without motion to achieve this type of healing.
How surgery achieves primary bone healing
If this sounds difficult to achieve, then congratulations, you’re paying attention! The above conditions to meet primary bone healing are very demanding, and they basically only occur with the help of surgery. If you’ve ever had a cast or a brace for a fracture, this is not the type of healing your body used…there’s just no way for a cast or a brace to give your bones the stability needed for primary healing.
Primary bone healing works best when there is a single break across a bone (meaning, it didn’t shatter into pieces). When this occurs, we can take that crack, line it up, and squish it back together.
This is where the cool stuff comes in.
To achieve the stability and squish that we need to achieve primary bone healing, we use our orthopedic tools to achieve compression at the fracture site. This is absolutely crucial for primary bone healing.
Let me show you how we do that with plates and screws.
The big toolbox
Below is a cartoon I drew of a typical fracture. Most broken bones break in some sort of diagonal or spiral pattern, depending on the specific forces that the bone was subject to before it snapped.
To achieve compression, we line those fracture ends up and put a plate on top, centering it over the fracture site (the image below shows a 7-hole plate).
Simple so far, right? Here’s where the technology gets cool.
For the image below, I’ve now turned the cartoon 90 degrees. So we’re looking at the bone from the side, with the plate on top.
On one side of the fracture, we place a screw in the plate. This essentially just holds the plate down to the bone for stability. Nothing too fancy yet.
Then, on the other side of the fracture, we place another screw. But this screw is the magic screw. We drill the hole for this screw as far as possible away from the fracture site, but obviously still within the oval-shaped hole of the plate.
If you notice, the oval-shaped holes actually have a little slope to them (dashed lines above). This slope is everything, keep it in your mind. Up top, the holes are flared out. Down at the bone surface, they have tapered inwards.
So, if you insert the screw as far away from the fracture as possible, as you tighten it down, the head of the screw will eventually contact the side of the oval hole.
Initially, it’s just contact. But as you tighten the screw more, it will ride down that slope. That screw is headed down into the hole you drilled for it, so it’s on a mission. As it rides down that slope, it will essentially push the plate out of its way (image below).
And because you put that anchoring screw on the other side of the fracture? The movement of the plate being pushed out of the way by the screw will now compress the fracture site down to that magical 200-micron squish that we know we need for primary bone healing.
Voila. Isn’t it beautiful?
The real-life result
Let’s return to our original x-ray.
As you can see below, there are three screws on each side of the radius fracture (fracture in red on the right). This helps provide long-term stability so the entire construct isn’t just relying on one or two screws.
If you really look, even though this plate and screw construct looks fairly symmetric, you can usually pick out the magic screw (in yellow above), the one that is slightly off-center within its oval-shaped hole (notice the teal gaps above are different). That’s the screw doing all the compression work!
The bone healing process then usually plays out over the course of about 6-10 weeks after surgery.
And the most counter-intuitive part of it all? All that work is done to support the bone while it heals. This means that as soon as the bone heals, all that hardware becomes completely irrelevant.
Most of the time it stays in the body for life…because who wants to have surgery all over again just to take it out? But it’s irrelevant and does no further good for the body after that initial window of healing.
Seems like a lot of work for a short period of time!
Different surgical options for primary bone healing
In reality, there are a couple other ways to achieve bony compression in the operating room. Depending on the fracture pattern and location, it can sometimes be achieved with a single screw, rather than a plate plus screws.
This can be done either in the way we drill for the screw:
Lag screw: intentionally drilling a wider drill hole on the near side of the bone and a smaller one on the far side will cause compression once the inserted screw engages the far side
Headless compression screw (image below): the screw is designed with threads of different sizes on the same screw, which will thus cause compression as it’s inserted
Takeaways:
Fractured bones can heal in different ways, depending on the characteristics of the break and how stable they are as they heal
Orthopedic surgeons need to know which type of bone healing they want to achieve when designing an implant to fix the fracture
Primary bone healing requires compression at the fracture site,which can be achieved with compression plating, lag screws, or headless compression screws.
I hope you enjoyed this peek behind the curtain! These are some of the decisions we make each day when faced with getting broken bones to heal.
Next time your friend tells you they had surgery for a broken bone, maybe you’ll take a look at the x-rays and be able to tell just how the surgeon did it. How’s that for a cocktail party trick?
