Ever since she can remember, Penny's legs have been two different lengths.
Initially, the discrepancy was small enough to ignore, and later it could be fixed with shoe lifts.
But this difference only increased over time, and after years of difficulty walking and misalignments in posture, she's now dealing with scoliosis, alongside chronic back and joint pain.
Penny is far from the only person with this problem.
Differences in leg length can emerge for various reasons, from genetic and hormonal conditions to injuries that impact bone growth.
But while we still don't know exactly what degree of difference causes health issues, doctors have made great strides in figuring out how to even out these mismatched limbs.
To lengthen a bone, you need to grow new bone tissue.
And a great way to get the body to do that is to break an existing bone.
Within five to seven days of a bone break or fracture, the body will form a fracture callus at the damaged site.
Over several weeks this jelly-like blob of scab tissue will solidify into cartilage, which will harden into standard bone over two to three months.
But with the proper tools, surgeons can control and extend this process, using the fracture callus like a bone printer to extend a limb's length.
While doctors throughout the early 20th century attempted to nail pull, clamp and pin bones to guide this process.
A monumental breakthrough came in the 1950s from Soviet orthopedic surgeon Gavriil Ilyzadov.
He developed a technique called distraction osteogenesis, which begins with a controlled bone break called an osteotomy.
To do this, doctors cut a small nick in the skin, through which they cut the bone with a chisel-like tool.
Then, they hooked a kind of circular frame called an external fixator above and below the break.
The posable fixator allowed doctors to precisely pull the healing bone apart, and the device's modern-day descendants are still used for correcting complex bone deformities.
But since their wires and pins puncture the skin, they often pull on muscles, scar soft tissue and create opportunities for infection.
So, when possible, modern surgeons typically rely on a more recent breakthrough— implantable lengthening nails.
To see these in action, let's check back in with Penny.
Her right femur is five centimeters shorter than its counterpart.
To increase its length with an internal nail.
The surgeon first places rotation marker pins above and below the site of the eventual bone cut.
Then they perform an osteotomy and the surgeon threads the nail through the broken bone, securing it on both sides of the cut, before removing the rotation markers and closing the skin.
Once the fracture callus forms, the nail can get to work in one of several ways.
Some allow the patient to twist their leg back and forth to rotate gears along a track.
Others have a controller that can gradually extend the nail, either via a cord routed through the skin or wirelessly controlled magnets that rotate gears inside the nail.
In a given day, the bone is gradually lengthened several times, rarely exceeding one millimeter daily.
This slow speed is essential, both for bone formation and nearby soft tissue.
Since our bodies can't make new muscle or nerve cells, limb lengthening requires our existing cells to stretch.
And if they're stretched too quickly, it can lead to joint tightness or nerve pain.
Once the desired length is reached, the new bone is left to heal and solidify.
Like any surgery, bone lengthening has its risks and limitations.
In rare cases, implanted nails can break, requiring further surgery to remove or replace.
And when limb length differences are especially large, patients may require multiple surgeries.
But the biggest limitations are access and awareness.
Since this technology is new, the surgery can be expensive.
And many doctors and hospitals don't yet have the tools or expertise to perform lengthening surgeries.
But hopefully it won't take long for these surgeries to become accessible to people from all walks of life.
Do you ever feel like you don't know enough about your own body?
Subscribe to this channel to learn about everything from baldness to muscle growth, to why we have hair in such random places.
Stay tuned and stay curious!
