It evolved in the 90s when we started using devices that were inside the bone instead of outside the bone. Many of those devices had mechanisms to expand. In other words, you will drill the bone to create a hollow space and then you will insert one of these telescopic rods into the bone. These telescopic rods have a mechanism and that mechanism can be activated mechanically, electronically or magnetically. And initially these mechanisms were crude and, in fact, the process was painful. And actually, by the name of PRECICE nail, they named it that because it was one of the first very ‘precise’ ways to make the bone as long as you wanted. Early equipment was weak, meaning they were not strong enough for you to put your full weight on them. After implementation you slowly start lengthening the bone one millimeter per day. This is typically the rate at which bone can maintain by forming new bone and soft tissue can regenerate new muscles, nerves, arteries, skin, etc. It was Ilizarov’s work that introduced it. They did this experimentally: fast, slowly, figuring out what the ideal rate was for legs to lengthen in animals – and then of course in thousands and thousands of humans since then.
For myself, oh my God, I have lengthened more than 25,000 limbs in my career so far. So we also have a lot of experience to see what rates and what works best for people so that they don’t have pain and they can regenerate the bones. You go too fast, you actually get failure in formation, you get a lot of complications, and if you go too slow, the bone actually heals prematurely and you can’t live as long because the bone is too strong.
And now the latest development, the PMX, is strong enough to allow full weight bearing, like the full weight of the patient. They will have pain after surgery and use a walking aid for a few days. They usually have no pain within two to three weeks and once the pain from the surgery goes away, they can walk without a walking aid. And this is a big new deal. The PRECICE 2, which was the predecessor to the PMax, could only support between 50 and 75 pounds of weight each time it took a step. So most people weigh more than 50 to 75 pounds. So this means you’ll have to use a walker or crutches for a long time, often about five months (until the new bone has healed and become as strong as normal). We let him start doing impactful things like running, jogging about five months after the surgery.
How do you control how much you stretch at a time?
So you have a machine on the outside, and it’s a remote-controlled machine with a magnetic device. There is a magnet inside the PMX, and the external device is about six inches by a foot long. Patients are trained to use it and stretch themselves four times a day at home. They put this big block on top of their foot, they press some buttons, and it lengthens inside. It is such a small quantity that every time it becomes so long that the actual length is not known and this is a big misconception. People have this perception about limb lengthening that you’re stretching and that’s the painful part. The actual rod, which is one-25th of an inch long, is invisible. What may be uncomfortable for patients or that patients often talk about is the stretching of the soft tissues along with the bone, which occurs gradually over several months.
