ERC Display mm vs X-Ray mm

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Joined: May 2023

Posted on Jul 21, 2023, 1:54 pm

#1

For those who have done LL or currently going through it. Has your lengthened mm amount that your ERC is displaying match your measured distracted gap shown on your x-ray?

If not, which do you think is more accurate? The x-ray measurement or ERC display?

I am not sure which one to believe. X-rays can be effected by angles, x-ray tech, knee flexion, etc
The ERC can be effected by gear skipping, both sides being lengthened accidentally etc.

I currently have a 5mm difference between the ERC display and x-ray measurement and I am not sure which one to believe.

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B

Body Builder

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Posted on Jul 21, 2023, 2:17 pm

#2

I used X rays with a ruler next to my feet and it was a very precise way to measure the bone gap, much better than the programs my doctor used (although the difference was ay max 2-3 mm). And the height I gained was exactly the same after my last x ray with the ruler

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V

Vx88x

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Posted on Jul 21, 2023, 2:23 pm

#3

Quote from: Body Builder on July 21, 2023, 02:17:17 PMI used X rays with a ruler next to my feet and it was a very precise way to measure the bone gap, much better than the programs my doctor used (although the difference was ay max 2-3 mm). And the height I gained was exactly the same after my last x ray with the ruler

So I would essentially place a metal ruler next to my femur as my x-ray is being taken?

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M

Maison

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Posted on Jul 21, 2023, 3:45 pm

#4

The ERC Display generally corresponds well with the actual nail lengthening amount, but it isn't flawless. If there's an issue with the equipment or a patient's operational error, the actual lengthening might vary slightly.

X-ray images are magnified more than the real object.
To correct this, we can use tools like a calibration ball or a ruler, or measure a nail diameter.
If an x-ray shows a nail's diameter as 11 mm, but it's really 10 mm, the image is 10% larger.

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V

Vx88x

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Posted on Jul 21, 2023, 7:00 pm

#5

Quote from: Maison on July 21, 2023, 03:45:12 PMThe ERC Display generally corresponds well with the actual nail lengthening amount, but it isn't flawless. If there's an issue with the equipment or a patient's operational error, the actual lengthening might vary slightly.

X-ray images are magnified more than the real object.
To correct this, we can use tools like a calibration ball or a ruler, or measure a nail diameter.
If an x-ray shows a nail's diameter as 11 mm, but it's really 10 mm, the image is 10% larger.

So if x-ray calibrated properly and the nail diameter is 11mm and the distraction gap says 70mm, the gap should be accurate technically?

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J

jerrytheman

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Posted on Jul 21, 2023, 7:24 pm

#6

if you're measuring it yourself, the scale on the x-ray is not accurate. It's because the placement marker they put is behind your leg and your femur is above that. Just have your surgeon measure it for you. But mine is not according to scale ever.

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M

Maison

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Posted on Jul 21, 2023, 11:23 pm

#7

Quote from: Vx88x on July 21, 2023, 07:00:11 PMSo if x-ray calibrated properly and the nail diameter is 11mm and the distraction gap says 70mm, the gap should be accurate technically?

Yes.
For example, if the actual diameter of the nail is 10mm and its diameter on the X-ray is 11mm, this means the X-ray image magnifies the actual size by 1.1 times.
Therefore, if the lengthening gap on the X-ray is 77mm, the actual lengthening amount is 70mm, calculated as 77/1.1
The surgeon can also use measurement software with a calibration function, as you have mentioned.

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M

Maison

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Posted on Jul 21, 2023, 11:41 pm

#8

Quote from: jerrytheman on July 21, 2023, 07:24:16 PMif you're measuring it yourself, the scale on the x-ray is not accurate. It's because the placement marker they put is behind your leg and your femur is above that. Just have your surgeon measure it for you. But mine is not according to scale ever.

As you pointed out, the method of using a ruler can sometimes be inaccurate.

When a radiologic technologist places a ruler or a calibration ball near the film, it's important to keep it the same distance as the bone to the film.
This method can be hard and not always exact.
But if there's a nail, measuring with it is the best way.

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N

Nitro1

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Joined: Jan 2024

Posted on Jan 3, 2024, 6:34 pm

#9

Did you resolve this?

I’m having the same issue

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