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[Dragonheart]

Hi,
I’ve been reviewing information about various LL clinics with affordable prices and was considering Turkish ones. They quite often prefer to do Femurs as it allows to gain more height – 8 to 10cm. However, as an engineer I’m bothered with one question.

While tibia is perpendicular to the ground and leg overall, femur has this Q angle that technically positions it diagonally from outer side of your leg going to inner one (from top to bottom). Femur lengthening over nail (both LON or precise) is performed over your anatomical axis. It means that if you simply lengthen the femur bone, the more you lengthen it, the more it forwards “inside” to inner space between your legs. In other words – making your knees to be closer and breaking the mechanical angle.

To represent it visually I prepared a picture with comparison that I made myself.

 First comparison shows shift in mechanical angle, second one compares space between legs from pre-surgery to after-surgery, last one is same as second one but vice-versa.

I thought that maybe there’s a way in which doctors fix this mess by using a nail that is not fully straight for example, but found some articles and researches saying that there’s 1* angle change by each 1 cm of lengthening. And while natural angle is 6 degrees you can calculate how it is changed by lengthening femurs for 8cm.
Article 1: The effect on mechanical axis deviation of femoral lengthening with an intramedullary telescopic nail
Article 2: Effect of lengthening along the anatomical axis of the femur and its clinical impact

Now, can anyone explain why am I not seeing such information anywhere and not hearing others to speak about it loud? Does patients just prefer height over straight legs with healthy knees? I even wrote to couple of doctors directly, but they replied that 1) yes, they lengthen over anatomical axis 2) no, somehow magically mechanical axis is not changed (no proves ofc.)

I’d like to hear others opinions as I want to decide for myself if Femur is a no go and I should chose tibia no matter what or there’re clinics that do lengthening and correct the angle/axis to be the same by adding small curve (bend) to the segment of bone that gets extended. I do not trust doctors anymore (at least turkish ones) as it looks like they just want money and will blindly claim that everything will be great without any details or explanations.

Thanks!

[heightiseverything]

 Bump. This needs to be adressed.

[Body Builder]

Nice.
This is for someones who believe that 8-10 cm in femurs is a piece of cske while they swear that everyrhing more than 5cm on tibias will ruin your legs.
I never understood why even some doctors like Betz, who have good reputation (I don't know why) let their patients do some crazy amounts like 10-12 cm on femurs and most of them ended up with terrible knee pain etc. These pictures explain a lot.

So, of course femur LL is not safer than tibia one. Easier maybe (with internals only of.course) but no way safer in the long run.

[AnotherLLer]

What about lengthening up to 5 cm? Or up to 6.5 cm? Of course 10 cm is too much and it might produce visible changes in femur curvature but at least with conservative amount of lengthening, the mechanical axis won't deviate that much.

I'm too worried about this issue as I want to lengthen my femurs first since they're quite short and lengthening my tibia only for 5 or even 6 cm won't do that much for my starting height of 165 cm. I want to lengthen at least 6.5 cm on my femurs and at least 5 cm on my tibia for meaningful height gain of 11.5 cm and get long legs. Without doing femur and only doing tibia, I won't look good and the height gain won't be enough.

[lucindaris]

There are atleast 4 people on this forum with proven 11/12 cm femur. It takes much more time to recover for sure, but still noone of them had problems like some people in Turkey after 5-6 cm. I think it's just the best way if you want to have one surgery in your life and foreget about everything + you want to be quite mobile during the lengthening.

[AnotherLLer]

There's no way you can get away without doing tibia too after you lengthen past 5 or 6.5 cm on femurs, it will just look very bad when nked and biomechanics will be ruined too.

IMO, for most people who have about 0.80 tib/femur ratio, the best split is something like 6.5 cm on femur and 5 cm on tibia or 8 cm on femur and 6 cm on tibia if one needs to lengthen within the maximum possible safe limits. Minimum is 5 on femur and 4 on tibia to be worthwhile but 6.5 / 5 split is decent and lies in the middle of conservative and upper safe limits. 11.5 cm is half a head (assuming 23 cm is average head length of males) so 50% head length increase is a significant height increase IMO.

[Body Builder]

There are atleast 4 people on this forum with proven 11/12 cm femur. It takes much more time to recover for sure, but still noone of them had problems like some people in Turkey after 5-6 cm. I think it's just the best way if you want to have one surgery in your life and foreget about everything + you want to be quite mobile during the lengthening.

11-12cm are never the best way. Sooner or later you are going to have problems, epsecially knee pain.
Tall who did 11cm with Betz after a few years had terrible knee pain and did tibia LL also (while he didn't want as he was almost 1.90 after femur LL) trying to restore some of the femur-tibia ratio and fix his pain, I don't know if he made it though after tibia LL.
And also with 11-12 cm on femurs you'll look terrible.
So your advice is pure catastrophical. Noone should ever go for more than 8cm.

[heightiseverything]

11-12cm are never the best way. Sooner or later you are going to have problems, epsecially knee pain.
Tall who did 11cm with Betz after a few years had terrible knee pain and did tibia LL also (while he didn't want as he was almost 1.90 after femur LL) trying to restore some of the femur-tibia ratio and fix his pain, I don't know if he made it though after tibia LL.
And also with 11-12 cm on femurs you'll look terrible.
So your advice is pure catastrophical. Noone should ever go for more than 8cm.

Knee pain is really unpredictable imo and could happen to anyone doing LL due to obvious strain but most of the times it will eventually go away.

What matters here is not how much you decide to lengthen, but how the amount you lengthen changes the shape of your legs and whether doctors are able to prevent that during the surgery.

[KiloKAHN]

This was brought up some years back. This thread also made some interesting points:

http://www.limblengtheningforum.com/index.php?topic=2090.msg33657#msg33657

[heightiseverything]

This was brought up some years back. This thread also made some interesting points:

http://www.limblengtheningforum.com/index.php?topic=2090.msg33657#msg33657

In your opinion, which method allows to minimize malalignment and knock knees? Taylor, LATN, LON, or internals like Precice? Or is it solely dependent on the technique used by the surgeon?

[Body Builder]

In your opinion, which method allows to minimize malalignment and knock knees? Taylor, LATN, LON, or internals like Precice? Or is it solely dependent on the technique used by the surgeon?

Tsf or any other hexapod on tibias (where else) is the only way to have a perfectly aligned bones, of course with an experienced doctor. Nothing else.

[heightiseverything]

Tsf or any other hexapod on tibias (where else) is the only way to have a perfectly aligned bones, of course with an experienced doctor. Nothing else.

What about femurs? I always thought tibias are going to lengthen straightly, as compared with femurs that lengthen into knock knees (valgum). Or maybe tibias tend to lengthen into varum, or vice versa?

[Body Builder]

What about femurs? I always thought tibias are going to lengthen straightly, as compared with femurs that lengthen into knock knees (valgum). Or maybe tibias tend to lengthen into varum, or vice versa?

Always there msy be some malunion. For femurs I don't know if something can be done with internal nails. I think it can't.

[Dragonheart]

What about femurs? I always thought tibias are going to lengthen straightly, as compared with femurs that lengthen into knock knees (valgum). Or maybe tibias tend to lengthen into varum, or vice versa?

From my personal research - tibias lengthening may cause varum or valgum only if internal nail was bent due to excessive load OR tension in your muscles from one side. However, in ideal case if everything goes well tibia lengthening does not affect position of knees as the bone itself is straight and perpendicular to the ground when you stay so if it's kept straight - you're good.
Femur lengthening over internal nail will change the mechanical angle for sure. You may not get valgum only if you already had varum (and if it was caused by femur solely) initially. I've also read about cases in russian clinics where extra correction is performed once your lengthening is done. Correction is done by taking small part of your bone and changing it's angle a bit somewhere in the middle (it get's temporary fixated in this place with a metal plate afterwards) of bone to, let's say, direct femurs a bit more to outer side. Here's what I mean:

 This is a big compromise because - yes, it will help with knock knees as the distance between your knees is restored, however:
1) your bone now get's two axis (right picture, orange lines) instead of one axis in a healthy bone (left image, yellow line). This means that place where two axis are crossed will always get excessive load.
2) Inner part of knee will also get an extra angle meaning that load will not be distributed correctly.

A person that is originally tall does not have this problem because even though they have longer femurs, their femur neck to femur itself angle is different. So the only way to restore original knees alignment for short person doing LL on femurs over internal nail would be to also do manipulation over the place where femur and femoral neck are connected to correct the angle there, however, I have not heard of such procedure in any clinics.

[heightiseverything]

From my personal research - tibias lengthening may cause varum or valgum only if internal nail was bent due to excessive load OR tension in your muscles from one side. However, in ideal case if everything goes well tibia lengthening does not affect position of knees as the bone itself is straight and perpendicular to the ground when you stay so if it's kept straight - you're good.
Femur lengthening over internal nail will change the mechanical angle for sure. You may not get valgum only if you already had varum (and if it was caused by femur solely) initially. I've also read about cases in russian clinics where extra correction is performed once your lengthening is done. Correction is done by taking small part of your bone and changing it's angle a bit somewhere in the middle (it get's temporary fixated in this place with a metal plate afterwards) of bone to, let's say, direct femurs a bit more to outer side. Here's what I mean:

 This is a big compromise because - yes, it will help with knock knees as the distance between your knees is restored, however:
1) your bone now get's two axis (right picture, orange lines) instead of one axis in a healthy bone (left image, yellow line). This means that place where two axis are crossed will always get excessive load.
2) Inner part of knee will also get an extra angle meaning that load will not be distributed correctly.

A person that is originally tall does not have this problem because even though they have longer femurs, their femur neck to femur itself angle is different. So the only way to restore original knees alignment for short person doing LL on femurs over internal nail would be to also do manipulation over the place where femur and femoral neck are connected to correct the angle there, however, I have not heard of such procedure in any clinics.

What about if someone either has bow legs or knock knees? Could this malalignment cancel one or another, if at all, in full?

I am also wondering how does this malalignment reduce your height gain. Obviously, you lose some mm by lengthening along anatomical axis (due to the angle), but you must also lose even more due to the changing angle. Do you know if there is a formula for calculating how much the angle will change after lengthening along the anatomical axis for a certain amount of cm?

[Dragonheart]

What about if someone either has bow legs or knock knees? Could this malalignment cancel one or another, if at all, in full?

Bow legs situation might be improved by this lateral shift that happens after femur lengthening, however, everything depends on what actually causes bow legs in particular case. It might be due to the tibia that is not straight while your femur angles are ideal - in this case you'll just break the biomechanics even more.

I am also wondering how does this malalignment reduce your height gain. Obviously, you lose some mm by lengthening along anatomical axis (due to the angle), but you must also lose even more due to the changing angle. Do you know if there is a formula for calculating how much the angle will change after lengthening along the anatomical axis for a certain amount of cm?

Well, anatomical axis and mechanical axis form a triangle where one angle is 90 degrees. So you can calculate height boost using any Hypotenuse Calculator if you have x-ray and know your angle and current femur length.
https://www.omnicalculator.com/math/hypotenuse
Angle α is 6 degrees ideally. C side (hypotenuse) is your femur length. B side is actual leg length that affects your height directly. We don't care about A so let it be auto calculated.
You can enter values above and then manipulate C side length (take your current length + desired lengthening). There's also a research saying that 10% lengthening adds lateral shift to the angle by 0.57 degrees (angle is decreased), so you can also recalculate angle α for your case so that B side is calculated properly with new C side length.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5434350/