People talk about 6cm being the safe limit for femurs. I'm already way past that and I've met lots of other betz patients who have passed that and have or are having a good recovery. So where does this safe limit originate? Do the surgeons who advise this do it because their nails or techniques do not allow them to go much beyond that? Is it their insurance companies telling them to say this to cover their asses against future liability claims? Are there documented cases of really bad things happening? Fwiw I got minor nerve damage beneath my knee at 5cm, since then everything has been fine. I'm at 8cm and could easily go more (my body isn't freaking out). I hear people on this forum refer to it as though it's some kind of gospel thus perpetuating this (what could be) a theoretical or "finger in the air" safe limit. Just wanted to hear what people think.
The 'safe' limit, who came up with it?
Hi. There are some papers about this safe limit and i think it's more about 7.5 cm for the tibia. But as it is an average limit it only means that most people shoudln't do more. And it should mean that the "safe" limit is also a little more if you do femurs. As i said its only around 7 cm for most people, but you can do 9 cm and be ok, or more. It depends on the technique used i think also (external or not). Well this is my POV.
Good question, I believe a lot of doctors suggest this limit, but there's no real studies or evidence to show that it's unsafe to go beyond the amount. Doctors generally recommend at most 5 cm on tibias, but then you have other doctors who are willing to do 12 cm on the tibias without any concern. Guichet has a 10 cm limit because that's as long as his nail will go and Paley has an 8 cm limit for the same reason.
I think everyone's bodies are physiologically different and some people can go above and beyond what others do. It's all about how your body responds to the lengthening.
I highly recommend reading the Dr Birkholtz thread and Dr Lee on old forum where they discuss this.
Other than obvious proportion issues it has alot to do with your soft tissues, they can only be stretched
to a certain point before they become permanently weakened. Dr Lee suggests you should ideally lengthen 15% of original bone length however up to 20% is possible. I don't think they are just
saying it to cover their asses rather what offers the safest and most reliable recovery for the patient.
Dr Birkholtz also mentions that the greater the distance lengthened the higher the likelihood for arthritis
later on. As I mentioned earlier he explains it far better than I can in his thread so check it out.
I guess the safe limit is an individual matter. Some people can go for further lengths while others may not. Some doctors say not to go beyond 5 cm in any segment, some say you can do moderate lengthening upto 7.5 cm while other doctors do permit beyond 8 cm. Dr.Lee suggests 15% of the original bone length so people with longer bone will be able to lengthen more.
But then again, most doctors usually encourage people to stick with small targets as possible, maybe due to higher risk of early arthritis from the added pressure on the adjacent joint (more length=more pressure). Another possible reason is that internal femur lengthening is along the anatomical axis which causes a change in the mechanical axis. Here is the quote from Dr.Birkholtz
Quote from: Franz on March 12, 2014, 06:59:16 PMGreat question,
Yes with exfixes we lengthen along the mechanical axis which should correspond pretty much to patient height. With femoral nails, we tend to lengthen along the anatomic axis, which might not correspond perfectly to height gain (it is oblique). It is well described too that patients end up with 5-10 mm less than expected. I would suggest going 1cm beyond target length and then backing the nail up by 5mm. This would ensure quick consolidation. The downside of long lengthenings along the anatomic axis (like with precice, guichet, betzbone, iskd), is that we change the mechanical alignment of the femur, as we lengthen along a different axis. This means that intramedullary lengthenings in the femur beyond 5-6cm will inevitably lead to slight malalignment. This may in time lead to arthritis.
In short, keep to reasonable distances and go to a doc that understands this.
So from this perspective, the "safe" limit not only tries to reduce risk from the complications that may arise during lengthening but also tries to reduce the risk of developing arthritis in the long term.
Quote from: BilateralDamage on May 11, 2014, 03:53:52 AMGood question, I believe a lot of doctors suggest this limit, but there's no real studies or evidence to show that it's unsafe to go beyond the amount.
There are some studies. Anyway you just have to listen to your body (feel the vibe 
).
Gettingtaller want to know why you are asking now and not before you started lengthening?
This question will be answered 100% honestly, when other doctor's devices will be able to lengthen more than they can now... ;-) Paley used to say that 6,5cm is safe... That's what precice 1 was able to lengthen.
In general, it depends a lot on your individual body and healing capacities
Quote from: theuprising on May 11, 2014, 09:56:36 PMGettingtaller want to know why you are asking now and not before you started lengthening?
Uprising, why do you assume I didn't??
Quote from: gettingtaller on May 12, 2014, 07:14:15 AMUprising, why do you assume I didn't??
Obviously since you are already way past the recommended limit. Second obvious one
is that you made this thread.
My thinking was exactly like yours when I first found LL wanting to do the maximum amount
and finding a surgeon who would do it. The more I researched you realise that just because
something can be done doesn't mean it should. This being said good luck with recovery if
you had a tall enough starting height you should have a better time of it.
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