Femur Lengthening over 5-6 cm inevitably lead to malalignment

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I was reading this thread about mechanical and anatomic axis and saw that Dr Franz Birkholtz added something that I hadn't read before

http://www.limblengtheningforum.com/index.php?topic=413.0

Quote from: Franz on March 12, 2014, 07:09:54 PMYes 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.
Standing xrays can be taken with Precice nails with certain precautions.

Is malalignment and potential arthritis just one of the prices to pay if you want to do 8cm femur? Is there any way around this?

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I wonder how this would be for people with bow legs. If the axis is changed I wonder if the malalignment would be reversed if it were already malaligned. Also idk if this is necessarily true in general. Doctors like Paley say they won’t risk functionality for extra cm.

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Quote from: Apprehensive Finance on October 24, 2020, 02:32:07 AMI wonder how this would be for people with bow legs. If the axis is changed I wonder if the malalignment would be reversed if it were already malaligned. Also idk if this is necessarily true in general. Doctors like Paley say they won’t risk functionality for extra cm.

No idea for bowlegs. I believe Dr Birkholtz was talking about patients who don't have deformities.

Many Paley patients have done 8cm femurs so I'm not sure if that's a good example as it's quite possible someone could still be functional with a certain degree of malalignment. As you previously mentioned bow legs and there are many people who are mildly bowlegged who are very athletic.

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This doesn't apply to bowed legs/tibias at all.  What he's talking about is that your femurs don't go straight down from your hips, they go towards each other slightly, so the more they're lengthened, the closer your knees will become when you stand and walk (unless you purposely adopat a wider stance).

Bowing of the tibias can be corrected at the time of surgery, but I think there are limitations to what's possible.  A Beijing patient said he would've gone to Paley and gotten internals, but he also wanted to lengthen 5 cm, and Paley told him that would be two surgeries.  So he went to Beijing and got it all done with LON.

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There is a new method to lenghten in the anatomical axis without messing it up. Yeah the  world is changing

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Quote from: Khaleddefine on October 24, 2020, 10:41:31 AMThere is a new method to lenghten in the anatomical axis without messing it up. Yeah the  world is changing

Care to elaborate on this new method? What is it and which doctors have performed this method?

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At least birkhotlz is honest. This is an important topic. Bcuz femur is not straight. Biomechanics will permanently change with any LL especially femur. So less is better

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It seems surgeons are split on whether or not internal femur lengthening will lead to misalignment. If you ask Dr Paley, he will tell you that that's not true. I also asked Dr Parihar about it in a Q&A, linking him to an article discussing that potential issue, and this was his response:


LL Forum: In this article by Drs Paley and Herzenberg (http://www.ncbi.nlm.nih.gov/pubmed/22933497), it said that for internal femoral lengthening "there is a lateral shift of the mechanical axis by approximately 1 mm for every 1 cm of lengthening". Wouldn't this mean that internal femur lengthening has a side effect of causing valgus deformity and potentially osteoarthritis of the knee for putting increased pressure on one side of the knee joint? If so, can the nail be inserted in such a way so as to reduce this lateral shift of the mechanical axis?

Dr Parihar: Lot of potential problems with that article. It's a good hypothesis, but far from being proven yet. There are other articles that have shown the opposite (that there is no real change in the mechanical axis.)
        a. They did not correlate the length achieved with the amount of axis deviation. If there is a cause-effect relationship, one should be able to show a positive correlation.
        b. One patient actually moved in the opposite direction (medial axis deviation).
        c. They state in the article that "Because of the potential for errors in measurement or radiological magnification, the data were analysed by considering a total shift in mechanical axis deviation of ≤ 2 mm to be inconsequential. With this assumption, further analysis of these 26 limbs showed that 15 limbs had an insignificant total lateral change in mechanical axis deviation of ≤ 2 mm”. i.e. >50% of the limbs did not have a significant change in the mechanical axis.
        d. The correct comparison would be the immediate postoperative Axis, and the 6 month postoperative axis - because the surgery itself (osteotomy and insertion of the nail) may change the axis.

In general, lengthening less is going to be safer than lengthening more though.

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Very interesting Kilo. At the moment the consensus is that soft tissue stretching too far is the main problem with excessive lengthening, I have no doubt that 6cm femur would have a better long term outlook than 8cm, ceteris paribus.

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6042223/
i said no