Lengthening limits and anatomical axis

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From this study

http://www.actaorthopaedica.be/assets/2502/04-Acan.pdf

"Excessive lengthening over 5-6 cm or more than 20% of limb length was reported to be associated with  increased  complication  rates.  (4,11,28).    As  emphasized  by  Paley  et  al,  there  are  several publications recently investigating the theoretical risk of lateral shift of the lower extremity mechanical axis, due to achievement of lengthening along the femur anatomical axis".


I was always of the impression that going over 15% was bad it sounds like Paley put the 5cm rule in for the really short guys 165cm and under and then it got spread in the LL universe but 20% of bone length is apparently fine?

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Quote from: Michael J. Assayag, MD on October 22, 2020, 06:59:33 PMThe most common number quoted is 20% as the upper limit of lengthening.

15% is a conservative, safe measure.

Now when it comes to mechanical axis deviation , I am currently working on a retrospective paper that hypothesizes that the bend in the nail during lengthening negates the lateral shift in mechanical axis.

When it comes to tibia lengthening do you use the 15% measure or go with 5cm max?

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Dr Assayag I posted another thread about something similar to your research, it was a quote from a surgeon name Dr Franz Birkholtz who said the following regarding lengthening over 5-6 cm in femurs leading to malalignment.

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 your opinion that this does not happen and malalignment will not occur for patients lengthening over 5-6 cm in femurs according to your research? Secondly regarding the 15% lengthening limit do you apply that to tibia lengthening or do you have a hard 5cm limit? Thanks

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Interesting. As you mentioned the bend in the 10mm and 11.5mm what happens to patients who would need the 13mm stryde?