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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The 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.

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Quote from: Michael J. Assayag, MD on October 22, 2020, 06:59:33 PM

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.

Is this for internal femur (stryde)?

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yes. most 10mm nails and 11.5mm nails will bend up to 3 degrees . The nuvasive engineers take it into account when doing testinga so it is a known and expected phenomenon

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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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Quote from: Michael J. Assayag, MD on October 22, 2020, 10:23:35 PMyes. most 10mm nails and 11.5mm nails will bend up to 3 degrees . The nuvasive engineers take it into account when doing testinga so it is a known and expected phenomenon

Gotcha. Say a patient comes in with slight bow legs already, can those be corrected or will they be made worse if he does 5 cm internal femurs, with the Stryde nail? Is there any technique a surgeon can use to correct that or prevent it from getting worse?

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Yes, The reverse planning method and retrograde lengthening should be done. Theoretically at least

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Quote from: Michael J. Assayag, MD on October 27, 2020, 02:27:53 PMYes, The reverse planning method and retrograde lengthening should be done. Theoretically at least

I thought retrograde lengthening is generally not used due to potential chronic knee pain, and most surgeons do anterograde nailing (thru the hip)

Is there no way to achieve results through anterograde insertion?

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It depends on one’s lengthening philosophy.

I rarely perform cosmetic retrograde lengthening unless correcting a deformity concomitantly. There is no way to correct a deformity and do an antegrade lengthening , unless the deformity is at the top.

Baumgart from Munich only lengthens in a retrograde manner using his reverse planning method.

I am currently analyzing radiologic results of close to 300 femoral nails lengthened along the mechanical axis. My hypothesis is that the lateralization of the mechanical axis is offset by the bend in the nail at full distraction for most commonly used nails

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Quote from: Michael J. Assayag, MD on October 28, 2020, 07:50:31 PMIt depends on one’s lengthening philosophy.

I rarely perform cosmetic retrograde lengthening unless correcting a deformity concomitantly. There is no way to correct a deformity and do an antegrade lengthening , unless the deformity is at the top.

Baumgart from Munich only lengthens in a retrograde manner using his reverse planning method.

I am currently analyzing radiologic results of close to 300 femoral nails lengthened along the mechanical axis. My hypothesis is that the lateralization of the mechanical axis is offset by the bend in the nail at full distraction for most commonly used nails

Hi dr. Assayag, could you say how much common is the nail bending? Is it seen during the distraction phase only while full weight bearing or more later too ?
Thanks