Reverse Planning Method: Maintaining & Correcting Mechanical Axis During LL

The Paley study should be very interesting in that if he states that alignment issues are insignificant then it looks like someone developed a redundant method.

Can someone explain why a person would have rpm on their tibia considering all lengthening takes place along the mechanical axis anyway?

Dear Uprising

You are Right as the mechanical and anatomical axis are the same in normal tibiae.
It is not in femurs thought.

What is most important is to make allignment tests before Planning as you can see many different deformities as well in tibiae that should be considered and studied in both AP and Lateral views to prevent malalignment and knee ROM.

Metaphisis is full of cancellous bone and due to distraction It migth cause deviations during lengthening. Sometimes poller or guide screws are needed in order to keep allignment during the distraction/consolidation periods.

On the other hand, tibia Allignment becomes tricky When doing externals for 2 reasons:

1- distraction is applied parallel to the mechanical axis
2- progressive stifness of the callus might cause bending/losening of the pins

For that reason It is quite common to ser tibia valga or femur varus deformities after LL with Externals.

Excellent point

Quote from: theuprising on June 05, 2015, 06:57:49 AMI would be very annoyed if I were a Paley, Guichet or Betz patient and did femurs. Their method looks likely to cause problems especially those who did over 5cm. This is definitely the future of femur lengthening. Great topic.

One of the reasons I think it's important to raise the profile of this issue within the LL community is that although the reverse planning method was developed by a Fitbone affiliated surgeon (Dr. Baumgart), it is not proprietary to the Fitbone process. Paley, Guichet, and Betz could all integrate this methodology into their surgical approaches. They would just have to work to revise the reaming systems they use, so that they can do both flexible and rigid reaming. No changes would be needed to the actual nails, and any competent LL orthopedist could make the necessary adjustments in technique with the right tools.

Quote from: KiloKAHN on June 05, 2015, 03:00:21 PMWould a 6 or 7 mm shift in mechanical axis be significant enough to cause osteoarthritis though? If it is, osteotomy can be done on each femur to correct it though, so it's not hopeless if you've done internals without the rpm.

Curious about that study Paley is releasing in September that is supposed to address this.

We know from observational studies that every single degree of valgus or varus your knees have increases your risk significantly of lateral (valgus) or medial (varus) compartment osteoarthritis. Whether each individual will develop osteoarthritis though is impossible to predict. Valgus deformity induced by lengthening along the femoral anatomic axis can be corrected by distal femoral opening wedge osteotomy as discussed in the previous thread, but it is a significant surgery requiring large incisions and the insertion of large plates along the distal femur. Most would probably live with a few degrees/mm of valgus rather than go through that.

I'm also curious what Paley has pending for publication. I highly suspect it will be a short term study on his patients showing normal knee/ankle ROM and function 1-5 years after internal Precise LL despite the expected valgus deviation.

From my perspective, a perfect mechanical axis should always be our goal at the end of LL. I don't think anything can change that.

Quote from: theuprising on June 05, 2015, 09:35:12 PMCan someone explain why a person would have rpm on their tibia considering all lengthening takes place along the mechanical axis anyway?

RPM would be relevant for the tibias if you are starting with tibial deformities. For example, a lot of normal people have a bit of varus due to mild bowing of the tibia. If such a person wants to get CLL, RPM to the tibias could give you length while correcting this at the same time.

Quote from: Dr Monegal on June 05, 2015, 11:17:13 PMtibia Allignment becomes tricky When doing externals for 2 reasons:

1- distraction is applied parallel to the mechanical axis
2- progressive stifness of the callus might cause bending/losening of the pins

For that reason It is quite common to ser tibia valga or femur varus deformities after LL with Externals.

We've seen more than one of the femur varus deformities even on this site just like you describe with femoral monorails. That's why I don't think they're a good option. In theory though, external tibia LL should I think be very able to maintain the mechanical axis if done by a good surgeon and with a full circumferential frame. For example, using the Taylor Spatial Frame or Hexapod on tibias with a competent surgeon, a good alignment should absolutely be expected. The only problems with the external tibia approach as KiloKAHN can I think attest are it's painful, debilitating, and slow.

Thanks as always for posting, Dr. Monegal. As we discussed, if you can forward any materials regarding the practical aspects of alignment/immobilization during reaming/nailing with this approach, as well as margin of error, I'd very much appreciate it. Please feel free to e-mail me anything you think might help with understanding this process.

Thanks to thz great info              ..cherry

Hi tall .ur senior .i hv doubts .i want to do internel ....which metjod is safe .and which method u did...cherry

@Maximize:

What do you think of Dr Parihar's response regarding that study by Paley/Herzenberg about mechanical axis shift?

QuoteLL 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.

http://www.limblengtheningforum.com/index.php?topic=2783.msg43784#msg43784

I believe that Dr. Paley has a new article coming out which puts the mechanical axis deviation issue to rest. Would like to check that out for sure. If there's no problem with the deviation then that's definitely another advantage to do femur LL over Tibia, especially if it's only like 3-4cm which is fine for me.

Quote from: KiloKAHN on April 05, 2016, 10:09:34 PM@Maximize:

What do you think of Dr Parihar's response regarding that study by Paley/Herzenberg about mechanical axis shift?

Those are all valid points. My thoughts are as follows.

The anatomic axis of the femur is 5-7 degrees deviated from the mechanical axis. Thus a shift in the mechanical axis is mathematically required and expected by lengthening along the anatomic axis (femur). However, I think I am coming to believe that current methods of internal LL are slightly inaccurate by nature, and so what you get will vary in practice. Furthermore, xrays are slightly inaccurate by nature as well, and if you are trying to measure down to the mm, even subtle variations in how close the patient is standing to the film or their exact foot position may throw it off.

I think it is a combination of those two factors that obscure the shift we expect to see from these surgeries.

Regarding surgical variations, you can view the Precise operative technique here:
http://ellipse-tech.com/wp-content/uploads/2014/06/preciceproductpage/p2femuroperativetechniquelc0083a.pdf

There are many moments where a slight variance in the expected pathway of lengthening could be introduced and those small variances could dwarf the expected small mechanical axis shift. A lot of what I'm about to say is speculation on my part as I've never talked to a leg lengthening surgeon about this or been present to watch one. However the principles are general to orthopedic surgery.

When you ream the canal, the exact point of entry is very important. Additionally, the ream suggested is flexible and will follow the "path of least resistance" through the bone. The exact shape and direction the canal that is created will follow will therefore not be 100% predictable down to the mm. Everyone's femurs will allow a slightly different pathway.

Next when you create the osteotomy, the distal segment now becomes "loose" and unfixed relative to the proximal segment. Even a slight shift or rotation in this segment as the nail is inserted through it could now throw things off in unexpected but small ways.

Then when you screw (fix) the lengthening nail into place, there is a small bit of shift that could be anticipated depending on how snug the lengthening nail is within the reamed canal, how weak the walls of the reamed canal are, and what forces are applied as the fixation screws go into the bone and add lateral compression forces.

Here is an example of a Precise internal lengthening xray:



You can see that the nail runs a little "lateral" at the top through the femur and then ends up more "medial" at the bottom where it is fixed. ie. It is not the perfect expected pathway you would predict if you were drawing the nail over the original preop xray. Other xrays of internal lengthening will often show other similar slight variations depending on the case.

Dr. Parihar is absolutely correct - the only way to truly prove that leg lengthening shifts the axis would be to do xrays immediately after surgical fixation and then again after lengthening. Doing so would take all the small variances I just described out of the equation as once fixed, we expect the nail should no longer shift. However, this is honestly unnecessary in my opinion as we know a small predictable shift is mathematically inevitable.

Dr. Guichet published a list of cases where he showed no statistically significant trend of deviations in the axis. Paley's cases show no obvious major trends either. But a deviation is an expected mathematical outcome. Errors in xray and surgical procedure may obscure this outcome. However, i can see no reason not to plan for it to ensure it is as minimal as possible, and that is what the reverse planning method is about. There is no downside for a surgeon to use it, and it applies to all devices and surgical approaches.

anyone why this method still not applicable ?

Oh wow, I just realized all the diagrams in my original post disappeared. I will have to ask a moderator if they can manually add some new ones. This is the problem with not having photos uploaded directly to the forum - the links can die and things become lost.

Quote from: 184dream on December 12, 2020, 09:13:36 AManyone why this method still not applicable ?

My speculation as to why this is not a major approach is because in the scheme of things it is a somewhat minor issue. It is also sometimes the case that a good technique exists but surgeons don't adopt it because they simply don't know about it or aren't comfortable doing things different than they've always done.

An example, might be PEMF/LIPUS which according to studies likely should be used in all LL cases and yet is not:

http://www.limblengtheningforum.com/index.php?topic=66326.0

The Reverse Planning Method by Baumgart was only published in 2009 making it a very new concept that would not have been around when most current surgeons trained. Not all surgeons are open to new ideas once they become set in their ways.

Perhaps they ought to be using this approach in theory but they feel the margin of error is so low to get it exactly right and it's just "one extra headache" so they don't bother. One can only guess. We'd have to ask some surgeons directly to know.

Another possibility is that to angulate the bone fragments for a perfect RPM approach, you might need to ream the femurs a bit more so you have that leeway, and this could weaken the femur if done too much.