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Hi thought I would start a discussion about something I´ve been thinking about for awhile now and one of the many reasons why I want :santa: to bring me a CAD/CAM system with mill.

I use heel lifts for a lot of treatment plans for many different conditions. I use a standard product 10 or 7 or 5 mm. Grinding heel lifts by hand gives me nightmares.

Is anyone making their on custom heel lifts ? with or without a mill

I can see many benefits, with being able to have different lenghts, height, pitch, density of material etc.

If you are doing your own customs how are you making you clinical assessments on what is required and do you think it has changed your treatment outcomes, or do you think it´s a big waste of time and the off the shelf works great.

 

Cadcam is great when you want a permanent raise built in to an orthotic but otherwise I grind them by hand.

I think the biggest difference from the off the shelf ones is that I tend to make them longer, often just proximal to mets. with a very gradual bevel. seems to work better through midstance, and also for running.

Dual density is often useful- just had a chap in who fractured his calc and has several screws in. Needs a raise 10mm raise but can't tolerate anything too hard in contact with the heel.

 

Hi Ian,

I´ve found a heel lift that is quite long as I like the longer lift as well. But what do you think of how exact your lift is i regards to gradent ?

ie a milled device would be very specific, but hand grinded a little off here and little there if you see what I mean. and then is it important ?

I used 10 mm ppt for those wanting soft lifts but once again see the benefits of final design and product with a milled product, maybe I building the benefits of system up too much and will be disappointed with Santas present ?

 

I was thinking along similar lines at one stage. But:
Orthotics design software is generally not geared to doing discrete components. You could of course use generic CADCAM software but that takes more time to learn.

In terms of milling- I think you want to work mostly in polyprop, which would be reconfiguring the machine every time you wanted to do a batch of raises- possible but another irritation.

There is often a degree of hand finishing still involved. Not much when it comes to a complete orthotic, but when compared to just doing a heel raise by hand in the first place I don't think it's worth it.

In terms of accuracy by hand, I think the term 'within tolerance' covers it ;)

 

http://clearlyadjustable.com/

 

Hi Graham , do you use the product ?

if so whats the density like ?

Anyone else use them ? Can you get them in Europe ?

Looks intersting would not mind a look see.

 

Hi Michael

Try http://www.algeos.com/acatalog/Clearly_Adjustable_Lift.html

 

Solid plastic in 1mm sheets. Great for determining functional Vs Actual discrepancies. Once you have established the right height it is better to then use a solid lift as these don't hold together well unless you glue them.

 

Thanks Ian Not at that price, back to the grinding wheel when required and dream about the mill, probably to find as you said a pain and back to the grinder.

 

My thoughts entirely. I'd rather spend the money on a :drinks

 

One recent change to OreTek maintains the rearfoot/forefoot plane relationship regardless of the amount of heel lift. This was done to allow for more control over the grindoff or motion on the medial distal edge of the heel. Just simply adding material to the base of an extrinsic post would normally kick the proximal edge of the heel into the air, requiring grinding to maintain the rearfoot/forefoot plane. Now, 3 points in space, 2 on the distal edge of the device, and one at the heel center form a plane to determine the amount of material to add at any given point on the heel, without disturbing the motion grindoff.

 

I choose not to use pre-constructed heel lifts among our offices. In making my own, I can pattern them to individual patient needs. In addition to aforementioned length, I also have a far greater variety of materials from which I can choose based on patient weight, activity type/level, and compression resistance. Commonly used materials include high density polyurethane, cork-EVA and cork-rubber copolymers, and Vibram rubber crepes.

 

:good:This thread just got interesting to me.

OK, so lets talk about bipedal spring-mass walking. The leg stiffness (kleg) in the sagittal plane for each leg is given by:

Kleg = F / x
Where:
F is the force applied on the body
x is the displacement produced by the force along the same degree of freedom

When we add a surface (heel lift) beneath the leg we effectively add another spring in series so:

The effective stiffness of the leg plus surface = Keff, this is given by:

Keff = (1 / k1 + 1 / k2) -1

where
k1 = leg stiffness
k2 = surface stiffness

Heel lifts, by there very intent are unilateral devices. So by adding a heel lift we have added a spring in series to the shorter leg and influenced the effective stiffness of the leg +heel lift system on one side of the body- right?

SO, questions:
1. in a leg length discrepancy is there a difference between the leg stiffness in the long and short legs? (my view- yes)

2. Should the addition of a heel lift aim to equalise the leg stiffness between the longer and shorter legs? (my view- yes)

3. Does simply adding a lift, regardless of it's stiffness, create equality in the stiffness of the long and short legs (my view- don't know, possibly not. So, the stiffness of the material that the lift is made of may be significant).

4. if we have left and right legs (springs) of the same stiffness, but the left has a longer resting length than the right, how does this influence the amplitudes of oscillation of the left and right legs? Answer to this one (at least) here: http://www.myphysicslab.com/spring1.html drop the damping to zero, leave everything else the same except spring rest length, observe what happens to amplitude of oscillation...

Thanks Jeremy.

 

Completely agree, Simon. That also helps explain why the necessary application of between-sole shoe lifts is best made with care to selection of both materials and rockering profile, in the hope of creating bilateral symmetry.

 

Great Points Simon, but how are you making these clinical decisions on what material you use in your heel lift? ie how do you work with you K1 and K2 clinically.

And as we have discussed before we maybe able to influence leg stiffness through changes in mechanics as well.

When would you decide to use a change in material to attempt to influence leg stiffness and when would you go for mechancial ?

 

Mike, I don't have all the answers. I would go both all the time, maybe look at hopping leg stiffness on long leg, look at hopping leg stiffness on short leg then add in a lift of correct height and stiffness to make leg length and keff on short limb the same as length and kleg on the long limb.

 

Craig has talked before about using bilateral heel raises of differing densities to promote a more symmetrical gait:

http://www.clinicalbootcamp.net/heel-raise.htm
http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=3057

Thoughts on kleg being a potential mechanism here?

 

I was thinking along the line of low arch - high arch. From the paper which linked different arch hieghts to leg stiffness (kleg)

ie low arch reduced leg stiffness - softer heel lift in the hope of a CNS response to increase leg stiffness and deal with the LLD

high arch increased leg stiffness- harder heel lift in the hope of a CNS response to reduce leg stiffness and deal with the LLD