Total Pageviews

Followers

Dr Blake's Book

Translate

Sunday, September 5, 2010

Inverted Orthotic Technique: Determining the Arch Height

Rich,



I believe I recall reading in your chapter in Ron's book that chose the arch height in the finished device. I was wondering how you chose the arch height.



For those who don't know how an inverted cast is made: A platform is built on the positive cast that inverts the heel bisection. If you take a cast and invert it, this will make the medial arch of the device higher. Plaster filler is added to the arch and then shaped like how the arch would have been had the cast not been inverted.



Thanks in advance,
T8WGDCPUEEMP


Eric

     This is a question from the podiatry arena website from biomechanics expert Dr Eric Fuller. I hope for some of my followers this information on the Inverted Orthotic Technique I invented in the early 1980s proves to be somewhat interesting. The Inverted Orthotic Technique is my biggest contribution to the podiatry world and has helped tens of thousands of patients.

     One of the biggest problems I see in having this technique more widespread is highlighted by Dr Fuller's question. How is the arch height of the Inverted Orthotic Device determined? Once an orthotic laboratory understands the answer to this question, the technique gets simpler to manufacture for other health care providers. Any laboratory can learn the technique and gradually CADCAM systems will make the process alot easier.

    The Inverted Orthotic Technique is different from a balanced Root or Root Modified orthotic device since a varus cant is placed into the device by inverting the plaster mold a set amount of degrees. The standard is 25 degrees Inverted since it controls pronatory forces better than a Root device inverted 3 degrees with maximal arch height and with a Kirby skive. This was the standard for many labs in the 1990s if they were uneasy to use the Inverted Technique. When a patient was still pronating through the orthotic device, the next correction would be a 25 Degree Blake Inverted. This was the next step in correction and therefore a good starting point for utilizing this technique. If the prescribing clinicians were happy with the control of a Root Device with MCC (medial column correction) and 4 to 6 mm Kirby, or extended Kirby, then there was no need to change to the Inverted Correction.

     The Inverted Orthotic Technique in the world of controlling pronation forces therefore starts at a 25 Degrees Inverted Cant and goes up from there. The higher the Inverted cant becomes, the higher the arch height becomes. I have many posterior tibial dysfunction patients that are functioning well with even 45 Degree Inverted Canting, MCC, 6 mm Kirby and 3/16" polypropylene, and 0 degree extrinsic posts and 25+mm heel cups. You could never attempt such a correction if you didn't solidly know the answer to Dr Fuller's question. It takes a biomechanical expert to ask the question that is at the core of the technique, and I thank you Eric for that.

     Steps at designing the right arch height for the Inverted Orthotic Technique.

The photo above shows 3 positive casts all poured to vertical and then marked at two standard points: low point on the heel and bisection or low point on the first metatarsal head. These are two easily found landmarks.



A ruler is then used to first find the bisection between these two points, and then a second point 1 inch closer to the heel.



Here the wider line is at the bisection mark and a second mark is 1 inch more proximal (closer to the heel). As you will see by the photos that follow, it does not really matter that one inch is used on size 18 feet or size 7 as the extremes of the 3 feet I demonstrate. Now these lines are carried all the way medially and to the top of the positive cast.



See these same marks applied to three different size feet. The biggest one is my son Chris.


Now the casts are canted the desired degrees with the whole foot inverted. I will use the standard 25 degree inverted cant on all 3 casts.



The two photos above show the nails used to invert these 3 casts 25 degrees each.


Plaster is laid down to make an anterior platform.


You can begin to see the Inverted cant being applied to the heel, arch, and forefoot.



After the Inverted Cant is applied, plaster is worked into the arch to begin to create a supportive but comfortable product.


It is very important to not lose track of those crucial arch lines while placing on the plaster.





In designing the right arch height on the Inverted (or Blake) Orthotic Technique, you must remember the Golden Rule of Foot: The highest point in the medial arch is proximal to the first metatarsal (within the marked area). The area in front of these lines toward the big toe must drop smoothly (without high spots) to the platform. In this way, the first ray is allowed to plantarflex and there is no supination moment on the long axis of the midtarsal joint.


You can see that the crucial area within the marked lines is relatively flat with an slight upward slope towards the big toe.



See how the highest part of the arch is within the marked area. The plaster is very smooth in both directions from that point. There are no high spots under the first metatarsal to block plantarflexion of the first ray. There is tremendous medial heel and talo-navicular area for medial support to combat pronatory forces.



Imagine the supinatory moment applied with this standard 25 degreee Inverted correction to the subtalar joint axis.


With the Inverted Orthotic Technique, it is important to maintain the fifth metatarsal  and most of the heel devoid of plaster buildup. The lateral heel expansion should be 2 or 3 mm and follow the natural curves of the heel.



The lateral edge of the buildup should be straight with the heel and the fifth metatarsal should be the highest point of the buildup (lowest point when you turn the mold over).



Here you can see with 3 different size feet that the marked area was the high point on the medial arch and the plaster fell smoothly away towards the big toe.



I will finish this introduction with the photo. I know I have alot of teaching to do and I am so glad this blog can help me in this regards. The focus of this post was based around Dr Eric Fuller's question on medial arch height. I hope that the photos and text have helped you get a clearer picture of the technique. If you look at this photo many key points are worth noting. These are:

  • The area marked is the highest part of the arch.

  • The lowest points of the orthotic device will be the heel, the fifth metatarsal shaft, and the entire anterior platform which sets the Inverted Cant.

  • The plaster must be a smooth transition from this marked area upwards towards the big toe, upwards toward the anterior platform, upwards towards the fifth metatarsal shaft and cuboid, and then smoothly blend with the heel.

  • The heel area must be devoid of plaster as much as possible, with the lateral and posterior expansions 2 to 3 mm and following the curve of the heel.
Thank you so very much, now back to my lab.

2 comments:

  1. How well is this modification tolerated by severe pronators? How often do you use this technique? Do many labs perform this modification, and, if so, do they do it correctly?

    ReplyDelete
    Replies
    1. Thanks for your comment, and I am so sorry it got lost in my pile. I use the Inverted technique on over 1/3 of all my patients each month. The tolerance is well accepted, but it takes a while to understand the pressures and how to adjust. I have worked with my labs who use the technique, but can not do any quality control. These include Root Lab, Richey Lab, Pro Lab, Allied OSI to name some. Overall they do it fine, but some go with a flatter arch, some narrower design, etc. Hope this helps. Rich

      Delete

Thank you very much for leaving a comment. Due to my time restraints, some comments may not be answered.I will answer questions that I feel will help the community as a whole.. I can only answer medical questions in a general form. No specific answers can be given. Please consult a podiatrist, therapist, orthopedist, or sports medicine physician in your area for specific questions.