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,
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 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.