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Sunday, June 24, 2018

Clinical Biomechanics for Podiatry (Post # 1): Orthotic Designs: Positive Casts before Balancing

In designing orthotic devices, to achieve positive functional changes, and positive symptom outcomes, the prescribing health care provider needs to be fluent in orthotic casting, orthotic prescription variables, etc. I took 20 casts of my wife Pat's left foot to show common variables in orthotic prescription writing. The first cast I poured with plaster and left it uncorrected (the yellow positive cast below). The other 19 casts of her left foot I corrected various ways to achieve various functional results. I will try to show you that even though a good cast is taken (podiatry's Gold Standard in Root Biomechanics), your goals of what you are trying to achieve functionally and symptomatically may require a wide range of orthotic variables.

These 3 positive casts were made for 3 different patients: Orange for high degree of Forefoot Varus, Pink for high degree of Forefoot Valgus, and Yellow (my wife Pat) for a Neutral to Slight Varus forefoot to rearfoot relationship. 
Here are these 3 feet seen from the back of the heel. These represent the negative cast which were taken of three left feet. The Orange cast of a high Forefoot Varus deformity shows the heel collapsing into valgus to get the front of the foot to the ground. The Pink cast of a high Forefoot Valgus foot type shows the heel falls into varus to bring the forefoot to the ground. The Yellow cast (my wife) represents the more Neutral Forefoot to Rearfoot showing the heel position more near a vertical position. The orange and pink foot types are simple to analyze and correct and untreated can lead to devastating foot compensations and pain syndromes. 

Here is a blow up photo of two left feet positive casts. The one on the left shows FF Varus where the forefoot is inverted on the rearfoot. 20 to 50% of patients have this problem. After the foot lands on the ground, to get the big toe to the ground, the arch must collapse and the heel roll into valgus causing severe over pronation. The cast on the right (pink) shows a left foot of FF Valgus. This foot type must roll the heel out to get the metatarsal weight evenly spread and the foot stable. However, this outward roll of the heel, also called over supination, under pronation, or lateral instability, causes a very unstable foot. Try standing on the outside edge of your foot and see how stable you feel. The goal of orthotic devices with these 2 foot types is to get the feet balanced, centered, with the heel straight up and down. This is the goal for what is called Root Balance Technique. 

The Yellow cast of my wife's left foot shows a very Neutral foot. It is very stable. All the negative casts are poured with the heel vertical by propping up one side or the other to get the vertical heel position marked on the cast to be perpendicular to the top of the foot. This is the Gold Standard of Root Balanced Orthotic Devices, but can be your reference in other cast corrections such as the Inverted Orthotic Technique. 

This is a soft based orthotic device made directly off the uncorrected positive cast. By uncorrected, I mean no attempt was made to change the position of the foot. I will demonstrate in some of the upcoming posts, how simple changes to the positive cast correction can make powerful changes in the foot position. This soft based orthotic device is called an Accommodative Device and more correctly called a Hannaford Device (as first invented by Dr. David Hannaford).

1 comment:

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.