My last post was all about Subtalar joint neutrality. It was a goal of mine to place patients statically there if I could. I am totally aware that this position of subtalar joint neutral is not always attainable with orthotic devices for various reasons. But, as a clinician, and being clear on your objectives for your orthotic devices, attempting subtalar joint neutral position for many foot, ankle, and lower leg problems will provide excellent stability when obtained for your patients.
Back, for a moment, to my students at Samuel Merritt's College of Podiatric Medicine. In my biomechanics workshop, my 3-4 students each month are prescribed orthotic devices. Let look at the data from one of those sessions.
These are my students measuring other students with my supervision. We have 4 students. If we go from top to bottom the numbers go like this.
Student A
Right RCSP 7 degrees everted NCSP 1 degree everted
Left RCSP 9 degrees everted NCSP 3 degrees everted
In student A, the both feet are everted from neutral and everted to the ground. The NCSP defines this student as Rearfoot Valgus (almost normal right and 3 degrees left). Note the consistent asymmetry that is in almost every patient. More on this later. Even though the left heel is more everted, both heels are 6 degrees from subtalar neutral and should get symmetrical prescriptions to achieve this 6 degrees.
What is not on this chart for that day, the day of the initial evaluation, is the OCSP. This is the Orthotic Calcaneal Stance Position. This is a crucial measurement to our understanding of the static changes in our orthotic devices. At dispense, this patient had the heel re-bisected, and the RCSP and OCSP measured. For student A, the OCSP was Right 0 degrees or vertical and the Left 2 everted. How many degrees of varus correction how been prescribed? 7 degrees on each foot. How many degrees of change from RCSP towards NCSP was accomplished? 7 degrees on each foot. The patient, the student prescribing, and I were feeling good about centering this patient. Most clinicians also give a 2 degree variance on either side of neutral as fine. By this I mean, if NCSP is 3 everted, then OCSP from 5 everted to 1 everted is stable.
Any rule like the above has to be individually checked with the patient when they use them. How do they feel if you are several degrees on either side of neutral? Do they feel more stable? This is an important questions to ask any patient you are giving orthotic devices. You need to always make them more stable.
How is 7 degrees attained with your orthotic device? First of all, if you are lucky that they have 5 or more degrees of forefoot varus/supinatus, just supporting 5 degrees with intrinsic support gets you almost there. Medial Kirby heel skives in my hands gives me a degree or slightly more per each 2 mm wedge. Therefore, a 4 mm Kirby skive may give my 2-3 degrees of varus support. Another common method is simply setting the cast inverted to the ground the degrees you want. This is used all the time in everted forefoot degrees of plantarflexed first rays and forefoot valgus. My partner, the now decreased Dr William Olson used this alot in practice especially when he wanted some varus for his athletes. So, you have to come up with the help of your lab, how to take the foot and obtain a 6-7 degrees correction. It is so significant to your patient's stability, that they will brag about you to all your friends. I simply used a 35 degree inverted orthotic technique for this patient to give me my 7 degree change. That 5 degees to 1 degree change ratio almost always works for me.
I was just talked to a doctor that uses inverted cast correction of 3-4 degrees, with 2-3 mm Kirby heel skive, with less than normal arch fill, and is almost always happy with these pronators. I told him to collect some numbers like we are doing here, and see what he was doing biomechanically. It is typically good with the Inverted Technique and Kirby Skives, that you are placing so much support near the heel, that the patient can tolerate higher arch support and overall more correction
Can't wait for Part 4!!
