Bisecting the Negative Cast for Orthotic Manufacturing

I apologize for most of my readers that this means little, but this bisection line on the back of a negative cast to me is crucial in designing orthotic devices. To complicate matters worse, the bisection line must be "tangent to the curve on the lateral side of the heel", whatever that means. I know what it means of course. But, when you are learning this stuff, it can be difficult, and sometimes impossible to learn. The lateral side of the heel is the opposite side from the level, and looks fairly straight. When you use Root Biomechanics, 1 degree changes are important, so a heel bisection 2 or 3 degrees off, can be disasterous. With the Inverted Orthotic Technique, with a rough estimate of 5 degrees of cast inversion to 1 degree foot correction, the exact bisection is not as crucial. 

Video on Orthotic Modifications for Pronation Control

Thursday's Orthotic Discussion of the Week: Root Balanced Technique evaluated in a left Positive Cast

Dr Merton Root in the late 1960's developed many methods to stabilize feet. He developed a way to cast feet to achieve a reliable, reproducible foot. This cast, called a negative cast, was taken using plaster of paris splints and the foot was held in a certain way, and this became the Golden Standard of making orthotic devices. Once the cast was taken, the heel was placed straight 

Podiatry Talk: Over Pronation in the Left Foot

Dr Blake's Intro: This very dedicated podiatrist was so kind to call me about 3 patients she was going to prescribe orthotic devices for just prior to my July 4th Holiday. You can sense the passion and kindness that all of us would like to find in the doctors/therapists that help us. Don't worry if the numbers or abbrev are confusing. I will try to explain the gist of it.

Here is the back of a right foot (could not find a left in my immediate files) very pronated (EV) or everted. The ruler represents vertical or straight up and down (where you want your foot to be in general)

Here is Julio's same right foot very pronated with the goniometer we can use to measure the exact angle from vertical. Comparing the right to left can give you a great understanding of the degree of arch flattening of one foot over another.

Dear Rich,


I wanted to Thank-you for trying to reach me on Th am before your ( much deserved vacation for the 4th of July ). I know what is like on the last day at work before an upcoming holiday/ vacation/ absence planned. It seems as though "everyone and their mother" + grandmother + father+ child+ ...uncle... needs you... Pun intended : )

So many people in pain or in precarious weight bearing situations- (like the pts I described to you ) rely on your expertise and it all takes time. It was very thoughtful of you to squeeze me in as well.

Dr Blake's Note: my voicemail must have been cut off, however this form of communication should prove more useful.I listened to your VM to me & I am not sure what happened, but you broke off in mid sentence and the recording abruptly ended. I thought I might be able to reiterate what you would do with the patients I presented and you could let me know if I have down your complete answer.  Below I have included a recap since it has been awhile.

Dr Blake's Note: The podiatrist describes the complicated biomechanics of three patients all in their 70s and all with collapsed (everted or pronated) left feet. I think there are 2 common forces that produce unequal wear and tear on our musculo-skeletal system as we age: The presence of limb dominance produced by being right handed or left handed where right handed people have the left side as their support leg and break it down quicker, and the limb dominance of having a short leg. 80% of people have a short leg and it seems to me the majority have the long leg on the left. The longer leg has more compression forces as the body levels itself out at the spine throwing more weight to the left. The limb dominance seen in a long left leg in an adult is typically greater weight bearing on the left.



PT Backgrounds/Recap: The patients are 75+ yrs. in age with c/o recent balance problems. Each patient has their mid arch L ft collapsing with palpable bone plantarly. All have slightly boney dorsal prominences at 1st met heads.

Dr Blake's Note: There are 2 major reasons for balance problems (ie the patient feels unsteady on their feet. With one foot beginning to have arch collapse only on one side, the delicate symmetrical balance between the feet are thrown off and instability ensues. And pure arch collapse on one or both sides leads to great feelings of unsteadiness. From a patient's standpoint, they have a difficult time knowing where the instability is coming from. The medical world also wants to blame things like this on their age, failing to recognize it can be a simple (ha ha!!) foot problem, with a sometimes simple solution. Evaluation of foot structure, especially looking for anything assymmetical like uneven pronation, should be part of any balance program/fall prevention program.

PATIENT #1: RS
R.S.= Pt Male:175lbs, 5'10 The gentleman has more severe balance issues in that he shuffles,uses a walker and does not walk much. He has severe gout with tender tophi on his great toes IPJs. B/L: Tibial valgum and Extensor Substitution

Left: Tight plantar fascial band upon palpation with Pl Fasciitis pains in arch and more distal than heel region; slight hip drop, hits EV on heel strike
STJ: 14 Inv, 10 Ev ; RCSP: 2 Ev NCSP: 90 Foreft (FF) is 3 Pronated/Ev on Rearft (RF)

Right: STJ: 12 Inv, 4 Ev ; RCSP:1- 2Inv NCSP: 4Inv FF to RF is 90 ; slight Rt shoulder drop

Dr Blake's Note: Simply put the left arch is collapsed with the heel everting (see photo above). The left hip drop show limb dominance to the left, therefore more compression forces, further collapsing the left foot. The slight right shoulder drop is typically seen in a right handed individual.

PATIENT #2: CH
C.H.= Pt Female:156 lbs, 5'6 States that she feels a "pulling" & feels like she is "walking on rocks" in and out of shoes. Likes to walk for exercise.

slightlyskewed-shaped,very pronated Left: STJ: 16 Inv; 9 Ev ; RCSP: 5 Ev NCSP: 2 Inv FF is 11 Supinated/Inv on RF slight L shoulder & hip drop

Dr Blake's Note: She is more everted than the first patient. She has the same left sided hip drop increasing the compression forces on the left. Uniquely, she has a very tilted or supinated Forefoot to Rearfoot relationship. This is opposite of the heel angle. The more supinated or inverted the forefoot is, the more eversion or pronation force is placed on the heel. The higher this number goes, the worse the problem.
RT: STJ: 30 Inv; 4 Ev ; RCSP: 2-3 Inv NCSP: 2 Inv FF is 19 Supinated/Inv on RF
Dr Blake's Note: I find this foot very unstable. The right foot has such higher forefoot supinatus or inversion, yet can not evert the heel. See the heel still a few degrees inverted. When the numbers don't match up, the body can not do something important to life and it begins to break down. This patient has two bad feet and not a good leg to stand on. Here symptoms match this degree of instability.

PATIENT #3 JP
J.P. = 82yo. rode a bike until 75yrs. leans to L in gait female: 170 lbs, 5' genu valgum
Dr Blake's Note: Here is the third patient with the lean to the left side. Is it the chicken or the egg?
slightly skewed-shaped,very pronated Left: STJ: 23 Inv; 15 Ev ; RCSP: 5 Ev NCSP: 2 Inv FF is 4 Supinated/Inv on RF slight L shoulder & hip drop


RT: STJ: 22 Inv; 4 Ev ; RCSP: 90 NCSP: 2 Inv FF is 1 pronated/Ev on RF


Dr Blake's Note: When I was left the telephone message, there were no specifics. Now that we have the specifics, the RX can be more finetuned.
So Rich your recommendation was to use a polyprop shell, covered with pink plastizote, with leather glued as the topmost cover. The poly shell should be at: A) 5/32" if I have a grinder such that I could grind down the arch if needing more flexibility/softer tics or B) 1/8" and the following materials could be added: korex (1)Thickness?)  (Dr Blake: 1/4 inch) or grinding rubber? could be added under the arch-how far along the device? (Dr Blake: from just in front of the post to the highest part of the arch) to the  to add more stability as needed, but the point was to hold that arch up as much as can be tolerated.

Dr Blake's Note: The 3 biggest problems I see with these patients that can lead to poor correction of the foot mechanics are:

1. The pronation or arch support correction is placed equal with no real difference in correcting the more everted foot. Big Mistake!! The flatter foot should end up with the higher arch support (Newton's Law: The side that has more force to flatten the arch, should have a higher support to unflatten it).
2. When you are over 70 years old, no matter how much support you need, it is assummed you must only be able to tolerate less supportive soft supports. Big Mistake #2.
3. You are not treated like a 20 year old, where perfection is sought in all treatment areas. Good enough is too often accepted, when better may be alot better. What do you expect for your age? And when medicare does not pay for orthotics, low expictations abound. Not if this is my mom or dad or me???

You discussed a discounted intro pair and what would the intro pair be made from? Do you recommend using cork or crepe as a shell?
Dr Blake's Note: When I am prescribing orthotic devices and I am unclear of the right inital correction to give, I typically tell the patient that the first pair is my trial pair (which I may hit the mark on the first try, or may have to learn from). Since I figure both I and the patient are teammates in this endeavor, we should share equally in the costs for any orthotic that is truly transitional (although without we would have not been able to get to the final result). I would leave the cost discount to the patient in each doctor/therapist's hands. I did not mean to imply that the trial pair was of any material different than what you feel is best for the patient. I use three common materials in this quest: plastazote for some support and max cushion, 1/8 inch poly for some support and cushion, and 5/32 inch poly for significant support (for heavier patients the 5/32 inch is changed to 3/16 inch poly).


You also pointed out that you would RF post and with a hi RF valgus you might pour inverted (the Blake) & / or Kirby skive. At what point do you decide to do either or both? Then you were cut off.

Dr Blake's Note: So much of this is up to the skill level of the lab. I have toyed around with this for years and have concluded many things. These include:

1. When the Resting Heel Position is over 2 degrees valgus/everted, you can not just rely on arch support, the medial side of the heel must take some of the force to control pronation. This, of course, can be accomplished by either some form of inverted pour, or a Kirby skive. There are many sublties that can effect the correction like FF supinatus/varus vs FF pronatus/valgus, whether the heel is rounded or flat on the bottom, and whether their is a low arch or high arch.
2. When the presenting complaint is in the arch, the patient normally likes more heel correction (Inverted vs Kirby) and less arch correction.
3. Less arch correction can be accomplished with sweet spots,  plantar fascial grooves, or softer materials, but it is a mistake to low the entire arch.

I usually like to make an actual dell in the orthotic device to semi off weight this most depressed point of the arch in order to support it & alleviate pressure. This would match the weight -bearing position. Around the "dell for the boney prominence" I just created, I leave ~1cm raised unskived doughnut section.(unskived immediately adjacent to the "dell for the boney prominence" Then I gradually skive around a ~1cm doughnut which is full thickness to blend with the arch. Dr Blake's Note: Here is a nice example of a Sweet Spot being created.

I am very interested in whatever you have to say and appreciate your thoughts and time.  I  thank you for your pearls of wisdom. I hope you had a great vacation. I look forward to hearing from you. Take Care.

Sincerely, Karen

Karen, Thank you and I know I am late with this response. I hope taking this time on my blog will prove more meaningful than my cursory voicemail comments. So of all of the orthotic devices we have available what should be done.

With as long winded as this post, I best get right to the point. I hope you can follow based on the earlier discussion points. I will try to always prescribe differently for the right and left feet, so we have 6 feet presented to prescribe the initial orthotic to, and learn from. With this learning process, we may have hit gold early, or at least seen how the patient responds to the certain correction. All these orthotic devices should be with 5/32 inch poly to start, 0 degree birkocork rearfoot posts, with 23 mm Heel Cups Left and 21 mm Heel Cups Right and unless I mention a change or possible modification below.

RS #1 Left Pour 2 degrees Inverted or 2 mm Kirby Skive (Skive best effect with a rounded plantar heel and pour inverted best with flatter heel), maximum arch support with minimal fill yet sweet spot accommodation created.

            Right Pour Vertical.

CH #2 Left With the High FF Supinatus on both feet with CH I use the resting heel position to calculate the Inverted Pour. Here 25 degree Inverted pour will correct for 5 degree Ev RCSP. Maximum Arch Support with minimal fill and sweet spot accommodation.

            Right 15 degree Inverted Technique with Maximum Arch Support.

JP #3 Left 4 mm Kirby Skive with maximal arch support or 5 degrees inverted pour. It is good when you have the negative cast to look at the heel and arch from the medial side and imagine how the arch would change when you add a Kirby vs just Inverted Pour. Remember the Higher the Arch initially, the more effect an Inverted Pour with Maximal Support would have over a lower arch. This is also true with a flatter heel. Kirby Skives are better with rounder heels in general.

          Right Pour Vertical.

Karen, I must go for now. Took 3 nights to answer your great email. Hope it makes some sense. Rich

Top 100 Biomechanical Guidelines #43: Sagittal Plane Blockade may Occur with Everted not Inverted Heel Corrections (Forefoot Varus Correction could cause Blockade of Motion)

These are Forefoot Varus Casts. Uncorrected then lean inward and the arch would flatten and foot pronate. Correction of this foot has always been a dilemma for biomechanical experts. If you fully straighten this foot, the heel goes straight up and down, but the correction places too much support under the inside front of the foot (near the big toe). Drs Sheldon Langer, Justin Wernick, and Howard Dannenberg were the first podiatrists to discover and explore how potentially dangerous this support was. Too much pressure under the big toe area (first metatarsal) could block the normal motion of the foot from heel to toe and cause problems in the foot, ankle, knee, hip and back. They coined the phrase "Sagittal Plane Blockade" to describe this problem. When you walk with your orthotic devices, do you feel like you can easily move across them? This is a question I try to ask all my patients, and try to observe in gait evaluation. It is vital for normal foot function and to avoid symptoms.

     When I measure foot biomechanics, and I take a cast capturing over 5 degrees of forefoot varus, I know I will have issues for compromise to deal with. Fully correcting the total amount of forefoot varus would probably lead to problems related to Sagittal Plane Blockade. Correcting less than total could lead to the continuation of symptoms related to the pronation I was trying to treat in the first place. For the biomechanical experts out there, if you sacrifice some of the forefoot varus correction with a modified Root Balance Technique consider Kirby Skives, Inverted Pours, or BiAxial Wedging to get your pronation control without producing Sagittal Plane Blockade. You are basically transferring support from the front of the arch to the back of the arch.

Top 100 Biomechanical Guidelines #42: Root Balancing Forefoot Valgus maximizes Lateral and Metatarsal Support

A Forefoot Valgus Cast sits Inverted on the countertop.

The edge of the box is vertical demonstrating the Inverted heel position of the cast.

When this type of cast is Root Balanced, the lateral column and the metatarsal arch gets great support.

 Positive Cast with Inverted Heel noting forefoot valgus type foot

 Heel is set to vertical before plaster poured into negative cast

 Negative casts being set for pouring

 Once the plaster dries, the cloth is removed. The inverted heel position is seen.

 The forefoot is balanced initially with a nail.

 Plaster is used to make a platform for balancing.

 The platform will make a dramatic lateral and metatarsal arch.

 Here the lateral arch is demonstrated.

Here the metatarsal area is shown lower than the platform, which will make a great metatarsal arch within the plastic.

Top 100 Biomechanical Guidelines #40: Root Balancing possibly damaging with Everted Negative Cast (Forefoot Varus type)

These are Forefoot Varus/Supinatus casts which stand in an Everted Position. When you use Root Balancing Techniques to fully correct, you may produce pathological (harmful) blocking of normal first ray plantarflexion with SAGITTAL PLANE BLOCKADE. You may also produce long axis of the midtarsal joint supination (at a time with the midtarsal joints should be fully pronated for stability). So, whereas Forefoot Valgus support with Root Balancing is sacred territory to fully correct, Forefoot Varus support with Root Balancing is filled with land mines and booby traps. More to come.

Top 100 Biomechanical Guidelines #39: Root Balancing Crucial with Inverted Negative Cast (forefoot valgus/plantar flexed first ray deformities)

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     When I am dealing with patients with lateral foot and metatarsal problems, I love when I find forefoot valgus tilts in their biomechanics. The correction for this everted forefoot tilt allows for Maximum Lateral Column and Metatarsal Support at the same time. The cast of the right foot below shows the negative cast capturing this everted forefoot to rearfoot relationship. When the forefoot has an everted deformity, the negative cast will sit inverted.

Here the casts are brought back to a more stable heel vertical position in preparation for making the postive cast corrections, and eventually, the orthotic devices themselves.

After this cast is filled with solid plaster, it will be leveled to the stable heel vertical position.

See how the lateral arch demonstrated here is just as high as some medial arch supports giving great lateral column support.

See how this lateral arch support will translate into great overall metatarsal support.

Here a little taste of how the process goes at the lab. Once the heel inverted position is noted, a nail is used to bring the cast back to a heel vertical stable position.

 Then plaster is used to make what is called a platform with the end point where the orthotic device (plastic) will end just behind the weigth bearing surface.

 Hopefully, this representation of the foot after the platform is in place shows the potential of great metatarsal support.

 Here the positive cast is placed down with lateral arch in full view. This translates into a great lateral or outside arch.

Here is an orthotic device made off a similiar mold with a inside and outside arch so similiar that it is hard to tell what side is the normal arch. Also, easily demonstrated, is how much natural metatarsal arch is created.

So, here is the magnificence of a Root Balanced Orthotic Device. In the next posts, I will be discussing the pros and cons of the Root Balancing of forefoot varus or supinatus. But, for now, I will finish saying balancing Forefoot everted deformities is the true greatness of the Root Technique. What are some of the problems treated successfully with this technique? These include:

1. Morton's Neuromas
2. Metatarsalgia
3. Tailor's Bunions
4. Bunions
5. Metatarsal Stress Fractures
6. Sesamoiditis/Sesamoid Fractures
7. Cuboid Syndrome
8. Midfoot Sprain/Arthralgias
9. Peroneal Strains
10. Ankle Sprains