This is the part 7 of a series that should be read in order.
Key Points:
- Case Presented with Severe Pronation in a Forefoot Valgus (Everted Forefoot Deformity) Foot
- ASIS approach to correction discussed
- Correcting Forefoot Varus Feet helps Pronation Control
- Correcting Forefoot Valgus Feet mainly helps Supination Control
- What happens if we don’t correct the FF Valgus in a pronator?
- If I balance a 10 degree FF Deformity, or set the cast 10 inverted in ASIS corrections, what is the standard heel change to be measured in OCSP from RCSP?
- Explain how ASIS pouring may enable you to achieve high inversion correction without using the Inverted Orthotic Technique.
I will continue my discussion on the P or Pronation Orthoses with another example, which provides more nuisance.
RCSP 3 degrees everted
NCSP 7 degrees inverted
MPP 3 degrees everted
FF/RF 6 degree valgus (measured and captured in the scan)
When you take a negative neutral suspension cast of a forefoot varus foot, the positive cast uncorrected will sit with an everted heel (image attached). The shape of the cast is the ideal foot (subtalar neutral with midtarsal joint(s) maximally pronated), but when you balance this cast out (set it to vertical), you are now putting an inversion force of so many degrees on the heel thus helping with pronation correction. The opposite is true with forefoot valgus feet. To correct a forefoot valgus foot by setting the heel to vertical, you must place an eversion force of so many degrees upon the heel, thus negating supination tendencies, not pronation tendencies. Now, you are technically making a very stable orthosis, our Balanced or B1 orthosis, however you are not helping a rearfoot pronation issue, at least directly, with forefoot valgus balancing. You have made a stable impression of the bottom of the foot, but now you have to tell the lab what to do for the desperate need of up to 10 degrees of rearfoot control between the measured RCSP and NCSP. And, remember we have four possible positions of stability we can choose to accomplish:
- ASIS (balance just as the foot sits) ** discussed in detail below
- Balanced to Vertical with full Forefoot Deformity Correction (classic Root B1 device)
- Heel Corrected 7 degrees with Rearfoot Correction of P4 getting us to 4 inverted (previously discussed) This is the only one used in B2 devices (shape based imaging)
- Heel Corrected for 10 degrees using P5 device (getting the foot close to NCSP)
So, in this patient, if we want to invert the foot towards more its NCSP, we would not attempt to correct the forefoot valgus (actually any of the everted forefoot deformities) at all. I have found 2 methods above to help considerably: ASIS presented here, and Inverted Technique P4 or P5 (which both ignore the FF deformity) work well in this case. In fact, the positive cast is balanced in this cast ASIS (meaning 6 degree inverted heel) due to the everted forefoot deformity of 6 degrees. See the image attached. This method of inverting or everting the heel around a neutral positive cast is not 1 degree for one degree change when we measure the OCSP, yet it is widely used, and first proposed by Dr Michael Burns of Burns Orthotic Laboratory I believe. When I use this technique, my heel correction seen in OCSP is anywhere from 1 degree change per 1 degree correction, all the way to 1 degree change per 4-5 degrees correction (much like the correction seen in the Inverted Technique). The standard of correction expected is 2:1, 2 degrees of correction for every 1 degree of change expected. But, you can document the change (OCSP) and just keep moving in the direction that you want to go. Root Balancing to vertical will not achieve my goal of the heel more inverted near neutral. My next post will discuss this.
Let’s see if this makes sense. Using the 2:1 rule above, with the 6 degrees of forefoot valgus setting the non-corrected cast to 6 degrees inverted, I would typically see the RCSP go from 3 everted (RCSP) to vertical (therefore a 3 degrees change for 6 degrees measured or a 2:1 correction). Here you are simply setting the position of the foot inverted the same amount of the everted forefoot deformity. You can see the attraction to this concept. Very easy for the lab to do! You are still capturing the shape of the foot in a neutral subtalar joint while providing an inversion force. If I actually want to invert the heel from 3 everted (RCSP) to 7 inverted (NCSP) or 10 degrees total, I then make the positive with 4 mm medial Kirby skive, and extrinsically add a 4 degree rearfoot and forefoot varus post. With our 2:1 calculations, I would have achieved 3 degrees of inversion moments intrinsically with the ASIS pour, a further 2-3 degrees with my Kirby skive, and 4 degrees extrinsically with my varus posting. OCSP was 6 inverted, therefore I had asked the orthotic device to make a 10 degree change from RCSP and I achieved 9 degrees. Very good! I am happy when I find that my corrections may be too much , and I have some extrinsic posting that I can remove during an office visit. Here ASIS pouring enabled me to avoid the Inverted Orthotic Technique which some labs may not be able to do.
If I went straight with an Inverted Orthosis, I would ignore the forefoot deformity completely. Start with a 35 degree orthotic device (for 7 degrees), and now the OCSP will range from 2 to 5 inverted from an RCSP of 3 everted. This is a good starting point, and if we get to 5 degrees in a stable shoe, we are at that magical 2 degrees from neutral. This 7 degree correction is the highest I like to start with and I have to tell patients that another orthosis is coming down the road with additional expense. I say this, but this example is from my medial/lateral instability patients that can be more complex. These patients will be discussed soon.
Review of all the Orthotic Types Being Presented
Corrective Orthotic Devices
↓
- Balancing (B): (B1 and B2)
- Pronators (P): BP, P1, P2, P3, P4, P5, and P6
- Supinators (S): BS, S1, S2, S3
- M/L Instability (M): BML, ML1, ML2, ML3, ML4, ML5, and ML6
- Shock Absorption (C): BC, C1/C2, C3/C4/C5, C6, and C7
- Sagittal Plane (H): BH, H1, H2, and H3
