This is the part 6 of a series that should be read in order.
Key Points:
- The post is on Intense Pronatory Corrections
- The Importance of Measuring OCSP to see if your Correction Ordered is Accomplished
- Effect of Rearfoot Varus on Foot Biomechanics
- Think about common causes of moderate to severe pronation that force the foot to evert to MPP
- What is Dr. Kirby’s MPP test
- In the example given, what would be 3 heel positions considered acceptable and stable positions to achieve with orthoses
- The role of P3 orthotic device giving 6 degrees of correction (3 different but similar orthoses)
- Why is Subtalar Joint Neutrality Ideal for Many Patients?
- How many degrees of correction can be achieved in P4 and P5 orthoses?
- How is P5 achieved?
Anytime you prescribe an orthotic device for a pronatory problem, using simple measurements of RCSP, NCSP, FF/RF deformity, and OCSP when indicated can be an incredible success, and incredibly predictable. However, every year I have a few patients that seem to follow their own rules. Today, we are also going to talk about the MPP test and its importance.
Since you only need to order these various orthotic devices, and not make them, and if you agree to take these 4 simple measurements, I think we are good now to go over another example. However, I also encourage you for this pronation category to come up with 3 versions of the correction desired since your lab may have their own methods. If you are measuring OCSP, you will see if you are getting the correction you ordered.
RCSP 6 degrees everted
NCSP 4 degrees inverted
FF/RF 2 degrees varus
No current orthoses
This is a patient with more pronation than the deformity measured. NCSP 4 degrees inverted means that the patient has 4 degrees of Rearfoot Varus (which pronates the heel due to compensation to heel vertical). The 2 degrees of forefoot varus pronates the heel to 2 degrees everted. Yet, we have a patient 6 degrees everted, or 4 degrees more pronated than it should be based on the FF/RF measurement. We may have to find the possible cause: equinus, MPE, ligamentous laxity, long leg, etc. After you measure RCSP, internally rotate the whole limb being measured by rotating at the hips, and not lifting the foot off the ground laterally. Or, use Dr Kevin Kirby’s method, and while in RCSP, fire the extensor’s to the 4th and 5th toes in an attempt to lift up the lateral forefoot. Now, remeasure the RCSP. This is called the MPP or Maximally Pronated Position. This is our next important measurement. In this case, the RCSP and MPP were both equal at 6 degrees everted. We have therefore a foot functioning in its maximally pronated position. This foot is far from subtalar neutral, typically in a malaligned position, functioning as a flat foot, and functioning with no shock absorption ability.
How should we look at all of this? Achieving a certain degree of stability is initially accomplished with any orthotic device by inverting the heel 2-3 degrees from its MPP. So, if I make an orthotic device by any means (B1 or B2), and my OCSP is 3-4 degrees everted, I have done a decent job. Many orthoses with decent medial arches, slight medial Kirby, deep heel cup, good width and foot shape will accomplish this. The patient feels very stable, but that is always a great question to ask them about their orthoses, new or old. When you can get them out of MPP, joints throughout the lower extremity do not hurt so much.
This 2-3 degrees inverted from MPP is an improvement, and you may be getting there accidentally if you are not measuring, but this is not a perfect scenario. Therefore, for this patient, OCSP of 4 degrees everted is acceptable. I am 2 degrees inverted from RCSP and the MPP. This is typically accomplished with P1 orthos (providing up to 4 degrees of pronation control, and definitely will pull you away from MPP). Yet, everted heels with inverted NCSP need at least to get the heel to a vertical position in my mind. Vertical is not subtalar neutral, but a much better position than being everted. Since our RCSP is 6 degrees everted, we need 6 degrees of pronation control now. P3 gives 6 degrees on average, so what do we need to prescribe for that? We can use a 25 degree Inverted Orthosis with a deep heel cup and wide athletic frames. We can also use 15 degrees Inverted with 4 mm Medial Kirby. We can use B1 to balance the FF/RF Varus of 2 degrees, add a 3 mm Medial Kirby, and 3 degree varus RF and FF posting. We can also go with the maximal 5 degrees of RF/FF varus posting with 2 mm medial Kirby skive. If you measure your OCSP, you will never go wrong, and you can experiment for the desired results with the techniques your lab can provide for you.
The 6 degrees of inversion setting the heel back to vertical is an excellent Rx, but shy of subtalar joint neutrality by 4 degrees more. Subtalar neutral is so ideal for so many lower extremity problems, especially the ankle and knee. This is where the lower extremity is stacked up perfectly for this patient. There is minimal tension in the ankle, an even pull of all the muscle groups. We will need a P5 to get there. And, I don’t recommend it initially. For this case, and so many cases, my starting point is P4 giving 7-8 degrees of change. A 7 degree change at the foot is almost a ½ inch (7/16) change. It can be difficult to get used to, or adapt to. This is my initial starting point for cases where I may have to go more than 7 over time. For this patient, it is 10 degrees to subtalar neutral from RCSP. This is too much change to go all at once. Yet, after 3 months of consistent wear of a P4 insert, progressing to P5 is normally tolerated well. You have to advise your patients of this when you are starting the process due to the multiple visits and the added expense of an additional device months later. It is simple math by comparing RCSP to NCSP, prompting the additional subsequent orthosis with sequentially more correction.
P5 will give you 9-10 degrees of pronatory support to hold this foot in subtalar neutral. I agree also with the majority that 2 degrees on either side of neutral is typically satisfactory except for a few exceptions. Therefore, if I want to place this patient in subtalar neutral, attaining 6 degrees of varus support to 2 degrees Inverted should be fine. You also need to compare OCSP to gait findings and the patient’s subjective comments.
How is P5 accomplished? So, this patient started out with a 10 degree difference between RCSP/MPP and NCSP. It is too much to simply ask our FF varus correction of 2 degrees even when we put less arch fill and thicker plastic to make more of 3-4 degree change (and yes, I talk to my orthoses and tell them what I expect with each patient, but only when I am alone). I hope that you can see how 5 degrees of forefoot varus captured in our image and then fully supported with Root Balancing would have been better to support and make more inversion moments. All of the 10 degrees needed by subtalar joint control to create supinatory moments on the medial heel and proximal arch has to come from various forms of rearfoot control. I routinely use a 35 degree inverted orthosis (7 degrees of correction) with a 3-4 mm medial Kirby skive (2-3 degrees of correction). We could also use a 25 degree Inverted with 4 mm medial heel skive and 3 degrees of extrinsic rearfoot and forefoot varus posting. Yet, thicker than normal plastic, Kirby skives, inverted intrinsic pour, extrinsic forefoot and rearfoot posting, and stable shoes can get us close and very happy.
I will talk about this further in later posts, but rearfoot control was not a big part of Root Biomechanics in the 1970s. Before you get mad at me, you have to remember that forefoot balancing was what revolutionized the world of biomechanics outlined by Dr. Root, et al, and has helped millions of patients around the world. Dr Root did believe rearfoot stabilization with rearfoot posts was needed sometimes. What we heard from many biomechanists was that rearfoot control was useless, and only propulsive phase stability with a good active propulsion was important. Islands of good thought from Richard Schuster in New York, Kevin Kirby, Richard Lundeen and his Bi- and Tri-Axial Orthoses, and others, kept the concept of the importance of rearfoot control. With the running boom, varus wedges are incorporated into both shoes and orthoses routinely. Next post, I will comment more on the effect of forefoot valgus vs forefoot varus on pronatory control.
Review of all the Orthotic Types Being Presented
Corrective Orthotic Devices
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- 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
