I want to stay focused on my last student image from Part 3, but turn out attention to student 4. We were talking about achieving subtalar joint neutral statically when we can in repetitive motion activities to achieve a solid ankle. Most of the time this is easy to do when you understand where the patient is, and then how to get them there. Let's discuss this student's measurements before and after orthotic devices from the below slide.
RCSP was 8 everted right and 6 everted left. From the MPP, neither foot was in its maximally pronated position (very good). Remember these are young Podiatry students which most likely with continue to collapse into further pronation as they age. This means that most adults that get 6-8 degrees everted, will collapse to their point of maximum pronation, or sublux further as an adult acquired flatfoot.
NCSP was inverted both sides so we are talking typically of a Rearfoot Varus foot type with Tibial Varum. The NCSP was 6-7 Inverted right and 4-5 Inverted left. The compensation for tibial varum, a strong frontal plane force, is heel eversion or foot pronation to heel vertical. Therefore, something was forcing the foot past vertical, another pronatory force. Can you name the typical pronatory forces that may allow a Tibial Varum to pronate past vertical? Some of the common ones to look for are: forefoot varus or another inverted forefoot deformity, metatarsus primus elevatus, ligamentous laxity, equinus, or internal tibial and/or femoral rotatory issues. With these deformities, the pronation can be to the end of the eversion motion of the subtalar joint.
With cases like these, with these simple measurements we are classifying our patients well. I wonder why RCSP is not equal to MPP, but the measurement seems to be accurate with 2-3 degrees. So, they sort of match up. I know when measuring the MPP, after measuring the RCSP, we have the patients maximally internally rotate the lower limb and they may overdo it with more genu valgum produced. This may be why Dr Kevin Kirby prefers to just attempt to pronate the foot further with his version of MPP.
In summary of student #4:
RCSP Right 8 everted
NCSP Right 6-7 inverted
RCSP Left 6 everted
NCSP Right 4-5 inverted
Now for the OCSP at orthotic dispense 2 weeks later:
OCSP Right 0 or Heel Vertical
OCSP Left 6 inverted
When prescribing for this patient, his tibial and genu varum meant that he pronated, but had a lateral instability component. This would be the same with an severe pronator that had unstable lateral ankle ligaments, or an intoed gait, or broken down shoes to the outside. He also had hypermobility in the subtalar joint with over 40 degrees total range of motion (when 30 is normal). These patients have to be studied more, and I have had nice talks with Dr Mark Warford about them. His particular patient was presecribed 7 degrees of correction right and 6 left and his OCSP to RCSP differences was 8 on the right and 12 on the left. The right responded normally, but the left too much (6 more degrees than prescribed).
I had alluded to the importance of measurements and we should add Subtalar Joint Range of Motion or Excursion to our top list. The numbers are important, but the simple classification of a hypomobile, normal, and hypermobile joint is fabulous. These 3 classifications of the normal speak volumes on how the foot responds to the ground. Subtalar joint range of motion is so easy to measure, and there are different techniques. Here are some examples of measuring subtalar joint range of motion with the tibial bisection and your reference point, and the heel bisected in open kinetic chain.
Measuring subtalar joint range of motion is typically how I define a hypermobile foot vs a hypomobile foot. Here subtalar joint eversion is being measured with the tibial bisection being the reference point.
In Part 5 of this series, I will begin to talk about supinators. But here, I need to evaluate my new OCSP. The right side was heel vertical, which is stable, but not at subtalar neutral. Do I need to increase correction to neutral. What are my symptoms? Would subtalar joint neutrality help? On the left, the patient is now in subtalar neutral statically, but definitely had dynamic lateral instability. I added a Denton modification, and narrower the medial side of the orthosis and removed the medial side of the rearfoot post. This eliminated the lateral instability.
I hope this discussions around RCSP, NCSP, MPP, OCSP, and subtalar joint range of motion help. See you next week. Rich
