Most of us were barely in kindergarten when Dr. Merton Root began to revolutionize the biomechanics world, much like Copernicus telling the world the Earth moved around the Sun. One of Dr. Root’s contributions that was quite revolutionary was that an inverted heel could be pronated. This shocked the world that was heel vertical fixated defining problems related to its relationship to the ground. Back then, and even some today, believe an everted heel is always pronated and an inverted heel is always supinated. He talked about problems related to pronation in general, and how an inverted heel at times presented with these pronation problems. Dr Root et al took the position that the heel verticality is not the object of treatment, but subtalar joint neutrality is. Dr Root explained the patient can be a severe pronator and have their heel inverted to the ground, vertical to the ground, and everted to the ground. Wow! In addition, you could be a supinator with all 3 also occuring. It was all about the position of the subtalar joint in its neutral position. In the biomechanics world, this is as shocking as Bruno’s statement that the world is round, not flat. I feel sad for Bruno, burnt at the stake for such a statement. But, I digress.
Here is where our measurements are needed, at least observations of a patient standing in a relaxed position and then placed into subtalar joint neutral. This defines the patient’s rearfoot deformities (if any), and their possible compensations. I always want to measure RCSP, NCSP, MPP, and OCSP (when orthoses are available). They all require that you bisect the heel (normally in a prone position), and then stand the patient upright. I advise the patient to march in place and establish their normal angle and base of gait. Now you are going to measure the heel bisection in the four positions mentioned above. First, you measure the heel in its relaxed position (RCSP). Second, you measure the heel position after placing the subtalar joint in its neutral position (NCSP). Third, after allowing the heel to relax, internally rotate the limb one side at a time without lifting the lateral side of the foot (MPP). Or, from RCSP (as described by Dr Kevin Kirby), fire the extensors in an attempt to lift the lateral side of the foot off the ground (also MPP). And fourth, if there is an orthotic device present to evaluate, measure the relaxing heel sitting on the orthotic device (OCSP). Now, let’s look at the typical pronator/supinator with medial/lateral instability using these numbers.
The patients with genu valgum or genu varum are the prime suspects for this biomechanical problem. These 2 deformities combine for 18-20% of the population and both have higher rates of developing knee osteoarthritis than patients without these deformities (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7927531/)
Being a podiatrist for a primarily orthopedic group, my practice has been filled with these patients for 40 years to help their knees through something I could insert in their shoe. The classic approach of varus wedging lateral knee joint pain, and valgus wedging medial joint pain tended to work 40% of the time. This approach was the orthopedist’s expectation from me. My initial visit wedging into varus or valgus tended to be ¼ inch (4 degrees) and a one month follow up. If I attempted to hold their feet near subtalar joint neutral, my success rate rose in the 60% that were nonresponsive to the first attempt. Imagine when I would follow the general rule of wedging for these scenarios:
- Genu Varum with lateral knee pain and application of varus wedge
- Genu Varum with medial knee pain and application of valgus wedge
- Genu Valgum with lateral knee pain and application of varus wedge
- Genu Valgum with medial knee pain and application of valgus wedge
If you think about the general mechanics of these 2 knee deformities, genu varum should be helped by valgus wedging and genu valgum should be helped by varus wedging, then my success rate should have been around 50%. But, there are times when varus wedging helps genu varum and valgus wedging helps genu valgum (and I found paying attention to subtalar neutral was very useful).
The image below is only a stick figure of bowlegs or knock knees. Interestingly, the foot is in subtalar neutral. In both cases, the image shows that the foot does not compensate but neatly stays in subtalar joint neutral. In reality, the varus forces of genu varum and high tibial varum, will force the foot to pronate through the subtalar joint, lessening the inverted angle we see in the image. Yet, with genu varum there are high lateral stress and lateral foot overload. Give a patient with genu varum an orthosis that does not stabilize the lateral column or slightly broken down shoes on the lateral side, and they become supinators. The same is true for genu valgum with tibial valgum. Here there is high medial foot overload which can “let the dam break” with the foot collapsing into severe pronation. Yet, so many patients with genu valgum are severe supinators with subtalar joint compensation. This compensation is easy on the foot to accomplish, since the medial overload on to the foot is like a highly inverted orthotic device, thus creating significant supination moments. I typically see patients with genu valgum striking the ground with the heel everted, and evert some more needing varus support. And, I see patients with genu valgum strike everted, and invert their heel with subtalar joint motion.
My goal with all of these patients is not wedges of varus or valgus, but individualizing their treatment around subtalar joint neutral as our image below represents. This where their alignment is perfect, and the medial and lateral stresses through the foot/ankle/knee are even. Next week I will discuss how to try to accomplish this with our technology available.
