In my last post (Part 1: Why use functional foot orthotic devices?), I boldly implied that using a good lab and taking a good impression of the foot, typically helps patients both gain stability and feel more comfortable. Since you will cast alittle differently than me, and order your Gold Standard (standard Rx for patients) differently than me, yet we both are happy with improved stability and improved comfort of our patients. This has been accomplished on the backs of Dr Merton Root, Dr John Weed, Dr William Orien, Dr Richard Schuster, Dr Joseph D'Amico, and so many more who both improved biomechanical knowledge and adapted that knowledge to the orthotic laboratory. We all can thank our leaders for a slow, but rewarding, progress of the last 70 years. In podiatry, the progress has been meaningful, and should continue. I implore doctors to be more mindful of the process from cast or impression, to dispense, to followup. Who are the patients where things are not quite right? What are the injuries that biomechanically you are struggling with helping? This may be different in our sports medicine doctors working further up the leg to the back in some cases.
For this post, let's talk about subtalar neutral and its importance. You have learned when the subtalar joint is in neutral there is even pull medially and laterally across the ankle. Definitely, if I can place all of my athletes for their repetitive motion activities in subtalar joint neutral, I am happy. I know the pull medially and laterally is even. I know that the posterior tibial is not in a disadvantaged position when the subtalar joint is too pronated, and that the peroneal tendons are not overstressed when the subtalar joint is in a supinated position. I know that the achilles in pulling only in the sagittal plane as it is meant to and not twisted. I know that the tarsal tunnel is free of compression forces under the lacinate ligament. I know that if I can keep the muscles strong in the ankle, and the achilles in its right flexibility, I have a sound ankle. The more structurally true the ankle is, the less injuries or pain syndromes it develops. This is why subtalar neutral should be a goal, sometimes very attainable, of your patients. And yes, the subtalar joint is not fixed in neutral with foot orthotic devices, like a rigid AFO. Yet, keeping the subtalar joint in a happy zone of 3-4 degrees on either side during activities, gently moving back and forth in this inversion eversion range, will not allow pathology to develop. You will be helping the patients weak spots. You will be allowing them to live healthier lives. Remember, the above discussion really only applies for repetitive motion activities like walking, prolonged standing, hiking, running, biking, and downhill skiing. Yet, the same principle of subtalar neutrality has been used for centuries by the French in their ballet dancers, and many other activities.
I ask again that you review the post on RCSP for heel bisection tips and measurement. Like RCSP, NCSP is a standing measurement with the ground as our reference point. The patient stands in their natural angle and base of gait with the knees extended and equal weight on both feet. The posterior surface of the calcaneus typically has been bisected, but skilled providers can bisect the heel standing. You are bisecting the heel bone itself and not the soft tissue. You then measure the degrees that the heel is everted or inverted to the ground. This is your RCSP and means alot in our understanding of lower extremity biomechanics and Rx writing. From this position, you place each foot, one at a time in neutral subtalar positioning. This position is found with palpating the medial and lateral sides of the talar neck, and developing the skill to know their position to your hand is equal. You have the patient invert their foot while feeling this position, and then evert their foot while feeling this position, and typically after 3 or 4 inversions and eversions you can place the patient in a position of subtalar neutrality.
Here I am palpating non-weight bearing, but easily done weight bearing
When you then look at that foot, the ankle looks perfectly aligned to the heel. When you tell the patient to stand still and not move, you can go around to the front of the patient. Here you can check two things: (1) the heel and ankle appear perfectly aligned, and (2) the tibial crest if marked is in alignment with the 2nd metatarsal if also marked.
Again, this is non-weight bearing, but subtalar joint neutral is where the tibial crest is in line with the 2nd metatarsal.
You have achieved Subtalar neutral and you measure the heel positon to the ground. Like RCSP, NCSP (neutral calcaneal stance positon) can be inverted, perdendicular, or everted to the ground. You define your rearfoot deformities of rearfoot varus or valgus from this measurement.
The above image is of NCSP left foot where the heel is perpendicular to the supporting surface
I love this image when I discuss subtalar neutral. And, I always tell my students to observe first and measure second. Here the right side is close to neutral subtalar joint (you have to image the lower tibial bisection line), and the left side is pronated from neutral. This patient is in RCSP on both sides with NCSP 7 everted bilateral. However, only the left pronated from neutral in RCSP.
Here is another patient with subtalar joint neutral position found on the right (and NCSP right was close to 0 degrees or perpendicular). The left remains in her RCSP pronated from neutral and everted to the ground.
This patient had significant genu varum and tibial varum. The neutral position of both subtalar joints were both inverted. The RCSP (shown here) was pronated slightly from neutral and still highly inverted left greater than right. The patient had approximately 4 degrees STJ eversion range of motion, and less than 10 subtalar inversion range of motion.
In summary, and before I get too long winded, obtaining subtalar neutral can be crucial to attain with your biomechanical skills for a patient with certain symptoms. Not to be vague, but the key here is being knowledgeable about where a patient functions as they get symptoms and can symptoms be changed by one of our positions of stability. These were: 1) 2-3 degrees from MPP, 2) heel verticality, 3) subtalar neutrality, or 4) some centering position not too pronated and not allowing contact phase supination. And there are some patients where my orthotic devices achieve all 4 at once. This represents where we try to place patients with our inserts. As you treat patients, it is your experience which will decide which position is best to achieve at a certain time. More on this in another post as we talk about changing patient positions, and I will use some of the above images. For now, just understand, that being able to understand an indivividuals RCSP and NCSP can be vital to their treatment (and relatively easy for you to accomplish). And, please understand, there are thousands of patients who would not have gotten better if the goal wasn't directed into achieving subtalar neutrality.
