Palpating the Subtalar Joint for Neutral Position
Before you start measuring, keep in mind that this is not a precision measurement. You are taking a measurement to determine if you should choose a 3.5mm or 6.0mm insole for your patient. (placing the patient in one group or the other)
Keep in mind that palpating the subtalar joint for its neutral position is a subjective measure and fortunately perfection is not necessary. The best method to determine the STJ neutral position, is motion-palpation: Place your index finger about one inch below the ankle joint (medial malleolus) on the inside of the foot and slightly forward so you can feel the joint. As the patient is supinating and pronating the foot, (rolling the foot out and in) you will feel the joint surface change. Fully supinated, the joint surface almost feels hollow, and fully pronated
you can feel a ridge. The joint is in neutral position when the bones are aligned (the joint surface feels smooth). Sometimes it is simpler to find the neutral position by observing the heel bone being perpendicular to the floor.
It can also be done by trial and error by inserting the micro wedge to the point where the heel stabilizes when the patient does a knee bend.
Measure the First Metatarsal Deficit (FMD)
Measuring the FMD gives you a static indicator of which PCI should be selected for the patient.
The rule of thumb is:
Ground force ˜ FMD X 30% (Pick the insole that measures closest to 30% of the FMD measurement.
Use the micro wedges to measure the FMD. The micro wedges are dimensioned and marked to allow a quick reading of the FMD.
To measure the FMD, ask the patient to stand with parallel feet, 10-12 inches apart, equal weight on both feet. If unstable, have the patient face a wall to stabilize with their hands to stay balanced. Using two micro wedges and motion-palpation, ask the patient to slowly roll the ankle outward as necessary to put the Subtalar Joint (STJ) into its neutral position. When the STJ is in its neutral position, slide the micro wedge under the first metatarsal head and big toe until it meets slight resistance and will not slide further using light pressure. Repeat, using the second wedge, for the other foot. With both micro wedges in place, the feet should remain in the STJ neutral position, and the heels should be perpendicular to the ground.
Use the scale on the micro wedge to read the FMD at the medial edge of the first metatarsal head. Record for both feet. It is normal to find that one foot has a slightly higher reading (deficit) than the other. For the purpose of choosing the PCI, interpolate the readings. Always use the same amount of ground force on both feet.
While the patient is still on the micro wedges, have the patient bend their knees and observe the change in the knee and ankle motion. (Knees should move over the foot, ankles should be straight.)
Make sure to point out this change to the patient, so they can feel and see the difference. Have the patient step off the micro wedges,
do a knee bend, and step back on the wedges again to do another. Most patients will feel the reduction in torque in the ankles, knees and hips. Setting up a mirror in front of the patient allows the patient to visually observe the changes as well.
Be prepared that a few patients do not have a good sense for detecting change so they are less likely to notice, and some patients are so muscle bound, that it may take days or even weeks for the changes to take place. Most people do feel and see a profound change.
It is important to note that the measurement of the FMD is an arbitrary number taken, and that the measurement location was chosen for convenience. The number is only meaningful relative to the standard we have established. Patients measuring in excess of 22 mm, may be good candidates for 9.0mm PCIs, but start with 6.0mm. From 0 to 9.0mm is just too drastic a change for most people. The patient’s first response on the 9.0mm can be that it feels good, but unless they have been acclimatized to a 6.0mm first, they will likely change their opinion after two or three days.
Parallel or Flared Feet and the Effect of Awareness
A majority of people, especially those who hyperpronate, naturally stand with their feet flared. Often the foot hyperpronating the most also flares the most. Doing the measurement and the knee bends with parallel feet is often more graphic, as the patient can clearly see their ankles roll in and their knees moving toward each other and often coming completely together. After inserting the micro wedges underneath the first metatarsal and big toe, the patient will notice how their knees move straighter and remain apart when they do the knee bend.
If the patient does a knee bend while standing with flared feet, it will look like the knees remain evenly apart while in actuality the knees are moving to the inside of the plane of the forefoot.
Until you are ready for the patient to observe, tell the patient that you are looking at the motion of their ankles. Have the patient look straight ahead when doing the first few knee bends. For most people that insures that the ankles and knees are moving freely and naturally. If you tell them that you are checking if their knees move over their feet, the patient will often try to guide their knees because they are now conscious of it.