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Friday, March 15, 2019

For Podiatrists: Biomechanical Discussion Points #1

This is the first of hopefully many blog posts under the label of Bio-mechanical Discussion Points that has been sparked by the wonderful books from Dr. Kevin Kirby. 

Bio-mechanical Point #1: In what position of the heel are the patients most stable: is it heel vertical, heel inverted, or heel everted?  

     The best heel position for stability depends on several factors. One concept was first introduced by the ballet world in the 1700's that the most stable position of the heel is when it is stacked directly under the talus, and the talus is stacked directly under the tibia. I have always found that patients, and especially dancers (who are very attuned to their bodies), can feel this inherent stability. This has been termed the neutral position of the subtalar joint (neither inverted or everted) from that position, much as the neutral position for stability of the ankle joint is where the tibia is at a right angle to the foot (in which the ankle is neither dorsiflexed or plantar flexed from that position). 
     That stable subtalar joint neutral position is inverted to the ground when we have tibial varum and other forms of rear foot varus. That stable subtalar joint neutral position is everted to the ground when we have tibial valgum or other forms of rear foot valgus to treat. Therefore one person can be in their most stable heel position to the ground 5 degrees inverted and another person 5 degrees everted. The most common will be tibial or rear foot varus that will set the ideal heel position to the ground somewhat inverted. Too often orthotics are set at vertical for these patients meaning that the orthotic holds them pronated or everted from their most stable position, which means makes them more unstable. If we measure these positions, or at least recognize these deformities by observing the patient in angle and base of gait, we can be more thoughtful in prescribing an orthotic device's heel position. 
     When does this thought process get thrown out the window? All the time. Patients present with certain needs that may have higher priority than simple Root Bio mechanics (not that there is anything simple about Root Bio mechanics). This need may be permanent or temporary, but must be addressed. What are some examples? A patient presents with terrible pronation due to a high degree of tibial varum (bowlegged) mechanics, but they have had 3 ankle sprains and are trying to avoid ankle reconstruction. Root Bio mechanics would have them Inverted due to a high rear foot varus, but their injury with lateral instability requires a vertical heel pour or even slightly everted if they have the range of motion. The goal of the orthotic device, which may change down the line, is for elimination of the supination forces, not correcting the abnormal pronation. This is so common in a sports practice. 
     Another example which is very common in my practice, almost daily, concerns lateral wedging for medial meniscal at the knee problems. If you pronate the foot for a period of time, and open up the medial knee joint line, you can let an injured meniscus have time to heal. You are not concerned about the ideal heel position for stability, but only to generate enough pronatory force to off weight the medial compartment of the knee. This can be extremely important in documented medial knee compartment issues 50% of the time. The other 50% actually want more stability, and you may be inverting the heel to give them that. Inverting the heel 3-5 degrees in general, stabilizes the medial knee compartment, places more weight on the medial knee compartment, helping so many soft tissue medial knee torque or instability problems. 
     I hope to keep the thinking going. Thanks for reading. Rich

1 comment:

Thank you very much for leaving a comment. Due to my time restraints, some comments may not be answered.I will answer questions that I feel will help the community as a whole.. I can only answer medical questions in a general form. No specific answers can be given. Please consult a podiatrist, therapist, orthopedist, or sports medicine physician in your area for specific questions.