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Originally Posted by Scorpio622
What is the best shoe to recommend for individuals with frontal plane instability of the STJ and/or ankle? I have been recommending a tennis shoe over a running shoe with the assumption that the running shoe is designed primarily for sagittal plane function and the tennis shoe is designed for more lateral movements (hence more lateral stability). Any thoughts???
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This has been developing into an interesting thread and I would like to offer some thoughts. First of all, like Eric Fuller noted, let's try to define stability and instability relative to the foot.
Foot Stability: A mechanical property of the foot where it is able to resist rotational or translational motions when it is subjected to external forces.
Foot Instability: A mechanical property of the foot where it is unable to resist rotational or tranlational motions when it is subjected to external forces so that either gait abnormalities or pathologies occur.
One way to quantify stability would be to use the concept of
foot stiffness, relative to movement in one body plane. For example, if you were to take and measure the external load vs deformation applied to the STJ and MTJ for frontal plane motion of the foot relative to the tibia, you would come up with a load vs deformation curve where stiffness could be measured and this could be done both passively, without muscular contraction, or actively, with muscular contraction resisting that motion.
When an individual walks or does other weightbearing activities in shoes, then the shoe may either make the foot more stable or less stable within the frontal plane, depending on the design characteristics of the shoe. It is important to realize that even a stable foot can become unstable in the wrong shoe and that a very unstable foot can be made to be very stable given the correct shoegear.
The design characteristics of a shoe that will tend to decrease frontal plane instability of the foot are the following:
1. High top upper made of relative non-deformable material (high stiffness) with the higher the upper and stiffer the material, the greater the stability. To maximize STJ stability, the upper must be above STJ axis, preferably covering the malleoli.
2. Decreased sole thickness to decrease height of STJ axis from the weightbearing surface.
3. Increased sole durometer to decrease medial and/or lateral deformation of sole of shoe (i.e. frontal plane tilting of sole) under weightbearing loads.
4. Increased medial to lateral width of shoe sole to increase medial/lateral lever arms across STJ axis.
5. Firm binding of upper to the sole to increase frontal plane stiffness of upper of shoe relative to sole of shoe.
Tennis shoes, racketsport shoes and fitness shoes tend to have increased frontal plane stability relative to running shoes. The thinner and harder the sole, the better. However, having a high top boot does help also, but as mentioned by others, does not allow for good ventilation of the foot. I have had some patients take their boots and have holes punched into the uppers to increase ventilation which greatly helps decrease the perceived heat of their foot.
I tend to use ankle braces in low top shoes for many of my athletic patients with STJ/ankle inversion instability. Alternatively, I teach them how to tape their ankles, which is often more effective and comfortable than braces, but more expensive in the long run.
In any way, one needs to understand the mechanics of the ankle/STJ in order to understand frontal plane instability. As Eric Fuller stated, if you don't know about lateral deviation of the STJ axis, then you are missing out on a significant cause of lateral ankle instability within the population. Maybe Craig Payne can tell us about his study that showed that all of the subjects he tested with asymmetrical ankle instability had decreased supination resistance with his supination resistance apparatus.