It needs to be rigid when you’re standing on it

It needs to be rigid when you’re standing on it, and it needs to be flexible as it strikes to the ground, so it can absorb the shock forces and the weight bearing forces as it strikes the ground. These static restraints such as the ligaments, as they start to weaken and the foot starts to collapse, you start to overwork or atrophy some of the dynamic restraints, the tendons that are trying to stabilize the foot along that axis of balance, and the axis of balance becomes disrupted. I put this slide up here to show you a relatively well aligned foot in this patient. Her left foot is widened out here, but essentially there is the center of her calcaneus and that weight bearing axis runs between the second and third metatarsal. On this side where she has a very severe flat foot, here is her hindfoot, we sort of estimate that here is about the center of the calcaneus, and you see if you draw that straight line, the axis of balance is shifted. Pretty much now all her metatarsals now shifted out laterally, as she is adducting through this talar navicular joint. You can imagine structures over here become lax, both the tendons and the ligaments, structures over here become contracted. So now, you have the axis of balance disrupted and now you have further forces that are acting to contribute to worsening of the deformity. Foot posture – it is very important to get weight bearing x-rays, nonweight bearing x-rays of the foot, and even later when we get to the ankle, x-rays can look very normal of the foot when you are not standing on it, and a lot of pathology and malalignments come out when you get those weight bearing views. Again, I tend to think of foot posture into three different situations, pes planus valgus of the flat foot as demonstrated in the slide here, essentially, this person had no arch, or their mid foot bones are essentially touching the ground instead of being a good 2 cm up and off the ground, versus a high arch foot, a cavus foot, and then the standard neutral or balance foot, which we call plantar grade.

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