In the definition of fallen arches that is part of this web site, I see that lax ligaments are the most common cause. I'm pretty sure it is in my case, as I also have double jointed knees (knees lock so far back that my legs are not straight, but curve back). On other websites which explain the origin of flexible flatbook, I have also seen it attributed to a tight achilles tendon (heel cord). Is it one or the other or both? What is the relationship between the achilles tendon and the arch? It's hard for me to imagine that a tight heel cord would create a flexible flatfoot . . . If so, does it help to do stretches so that the achilles tendon is less tight?

I am asking because I injured my left foot a year ago september and having a really hard time getting effective treatment (ie., treatment that helps rather than making the pain worse). In fact, after 9 months of living with a pttd diagnosis (posterior tibial tendon dysfunction/partiial tear) and 7 months of using orthotics which were supposed to treat that condition (they have done the opposite), it now turns out (with a better resolution mri, and more attentive clinical examinations) that this was a false diagnosis. Unfortunately, the doctors (i've seen many, including several foot and ankle specialist mds) do not know what the problem is. So i'm trying to find out more on my own as no one i've seen thus far has been able to help me.

Thanks in advance for any help with my question or the larger problem. I'm trying to find other people who have been through or are going through similar foot sagas.