pies planos => flat feet en
http://www.wordreference.com/es/en/translation.asp?spen=pie

http://www.vegsource.com/articles/guest34.htm
"High heels, overly tight or worn down shoes, and shoes with inadequate arch support can all distort the foot's natural form. With this tightening of the tendons and muscles, your feet eventually become *** unbalanced and unstable. ****
When the three pads on the bottom of the feet (ball, side, and heel) are no longer fully or evenly touching the ground, *** instability
results ***. *** Unbalanced feet *** can lead to a misalignment of your entire body, creating muscle tension. This tension can be the cause of leg pain, lower back pain, neck and shoulder discomfort and even headaches."

Un saludo.