Why do flat feet make people more prone to stress fractures?

Micro trauma to bone: Flat feet is a condition in which the arch of the foot collapse, causing the foot to be contact with the ground .With repetitive usage , esp with runners, it causes muscles to be fatigue, in turn put stress to the bones which can cause stress fractures..

Increased pressure: Flat feet cause abnormal pressures on areas of the foot not designed to handle increased load during weightbearing, metatarsal stress fractures are the most common particularly the second metatarsal- as the foot flattens, or pronates, load is shifted from the first metatarsal to the second potentialy over time causing a stress fracture.