Adult-acquired flat foot is a painful and progressively worsening condition that causes foot pain and dysfunction in sufferers and can make standing and walking unbearable. Adult-acquired flat foot is caused by a breakdown and weakening of the posterior tibial tendon, an important tendon for stabilizing the foot's arch. As a result, the foot's arch gradually collapses, causing a flat foot that splays outward when walking -- over time causing pain due to pinched nerves and wear and tear on joints.

A study published in Annals of the Rheumatic Diseases found that the posterior tibial tendons of those with adult-acquired flatfoot had an increased amount of proteolytic enzyme activity. This type of enzyme breaks down protein - part of the tendon's collagen structure - and is one possible biochemical factor at play in chronic tendon weakening. Authors of the study noted there is a similar increase in proteolytic enzyme activity  in other painful tendon conditions, such as Achilles tendonitis and suggested that this finding may help with the formulation of new drug therapies in the future.

By Catherine Moyer, DPM, About.com Guide