Flat feet is often seen with patients often coming to the clinic for treatment, showing signs of collapsed arches or overpronating during a gait analysis or exercise screening process,

Custom orthotics and gait analysis in bolton using custom orthotics for flat feet and over pronation
If Planus foot morphology (Flat Foot) is associated with frequent knee pain and medial knee cartilage damage in older adults.
And…
it has been noted Moderate and severe pes planus was associated with nearly double the rate of anterior knee pain and intermittent low back pain in a study of 97,279 military recruits. (ref:below)
How do you know you have it?
Have a Dynamic Gait? utilising a FootScan pressure plate with analytical software to map out exactly how your feet interacts with the floor, demonstrating the weight and contact distribution from initial heel impact to toe off on propulsion, its amazing what 4000 pressure sensors can tell you!..
What do you need to do if you have it?
Sometimes nothing if minor, however if you take part in high impact sports such as football or run you need to address the issues, this will reduce the risk of injury whilst correcting foot motion will improve performance.
Having a Gait Analysis will give you information to take the right action. This may be rehabilitation exercises to strengthen the intrinsic foot muscles whilst addressing any imbalances and adaptations in the knees, hips and spine. The Gait Analysis provides data to produce a custom orthotic designed precisely to your feet to provide support and stability. This combination will provide corrective and preventative actions for a positive outcome to keep you running and loving the sports you do.
Hope that useful
Keep Well, Keep Active
Francis
ref:Kosashvili Y, Fridman T, Backstein D, Safir O, Ziv YB. The Correlation between Pes Planus and Anterior Knee or Intermittent Low Back Pain. Foot & Ankle International. 2008;29(9):910-913.