It could be an undiagnosed tarsal coalition.
In recent months I have had several children present with markedly painful flat feet that have been treated unsuccessfully for many years solely with orthotics. Upon in-depth investigation, aided by medical imaging, it became apparent that each of these cases involved undiagnosed tarsal coalitions.
Correct diagnosis, followed by excision of the coalition resulted in a full recovery in each case.
When assessing patients with painful flat feet, if the foot, and particularly the rear foot, is fixed or rigid and non-reducible it could be a sign that something more complex may be present. Radiographs, and possibly also an MRI or CT, are required to determine if a tarsal condition is present.
If you are a podiatrist and suspect one of your patients may have a tarsal coalition, or if you would like to find out more about how quickly and easily the condition and resulting pain can be resolved, please feel free to contact me.