Hi William
The HP nurse is not qualified to diagnose that you have osteoarthritis and nor is it the point of an assessment. They may have put down incorrect information. You say that this has been used to deny you a mobility award. I assume the assessor did not think that your mobility was restricted by your osteoarthritis enough to meet the PIP criteria. If you wish to challenge this, you can put in for a mandatory reconsideration although you will have to put in for although it will be a late request.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
