pyrrura molinae

Hello, I'm Dario
I've a parrot ( pyrrura molinae hypoxantia ) for 2 years.
For 8, 9 months I've noticed that he has some problems ( that I didn't
notice before ) with his paw.
He has difficulty to open or close the paw and when he climbs up the trestle
one of his legs remains close as a fist and often he losts his equilibrium
and falls down.
Also when He walks he strumbles cause his paw is not good open to have a
good grip to the barriers of the cage.
I didn't have idea of the problem and I hope you can help me.
I'm sorry but my English is not so good, I know, but I'm not English!

Thanks,

Dario