Why can't a straighten my finger?

[Iona29]

Hi. About two years ago I broke the knuckle between my right pinky and the hand. It was in a cast for two weeks and then I was told not to do anything for another two. After the month my hand was fine however I re broke it a couple months later and the same procedure was done. For some reason though after this cast was taken off I was unable to straighten my finger but at first I thought it was just stiff.
Considering it's been almost two years and I still can't straighten my finger and if someone forces it to straighten it hurts is rather worrying. The knuckle also gets very sore when cold.
Help would be much appreciated.