Why do i have joint stiffness in the middle knuckle of each finger?

See below: Cannot say for sure without a physical exam but osteoarthritis of the fingers typically will affect the middle and end knuckles of the fingers. Rheumatoid arthritis can too but more often it affects the first of the three knuckles of the hands called the mcp joints. Your doctor should be able to figure it out and devise a treatment for you.

Psoriatic Arthritis?: If you are young and have big, sore, or inflammed middle joints of your digits: 2-5, you are more likely to have psoritic arthritis particularly if your large knuckes are not involved. If you are over 50, the DJD of the hands is more likely. If you think you have ra, then have your dr. Get a ccp antibody. It should be positive. If you or a family member has psoriasis, all bets are off on ra!