Most of the time, it comes from a recurring motion or forceful use within your finger or thumb. Tendons are fibrous cords that connect muscle mass to bone. Each individual tendon is surrounded by a protecting sheath.  Scleroderma: This may cause calcifications inside the skin and about joints, joint contractures, https://www.theorthopaedicandpainpractice.com/why-cant-i-straighten-the-tip-of-my-finger/