Most of the time, it comes from a repeated motion or forceful use within your finger or thumb. Tendons are fibrous cords that attach muscle to bone. Each and every tendon is surrounded by a protective sheath.  Scleroderma: This could cause calcifications from the skin and all-around joints, joint contractures, https://www.theorthopaedicandpainpractice.com/why-cant-i-straighten-the-tip-of-my-finger/