More often than not, it comes from a recurring movement or forceful use of the finger or thumb. Tendons are fibrous cords that attach muscle mass to bone. Just about every tendon is surrounded by a protective sheath.  Numbness and Tingling: A typical symptom in disorders like Carpal Tunnel Syndrome, https://www.theorthopaedicandpainpractice.com/why-cant-i-straighten-the-tip-of-my-finger/