👉 Condylarthrosis is a condition that occurs when the joint between the metacarpophalangeal (MPP) and proximal phalanx joints of the thumb is affected. The MPP is a ligamentous structure that connects the two bones in the hand, while the proximal phalanx is a bone that supports the thumb. When this joint becomes inflamed or damaged, it can cause pain, swelling, and reduced function in the thumb.