Duptruytren's contracture of the hand is a knotty and stringy increase of the palmar aponeurosis (planar, subcutaneous connective tissue plate of the palm that locally protects nerves and tendons) through so called myofibroblasts (connective tissue cells).
This proliferation of collagen is also called fibromatosis and is seen as benign. Depending on the extent of the changes, tedon shortening can cause extension deficits of the fingers that are functionally a flexion contracture (in the case shown there is no impaired funtion).
(whole hand)