M66.3: Spontaneous rupture of flexor tendons

Spontaneous rupture of flexor tendons, denoted by the ICD-10 code M66.3, refers to a medical condition where the flexor tendons - the tough, fibrous tissues that connect the muscles of the hand to the bones - suddenly break or tear. The condition is called 'spontaneous' because it typically occurs without any apparent injury or undue stress on the tendon. Pain, stiffness, loss of function, and a sensation of a pop or snap in the hand or finger are common signs of this condition. Bending or flexing the fingers might become difficult or impossible. A notable characteristic of the condition is that it often affects individuals with predisposing factors, such as rheumatoid arthritis or systemic lupus erythematosus, which can cause weakening of the tendons. If left untreated, spontaneous rupture of the flexor tendons can result in permanent loss of finger mobility.