Grasping items and ulnar deviation are the usual mechanisms of injury. Ulnar deviation refers to moving the wrist toward the little finger side of the hand. Sometimes just holding objects for long periods of time can bring this problem on.
Tension from repeated grasping causes thickening and swelling in the area. The area affected is referred to as the first dorsal compartment. Dorsal refers to the back of the hand. The compartment is a tunnel that helps keep the tendons straight and gliding smoothly. There is a sheath or lining inside the compartment that helps protect the tendons. The first compartment is located at the base of the thumb.
The compartment around the tendon swells and enlarges, making thumb and wrist movement painful. Inflammation isn't the main cause of this condition. A degenerative process is really the problem. There's physical wear and tear of the tendons called attrition.
Women are affected six times more often than men, especially in middle age. Pregnancy and nursing babies seems to put younger women at increased risk of de Quervain's. Certain occupations or job tasks are also risk factors. These include factory jobs with repetitive duties, typing, and lifting.