Tendinitis occurs more often as one gets older. However, it is also relatively common in young people who exercise vigorously or perform repetitive physical tasks. Certain tendons are more susceptible to inflammation than others. Tendons in hands and arms are especially at risk. Some tendons are covered by tendon sheaths.
Normal tendons slide easily in and out of the surrounding sheaths.
When a tendon in a finger or thumb becomes inflamed and swollen, it can only straighten by physically forcing the swollen tendon area through the sheath. This forcing causes a popping sound similar to that heard when pulling a trigger. Trigger finger or trigger thumb occurs when the finger or thumb becomes locked in the bent position. This is caused when an inflamed and swollen area of the tendon keeps the tendon from sliding in the sheath. Many forms of treatment are available to alleviate the symptoms of tendinitis.