TRIGGER FINGER
Thickening of either A1 Pulley and/or
Nodule in superficial tendon caused by friction against A1 pulley

Initially finger clicks as tendon passes under pulley
Late stages finger locks in flexion
Can effect a finger or the thumb

Most are of unknown cause
Some are secondary to rheumatoid arthritis, gout and diabetes.
Repeated and strong gripping said to predispose

IMAGING
US good at demonstrating the pulley or finger fibroma
If the fibroma is in the finger it usually affects the superficial tendon
Prior to the phase of true triggering, the A1 pulley may be seen to be elevated by the stiffened tendon

The dynamic aspect of US can also be used to guide sheath injection
and guide percutaneous division of a pulley fibroma if one is present