Studies of the intratendinous structure of the flexor tendons, and in particular the demonstration of the spiralling of the fibre components within the digits of the flexor tendons of the thumb and fingers, have allowed a new appreciation of the old problem of understanding "trigger finger".The spiral arrangement of the intratendinous fibrous architecture lends itself to the development of a contour defect-or nodule-distal to a stenosed proximal sheath pulley. On release of the constriction the nodule can disappear by aprocess of unspiralling under the normal longitudinal forces acting on the tendon. Whether congenital, traumatic or rheumatoid inflammatory in origin, the relative stenosis of the proximal pulley of the digital tendon theca would appear to be the primary aetiological factor and the triggering only occurs when sufficient deformation of the tendon contour has been induced.