The histopathology of the central parts of 40 A1 pulleys from adult patients with primary trigger fingers was studied using light and electron microscopy and the findings were compared with those in a control series of 10 normal A1 pulleys. The normal A1 pulley revealed a bi-laminar structure: the deepest layer was composed of dense connective tissue and the outermost layer was formed by loose connective tissue. In trigger digits, the A1 pulley had a tri-laminar structure: the deepest layer was composed of irregular connective tissue with chondroid metapalsia, and the middle and outer layers were similar to the normal A1 pulley.
The findings from this study suggest that only the inner portion of the A1 pulley changes in trigger digits. The authors postulate that the changes may be related to an increase of pressure in the A1 pulley as a result of abnormal frictional forces developed during digital flexion. These forces could precipitate differentiation of fibrocytes located in the inner portion of the pulley towards condroid-metaplasia.
Trigger, Finger, Pathology, Metaplasia, Tenosynovits