What triggers in trigger finger? The flexor tendons at the Flexor Digitorum Sublimis bifurcation

Publication date: Available online 27 May 2017
Source:Journal of Plastic, Reconstructive & Aesthetic Surgery
Author(s): X.L. Chuang, C.C. Ooi, S.T. Chin, M.A. Png, S.K. Wong, S.C. Tay, D.A. McGrouther
To define the role of the flexor tendons in trigger finger, a high resolution ultrasound examination was undertaken in 20 trigger fingers and 20 normal contralateral digits in 3 digital postures: full extension, mid flexion and near-full flexion. Precise measurements of diameter and cross sectional area of the combined tendon mass were recorded at 5 clearly defined locations: summit of metacarpal head, proximal lip of proximal phalanx (PP), at 1/8, 1⁄4 and 1/2 length of PP. In the normal tendons, there was an anatomical thickening, not previously appreciated at 1⁄4 length PP, in the region of FDS bifurcation. This anatomical region moved proximally on finger flexion to the A1 pulley. In the trigger fingers, the flexor tendons had greater diameter (sagittal view) and cross sectional area than the normal side at all locations (p<0.01, p<0.001), with an even greater increase in diameter in the FDS bifurcation area (p<0.001). Trigger fingers also had thicker A1 pulleys (p<0.001). Triggering occurs on flexing the finger when the enlarged combined flexor tendon mass at the specific anatomical region of the FDS bifurcation impacts on the thickened A1 pulley, resisting its excursion.



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