Characterization of digital annular pulleys and their entheses: an ultrasonographic study with anatomical and histological correlations

Abstract

Objectives: Digital annular pulleys (DAP) are important anatomical structures for finger function. The anatomy, histology, and imaging assessment of DAP, particularly at the level of their entheses is still not clearly defined. The advent of high-frequency ultrasound (US) transducers opened new perspectives in evaluating sub-millimeter scale structures, such as pulleys, paving the way for their global assessment. The study aimed at characterizing DAP from an anatomical, histological, and US perspective, focusing on the detection and complete description of pulley entheses. Methods: US assessment and gross anatomy dissection were conducted on 20 cadaveric hands to study DAP thickness and structure including enthesis identification. The results of the US and anatomical measurements were correlated. DAP entheses identified by US were characterized via histological analysis. DAP in 20 healthy controls (HC) were detected and measured by US. The A1, A2, and A4 DAP entheses were assessed using a new dynamic maneuver to better evaluate those structures. Results: 1200 DAP (400 cadaveric, 800 HC) were analyzed. The cadaveric study demonstrated strong correlation between anatomical and US measurement of DAP (r = 0.96). At histological level, DAP entheses at the volar plate, sesamoid bones, or phalangeal ridges contained fibrous and fibrocartilaginous tissue. The US assessment of A1, A2, and A4 DAP in HC allowed the identification of 718/720 (99.73%) entheses. Conclusion: US is an effective tool to detect and study DAP. DAP entheses reveal both fibrous and fibrocartilaginous characteristics. A newly described maneuver to optimize DAP enthesis visualization enhances their detection by US.