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

Objectives Digital annular pulleys (DAPs) are important anatomical structures for finger function. The anatomy, histology and imaging assessment of DAPs, particularly at the level of their entheses, are still not clearly defined. The advent of high-frequency US transducers opened new perspectives in evaluating submillimetre-scale structures, such as pulleys, paving the way for their global assessment. The study aimed to characterize DAPs 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. DAPs in 20 healthy controls (HCs) were detected and measured by US. The A1, A2 and A4 DAP entheses were assessed using a new dynamic manoeuvre to better evaluate those structures.Results A total of 1200 DAPs (400 cadaveric, 800 HCs) were analysed. The cadaveric study demonstrated strong correlation between anatomical and US measurement of DAPs (r = 0.96). At the histological level, DAP entheses at the volar plate, sesamoid bones or phalangeal ridges contained fibrous and fibrocartilaginous tissue. US assessment of A1, A2 and A4 DAPs in HCs allowed the identification of 718/720 (99.73%) entheses.Conclusion US is an effective tool to detect and study DAPs. DAP entheses reveal both fibrous and fibrocartilaginous characteristics. A newly described manoeuvre to optimize DAP enthesis visualization enhances their detection by US.