Arnold Kirkpatrick Henry (1886–1962) and his eponym (Master Knot of Henry): a narrative review

Purpose The aims of this review were to form a more precise description for Master Knot of Henry (MKH), and to modify classifications related to interconnections between flexor hallucis longus (FHL) and flexor digitorum longus (FDL) for showing all configurations in the literature. Methods A literature search was performed in main databases to obtain information related to anatomical definitions and variations of MKH. The search was carried out using the following keywords: “Master Knot of Henry”, “Chiasma plantare”, “Flexor hallucis longus” and “Flexor digitorum longus”. Information extracted from the studies was: sample size, numerical values, classifications, variation types, incidence of types, anatomical definitions of MKH, year of publication, and type of study. Results This study proposes that MKH should be defined as the intersection territory where FDL crosses over FHL in the plantar foot. The postchiasmatic plantar area located at distal to MKH (the narrow space between MKH and the division of FDL) should be termed as the triangle of Henry. Moreover, the classification systems showing different configurations related to interconnections situated at Henry’s triangle were updated as eight types to present all forms in the literature. Conclusion Our definitions may assist in determining the precise anatomical boundaries of MKH, and thus facilitate the use of MKH as a surgical landmark. In addition, our modified classification systems covering all variations in the current literature may be helpful for surgeons and anatomists to understand formations of the triangle of Henry, and the long flexor tendons of the lesser toes.