Embryonic and fetal development of the human knee with an emphasis on the posterior cruciate ligament: a literature review

An understanding of the embryonic and fetal formation of the knee can help elucidate the relationships between the various structures and clinical conditions. While there have been studies published on the steps of knee development by sectioning human embryos and fetuses, the goal of this review is to consolidate these findings and images into one cohesive work. The timing and appearance of the structures in the knee are outlined with a focus on the cruciate and meniscofemoral ligaments (MFLs). In particular, the posterior cruciate ligament is emphasized with its relationship to other intraarticular structures and congenital anomalies that may arise. The steps of embryological development are outlined by the 23 stages of Carnegie embryonic staging system, which are distinguished by morphological criteria seen on histology of embryo sections. These images highlight the mesenchymal tissue within the interzone of the knee that form the primitive cruciate ligaments and menisci and the subsequent development of the cavitations within the knee that start to give it an appearance similar to that of an adult knee. The steps of fetal development are outlined by the weeks of development with the histological images showing the development of articulations between structures. This review paper consolidates various sources throughout the literature to outline the embryological and fetal appearance and relationship of intraarticular structures in the knee, such as the cruciate and MFLs, and how their altered development may contribute to the congenital anomalies and clinical conditions that may arise.