Background: The embryology of the cruciate ligaments of the knee had received scant attention in the orthopaedic and embryologic literature. Understanding the embryonic development of the blood supply to criciate ligaments (CL) may help to comprehend the mechanisms of pathology leading to failure of these structures and of the revascularization process after reconstruction injured of cruciate ligaments or implantation of grafts.

Aim: To describe the anatomy and spatial relationships of the cruciate ligaments and their blood supply in the developing fetus.

Method: Knees from one leg of 48 normal human embryos from abortion material were examined, gestational age varying from early as the 8^th week and up to the 20^th week. Microscopic semi serial consequent sections of the knees were examined under light microscope and spatial changes within the cruciate ligaments were noted. The contra-lateral knees of some of the embryos were dissected to confirm the three dimensional picture. This gave us the possibility to follow the developmental changes of the spatial orientation of the cruciate ligaments and the blood vessels within them.

Results: The anterior and posterior cruciate ligaments are formed from a single mass of cells, divided by a sinovial septum. Folds within the septum partially divide the ligaments into bundles and carry within them the vasculature needed to sustain the ligaments. We show that the blood supply of the growing CL arises from the middle genicular artery and enters the ligaments from the poster-superiolateral corner (P.S.L.C.) of the inter-condylar notch, passes between the ACL and PCL and descends along he posterior aspect of the ACL.

These findings can explain why injury involving the P.S.L.C. in the adult has a worse prognosis for rehabilitation.