Blood and lymph supply of the posterior cruciate ligament: a cadaver study

Injection techniques, immunohistochemical (antibodies against laminin), and histochemical (5'-nucleotidase activity) methods were employed to describe the vascular pattern of the human posterior cruciate ligament (PCL); in parallel we used conventional light microscopy and immunohistochemical techniques to visualize the histological structure of the PCL. The blood supply of the PCL mainly arises from the middle geniculate artery. The ligament is covered by a synovial fold where the terminal branches of the middle geniculate artery form a periligamentous network. From the synovial sheath, the blood vessels penetrate the ligament in a horizontal direction and anastomose with a longitudinally orientated intraligamentous network. Within the ligament the blood vessels are located in the loose connective tissue that is sited between longitudinal fibre bundles. Histologically the longitudinal fibre bundles of the ligament consist of dense connective tissue. Lymphatics accompany most of the smaller blood vessels, showing similar regional distribution. Compared to the surrounding synovial layer, the amount of vessels in the substance of the ligament is lower. The distribution of blood vessels within the PCL is not homogenous: we detected three avascular areas within the ligament. Both fibrocartilaginous entheses of the PCL are devoid of blood vessels, and a third avascular zone is located in the central part of the middle third. The histological structure of this zone varies from the rest of the PCL which consists of the characteristic dense connective tissue. In the central part of the PCL the tissue resembles fibrocartilage: the cell shape is round, the pericellular matrix of those cells is rich in acid glycosaminoglycans and the immunohistochemical demonstration of type II collagen is positive. The occurrence of an avascular zone within the central part of the middle third of the PCL where the tissue consists of fibrocartilage has not been described in the literature.