chapter 1: normal anatomy
Vascular Anatomy of the Patellofemoral Joint
The patellofemoral joint enjoys a rich vascular anastomosis, receiving arterial input from the medial and lateral sides both superiorly and inferiorly (Fig. 1.18). Superiorly, the lateral superior genicular artery passes through the insertion of the lateral intermuscular septum and sends a branch to the superolateral border of the patella. This branch anastomoses anteriorly and through the quadriceps insertion with branches of the medial superior genicular artery approaching the superomedial aspect of the patella. Distally, the medial inferior genicular artery approaches the patella and sends anastomosing branches both superiorly, paralleling the medial border of the patella, and laterally, behind the patellar tendon, to anastomose with the lateral inferior genicular artery. The anterior tibial recurrent artery also approaches the inferolateral border of the patella. In fact, the fat pad is an important source of blood supply entry into the patella (34). The six named arterial components of the patellar circulation anastomose freely around the patella forming a peripatellar circle.
Outside of this anastomotic peripatellar system, which richly supplies the anterior or patellar portion of the patellofemoral joint, there also exist two other deep anastomotic systems coming from the same superior and inferior genicular arteries that form the blood supply to the femur and tibia underneath the synovial coverings. These two arcades then irrigate the synovium and epiphyses of the tibia and femur. It is evident, then, that the patellofemoral joint is supplied on its two sides by six peripheral vascular sources from the same origin, which anastomose on two levels—one superficial and the other deep. This anatomical distribution of arterial blood supply demonstrates a remarkable vascular unity, particularly with regard to the patella, which receives branches from all directions, with the peripatellar circle providing entry into the patella itself through two principal routes: one through the middle third of the anterior surface and the other at the level of the inferior extra articular portion of the posterior surface (35).
Transpatellar venography has been carried out in a series of patients by injection of contrast medium directly into the cancellous bone of the patella, demonstrating the distribution of the venous drainage of the patella. This phlebography reproduces the general vascular peripatellar framework that has just been described on the arterial side and permits several comments. The richness of the venous elements of small caliber sometimes hinders interpretation of the phlebograms and the identification of the principal drainage pathways. The inferior pole of the patella appears to be the veritable vascular hilus of this bone (Fig. 1.19, A and B). The vascular penetration of the anterior surface seems to be much more the accessory system. The two principal drainage routes consist of, in the first instance, the popliteal vein, the midportion of which is usually well visualized, and second, the internal saphenous vein. One discovers, in general, the same kind of picture as the arterial input, but the anterior recurrent tibial veins are not always visualized. When carrying out phlebography, one should always observe the medullary circulation by taking a radiographic film 15 minutes after the injection of opaque material, by which time all material should have cleared the bone unless intraosseous stasis exists. Thus, the patella is not a bone that is poorly vascularized as some have written, but, on the contrary, is well nourished and well drained by multiple ports of entry, both anteriorly and posteriorly, and supplemented by a rich anastomotic system.
The intramedullary pressure that prevails is similar to that which has been found at other points in the body, and averages between 10 and 15 mm Hg. The bone blood flow is controlled by various systemic and local factors that influence bone blood flow in general, particularly the sympathetic system. This vascular system both determines and is influenced by joint function. Much as the architectural anatomy of the bone structures is modeled according to the functional constraint of the joint itself, so the vascular anatomy is also influenced by joint function. The vascular anatomy demonstrates the relative independence of the patellofemoral joint in that it possesses its own true vascular tree. However, there is some interdependence with the femorotibial articulation because the deep anastomotic branches also participate in nutrition of the femoral and tibial epiphyses, anastomosing with the posterior network as well. Pathologic conditions of the vascular system can affect the entire knee or simply one of its components, such as the patellofemoral compartment.
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