Varieties.—The popliteal artery very seldom exhibits any deviation from its usual arrange ment ; occasionally, its point of division occurs higher in the popliteal space. Professor Har rison mentions to have seen the artery divide between the condyles of the femur: Instances have been recorded of a high division of the femoral artery (see FEMORAL ARTERY), and where two popliteal arteries existed ; but the artery generally appears particularly free from any variety.
Branches of the popliteal artery.—These are very numerous, and of considerable importance in maintaining a collateral circulation when the femoral artery has been obliterated by operation or disease ; they are not always constant, either in number or size. The popliteal artery first sends some irregular branches to the hamstring muscles, the rami musculares superiores ; then five articular arteries, two of which usually arise a little above the joint, and are called ex ternal and internal superior articular, and two below, the external and internal inferior arti cular ; the last is an azygos branch. After giving off these articular arteries, the popliteal sends several large branches to the gastrocnernii muscles, the rami musculares inferiores.
The superior muscular branches are two or three in number, which are distributed on either side to the hamstring muscles and anastomose with the perforating arteries of the profunda. The superior external articular artery is of some size, and arises from the outer side of the popli teal at a variable distance above the outer con dyle of the femur; it descends to wind round the bone under the biceps muscle,which latter it supplies and divides into superficial and deep branches ; the former are distributed to the vas tus externus muscle, and, by passing through its substance, terminate on the patella ; the lat ter supply the synovial lining of the articulation, and the lower extremity of the femur itself. These branches anastomose with those of the inferior external articular artery, and with the long branches of the external circumflex from the profunda, which descend in the substance of the vastus externus towards the knee.
The superior internal articular artery arises from the inner side of the popliteal above the inner condyle, and also winds round the femur, passing beneath the tendon of the adductor magnus muscle; like the external articular, it divides into superficial and deep branches, the former penetrating the vastus internus to ramify on the patella, and anastomoses with the ex ternal articular and the anastomotica magna from the femoral ; the deeper branch is distri buted to the synovial capsule and femur.
The azygos branch is derived from the ante rior aspect of the popliteal while it is in relation with the posterior ligament of the joint ; it di vides into branches which pass through the liga ment, and supply the synovial membrane and crucial ligaments of the joint. The inferior ex ternal articular is given off from the outer side of the popliteal a little below the articulation, and winds round the outer surface of the ex ternal semilunar cartilage, passing beneath the plantaris and outer head or the gastrocnemius muscles ; it then courses forward above the head of the fibula, and beneath the external lateral ligament to divide into branches, which anastomose with the anterior tibial recurrent and the other articular arteries. The inferior
internal articular artery is generally rather a large branch, and descends to the internal lateral ligament, beneath which it passes to gain the front of the tibia; it divides into numerous branches which are distributed to the structures about the inner side of thejoint, and which anas tomose also with the other articular branches.
These articular branches of the popliteal are seen, when well injected, to form a beautiful network of vessels around the knee-joint; by anastomosing with the external circumflex and perforating branches of the profunda, with the anastomica of the femoral and the recurrent tibial artery, and also with each other, a very sufficient collateral circulation is usually main tained in cases where the femoral artery has been obliterated.* The inferior muscular branches are derived from the popliteal artery while pa.ssing between the heads of the gastrocnemius ; they are four or five in number, and often of considerable size; accompanied by branches from the tibial nerve, they descend in the substance of the gastrocnemii muscles, and may be traced some times to the tendo Achillis ; generally, a small branch from one of them descends with the coinmunicans tibialis nerve. These vessels are sufficiently large as occasionally to require a ligature after amputation of the leg.
The course of the popliteal vein has been already noticed in connection with the artery ; it is remarkable for the thickness of its fibrous coat, and is formed by thejunction of the ante rior tibial veins with a trunk called the tibio peroneal : this latter vessel is produced by the confluence of the posterior tibial and peroneal veins. The popliteal vein receives the veins which accompany the branches of the popliteal artery, and also, about the centre of this re gion, the vena saphena minor.
Operative relations of the popliteal artery. — Operations upon the artery in this region are now never undertaken, unless, perhaps, in cases of injury with an external wound, the 'size and direction of which will vary the surgical treat ment to be adopted ; a ligature may be passed round the artery in the upper part of its course as it emerges from beneath the semimembra nosus muscle, the outer edge of which will act as a guide to the first incision. After dividing the fascia, the finger, sunk into the space and carried upwards upon the outer surface of the semi-membranosus, will reach the artery ; the vein lies behind it, and a little to the outer side, and will therefore be reached first ; the needle must be insinuated between the artery and vein, and carried round the former from without in wards. This operation is mentioned merely as being practicable ; in the rest of its course the relations of the artery are such as to prohibit any surgical operation upon it.
Trew.)