THE KNEE-JOINT 337 



external lateral ligament between it and the tendon of the Popliteus (this is sometimes only an 

 expansion from the next bursa); (4) one beneath the tendon of the Popliteus (bursa musculi 

 poplitei) between it and the condyle of the femur, which is almost always an extension from the 

 synovial membrane of the joint. On the inner side there are five bursae: (1) One beneath the 

 inner head of the Gastrocnemius, which sends a prolongation between the tendons of the Gastroc- 

 nemius and Semimembranosus; this bursa often communicates with the joint; (2) one above 

 the internal lateral ligament between it and the tendons of the Sartorius, Gracilis, and Semi- 

 tendinosus; (3) one beneath the internal lateral ligament between it and the tendon of the 

 Semimembranosus; this is sometimes only an expansion from the next bursa; (4) one beneath 

 the tendon of the Semimembranosus, between it and the head of the tibia; (5) sometimes there 

 is a bursa between the tendons of the Semimembranosus and of the Semitendinosus. 



Structures around the Joint. In front and at the sides, the Quadriceps extensor; on the 

 outer side, the tendons of the Biceps femoris and the Popliteus and the external popliteal nerve; 

 on the inner side, the Sartorius, Gracilis, Semitendinosus, and Semimembranosus; behind, an 

 expansion from the tendon of the Semimembranosus, the popliteal vessels, and the internal 

 popliteal nerve, the Popliteus, the Plantaris, and the inner and outer heads of the Gastrocnemius, 

 some lymph nodes, and fat. 



The arteries supplying the joint are derived from the anastomotica magna branch of the 

 femoral, articular branches of the popliteal, anterior and posterior recurrent branches of the 

 anterior tibial, and a descending branch from the external circumflex of the profunda. 



The nerves are derived from the obturator, femoral, and external and internal popliteal. 



Movements. The knee-joint permits of movements oi flexion and extension, and, in certain 

 positions, of slight rotation inward and outward. The movement of flexion and extension does 

 not, however, take place in a simple, finger-like manner, as in other joints, but is a complicated 

 movement, consisting of a certain amount of gliding and rotation; so that the same part of one 

 articular surface is not always applied to the same part of the other articular surface, and the 

 axis of motion is not a fixed one. If the joint is examined while in a condition of extreme flexion, 

 the posterior part of the articular surfaces of the tibia will be found to be in contact with the 

 posterior rounded extremities of the condyles of the femur; and if a simple hinge-like movement 

 were to take place, the axis, around which the revolving movement of the tibia occurs, would be 

 in the back part of the condyle. If the leg is now brought forward into a position of semiflexion, 

 the upper surface of the tibia will be seen to glide over the condyles of the femur, so that the 

 middle part of the articular facets are in contact, and the axis of 

 rotation must therefore have shifted forward" to nearer the centre 

 of the condyles. If the leg is now brought into the extended posi- 

 tion, a still further gliding takes place and a further shifting for- 

 ward of the axis of rotation. This is not, however, a simple 

 movement, but is accompanied by a certain amount of rotation 

 outward around a vertical axis drawn through the centre of the 

 head of the tibia. This rotation is due to the greater length of 

 the internal condyle, and to the fact that the anterior portion 

 of its articular surface is inclined obliquely outward. In conse- 

 quence of this it will be seen that toward the close of the move- 

 ment of extension that is to say, just before complete extension 

 is effected the tibia glides obliquely upward and outward over tw g- JgtoJdP & *&& 

 this oblique surface on the inner condyle, and the leg is therefore showing diagrammatical!} the 

 necessarily rotated outward. In flexion of the joint the converse fn^dl^rent^posSs^^f^'the 

 of these movements takes place; the tibia glides backward around knee, 

 the end of the femur, and at the commencement of the move- 

 ment the tibia is directed downward and inward along the oblique curve of the inner condyle, 

 thus causing an inward rotation to the leg. 



During flexion a- id extension the patella moves on the lower end of the femur, but this- 

 movement is not a umple gliding one; for if the articular surface of this bone is examined, it 

 will be found to present on each side of the central vertical ridge two less marked transverse 

 ridges, which divide the surface, except a small portion along the inner border, which is cut off 

 by a slight vertical ridge into six facets (Fig. 272), and therefore does not present a uniform 

 curved surface as would be the case if a simple gliding movement took place. These six facets 

 three on each side of the median vertical ridge correspond to and denote the parts of the bone, 

 respectively, in contact with the condyles of the femur during flexion, semiflexion, and extension. 

 In flexion only the upper facets on the patella are in contact with the trochlea of the femur; the 

 lower two-thirds of the bone rests upon the mass of fat which occupies the space between the 

 femur and tibia. In the semiflexed position of the joint the middle facets on the patella rest 

 upon the most prominent portion of the trochlea, and thus afford greater leverage to the Quad- 

 riceps by increasing its distance from the centre of motion. In complete extension the patella 

 is drawn up, so that only the lower facets are in contact with the trochlea. The narrow strip 



22 



