THE TIBIO-FIBULAK JOINTS. 349 



The anterior margin of the intercondyloid fossa is also brought into contact with the front of 

 the anterior cruciate ligament. 



In the position of extension the patella is retained at such a proximal level in relation to the 

 trochlear surface of the femur, that the distal articular facets of the patella are in contact with 

 the trochlea. 



During locomotion the movements of the knee-joint are somewhat intricate, for both the 

 femoro-tibial and the femoro-patellar sections of the joint are brought into action. The principal 

 movement which results is flexion, with which there is associated, both at its beginning and 

 ending, a certain amount of screw movement or rotation. Flexion and rotation occur at the 

 femoro-tibial sections of the joint, whereas the movement at the femoro-patellar portion produces 

 a regulating and controlling influence upon flexion. 



Taking these factors separately, we observe that each femoral condyle adapts itself to a 

 shallow cup formed by the corresponding tibial condyle and meniscus, and as the two femoral 

 condyles move simultaneously and parallel to each other, there is more than the characteristic 

 hinge-joint action, for each femoral condyle glides and rolls in its cup " like a wheel restrained 

 by a drag" (Goodsir) when the movement of bending occurs. Thus the different parts of 

 the condyles are successively brought into relation with the transverse axis of the joint while it 

 passes from extension to flexion and vice versa. From the fact that the medial femoral condyle 

 is longer than the lateral, it is believed that extension is completed by a movement of rotation 

 whereby the joint becomes locked, and the anterior cruciate, the posterior and the collateral 

 ligaments, become tense. A similar rotation initiates the movement of flexion, and unlocks the 

 joint by relaxing the ligaments just mentioned. 



Since the tibia and foot are fixed in the act of walking, it is the femur which rotates upon 

 the tibia in passing from extension to flexion and vice versa ; and as relaxation of the ilio-femoral 

 ligament is essential for this rotation, some observers are of opinion that the body weight falls 

 behind the transverse axis of the knee-joint, as in the case of the hip-joint, and consequently that 

 extension of the knee-joint is maintained by the ilio-femoral ligament, as it is not possible to 

 bend the knee without first having bent the hip -joint. 



During flexion and extension the menisci glide along with the condyles, so as to maintain 

 their close adaptation and preserve their value as packing agents. When the movement of flexion 

 is completed, the condyles are retained upon the tibia, and prevented from slipping off by the 

 tension of the posterior cruciate ligament. In this position a small degree of rotation of the 

 tibia, both medially and laterally, is also permissible. 



The regulating and controlling influence of the femoro-patellar portion of the articulation is 

 brought into play during the movements of flexion and extension. In the latter position the 

 distal pair of patellar facets is in apposition with the proximal part of the femoral trochlea. As 

 flexion advances, the middle pair of facets adapt themselves to a deeper area of the trochlea, into 

 which the patellar keel fits. When flexion is still further advanced, the proximal pair of patellar 

 facets will be found fitting into that part of the trochlea adjoining the intercondyloid notch ; 

 and finally, when flexion is complete, the patella lies opposite the intercondyloid notch, while 

 the forward thrust of the longer medial femoral condyle brings its semilunar facet (Goodsir) into 

 apposition with the somewhat vertical facet at the medial border of the patella. The wedge-like 

 influence of the patella is most marked, for it is only in the position of extension that it can be 

 moved from side to side. The movements of the patella may be described as gliding and 

 co-aptation, as it slips or rocks from one pair of facets to another in its progress along the trough 

 of the femoral trochlea. 



ARTICULATIONES TIBIOFIBULARES. 



The Tibio-Fibular Joints. The proximal and distal ends of the fibula articulate 

 with the tibia. Primarily, the fibula is required to form a strong lateral support 

 for the ankle-joint, and therefore its articulations are so arranged as to provide 

 a certain amount of elasticity without any sacrifice of the rigidity necessary 

 for security. Hence the amount of movement is very small, but what there is 

 enables these joints to be classified as arthrodial diarthroses. 



Articulatio Tibiofibularis. The proximal tibio-fibular joint is formed, on the 

 one hand, by a flat oval or circular facet which is situated upon the postero-lateral 

 aspect of the lateral condyle of the tibia, and is directed distally and posteriorly ; 

 on the other hand, by a similar facet on the proximal surface of the head of the 

 fibula in front of the apex capituli. 



An articular capsule (Fig. 317) invests the joint, and it may be regarded 

 as holding the articular surfaces in apposition, although certain special bands 

 receive separate designations. Occasionally there is an opening in the stratum 

 fibrosum by which communication is established between the articular cavity and 

 the knee-joint, through the intermediation of the synovial prolongation, subjacent 

 to the tendon of the popliteus muscle. 



The proximal epiphyseal line of the fibula is extra-capsular. 



