172 ARTICULATIONS OF THE LO^YER LIMB, 



the femoral sm-face ; and in extreme flexion the patella, which has been 

 gradually turned outwards by the increasing prominence of the inner condyle, 

 rests by its innermost facet on the outer margin of that condyle. Tlie articula- 

 tion between each condyle and the opposed almost liat surface of the tibia, while 

 resembling, is not exactly a hmge joint, and extension and flexion, the move- 

 ments of which it is capable, are produced by a combination of gliding, rolling, 

 and rotation. If the condyles of the femur be examined as they rest upon the 

 tibia in the flexed position of the joint, it will be seen that the inner condyle is 

 longer than the outer, and that its anterior portion inclines obliquely outwards, 

 to reach the patellar surface. In the movement of extension the condjdes move 

 parallel to one another, both gliding and rolling- until extension is nearly com- 

 pleted, and then, the anterior part of the rolling surface of the external condyle 

 having- already come into contact with the tibia, the inner condyle continues to 

 glide backwards, liringing its oblique anterior part into contact with the tibia, so 

 that the bone is rotated inwards on the tibia, and over-extension is iDrevented, 

 not merely by the tightness of the ligaments, but by the femur being pressed up 

 against the tibial spine. In complete extension the lateral ligaments and the 

 external crucial ligament are tight, while the i:io.sterior crucial ligament is 

 relaxed : in flexion, the posterior crucial ligament only is tightened, the others 

 being relaxed. In extension of the joint no rotation of the leg is possible ; in 

 the flexed condition a considerable amount is allowed. The semilunar cartilages 

 being loosely attached to the head of the tibia, move forwards in extension and 

 backwards in flexion of the jomt : and further, as the condyles rolling upon the 

 til)ia present to the condylar surfaces of that bone portions having diflferent 

 curvatures, each cartilage, like a moveable wedge, is contracted round the con- 

 kV-^i^. . dyle during flexion of the joint and I ' olajiotL during extension. In extension of 

 the knee, as the weight of the Iwdy keeps the bones in then- position, the extensor 

 muscles are relaxed, the patella di-ojis down from its position in contact with the 

 femur, and the ligamentum mucosum then comes into plaj', supporting the 

 sjmovial membrane and fat below the patella. As the line of the centre of 

 gravity of the body in the erect attitude descends in front of the axis of motion 

 of the knee-joint, there is a tendency to over extension or the joint, which is 

 resisted by the tension of the two lateral and the iiosterior ligaments, as well as 

 of the anterior crucial, and thus the mamtenance of the erect attitude without 

 musculixr efi^ort is partly due to the mechanism of the knee-joint. (See Meyer, 

 op. cit. ; Goodsir, " Anatomical Memoirs,"' vol. ii. jip. 220. 2)51 ; Langer, " Sitz- 

 ungsber d. Acad, der Wissensch. Wien," 1858 ; Henke, '' Zeitschr. fiii- rat. Med.,"' 

 V. viii., ISy'J.) 



TIBIO-FIBTJLAB ARTICULATIONS. 



The tibia and fibula are connected at their upper and lower extremities 

 by synovial articulations, and their shafts are united by an interosseous 

 membrane. 



Upper tibio-fibular arfcictilation. — The su})erior extremities of the 

 bones present two flat oval articular surfaces, retained in close contact 

 by an anterior and a posterior superior iihio-JUnitar ligamnit, both of 

 which pass u^nvards and inwards from the head of the fibula to the 

 external tuberosity of the tibia. The synovial membrane which lines 

 this joint not unfrequently communicates posteriorly with that of the 

 knee. 



The interosseous membrane or ligament, which connects the 

 shafts of the tibia and fibula, passes between the external ridge of the 

 tibia and the ridp^e on the inner surface of the fibula, and is composed 

 for the most part of parallel fibres running outwards and downwards, 

 only a few fibres crossing them in a difiFerent direction. The membrane 

 is broader above than below, and presents superiorly an elongated 

 opening for the transmission of the anterior tibial vessels, and iuferiorly 



