158 ARTICULATIONS OF THE LOWER LIMB. 



femur, the inferior limits of the patellar surface are quite distinguishable ; the line 

 which separates this surface from the outer tibial joint passing directly between it 

 and the condyle, and that which separates it from the inner joint being continued 

 backwards, so as to cut off from the rest of the inner condyle a narrow tract at the 

 side of the intercondyloid fossa. 



The movement of the patella on the femur is one partly of gliding, partly of 

 coaptation. This is illustrated by a careful examination of the articular surface of 

 the patella, which is not uniformly curved from above downwards, as it would be, 

 were the movement one of gliding only, but exhibits on each side of the vertical ridge 

 three very slightly depressed surfaces, separated by two slight transverse elevations, 

 and along the inner margin a seventh area, upon which the transverse lines do not 

 encroach (Goodsir). When the knee is extended, and the patella drawn upwards by 

 the extensor muscles, the two inferior facets of the patella are in contact with the 

 upper margin of the femoral surface ; in semiflexion the middle facets only are in 

 contact with the femur; in greater flexion, the superior parts of the patella are 

 in contact with the lower part of the femoral surface; 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 intercondyloid margin of that 

 condyle. 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 more elongated 

 than the outer, and that the portion of the inner condyle which lies in front of the 

 anterior limit of the external condyle inclines obliquely outwards, to reach the patellar 

 surface. In the movement of extension the condyles move parallel to one another, 

 until complete extension is nearly reached, 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, and brings its oblique anterior part 

 into contact with the tibia, so that the bone is rotated inwards on the tibia, and 

 over-extension is prevented, 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 posterior crucial 

 ligament is relaxed; in flexion the external and internal lateral and the external crucial 

 ligaments become relaxed, and the posterior crucial ligament is tightened. In exten- 

 sion of the joint no rotation of the leg is possible ; in the flexed condition a consider- 

 able amount is allowed. When the weight of the body keeps the bones in their position 

 in the extended knee, the extensor muscles are relaxed, the patella drops down from 

 its position in contact with the femur, and the ligamentum mucosum then comes into 

 play, supporting the synovial membrane and fat below the patella. (See Meyer, op. 

 cit. ; Goodsir, in " Edin. Med. Journ.," 1855, and" Proceedings of Roy. Soc. of Edin." 

 1858; Langer, " Sitzungsber. d. Acad. der Wissensch. Wien,"1858; Henke, "Zeitschr. 

 fUr rat. Med.," v. viii., 1859.) 



ARTICULATIONS OF THE LEG AND ANKLE. 



PERONEO-TIBIAL ARTICULATIONS. The tibia and fibula are connected at 

 their tipper and lower extremities by synovial articulation, and their shafts 

 are united by an interosseous membrane. 



The superior extremities of the bones present two flat oval articular surfaces, 

 retained in close contact by an anterior and a posterior superior tibio-fibular 

 ligament, both of which pass upwards 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 

 ridge 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 different direction. The membrane is broader above tban below, 

 and presents superiorly an elongated opening for the transmission of the 

 anterior tibial vessels, and inferiorly a small aperture for the passage of the 

 anterior branches of the peroneal vessels. 



