The Lower Extremity and Pelvis 159 



front and back of the outer tubercle of the spine, the anterior cornu of the inner cartilage 

 is in front by the edge of the inner articular surface, while its posterior cornu is behind 

 the spine also against the edge of the inner surface. The anterior crucial ligament is 

 attached to the tibia behind the anterior cornu of the internal cartilage, but the posterior 

 crucial ligament is on the extreme back part of the intervening non-articular area in the 

 popliteal notch, being really placed on the posterior surface of the bone more than on its 

 upper aspect. 



When these structures are in position the arrangement of ligaments and cartilages 

 on the top of the tibia is as seen in the figure. 



The nbro-cartilages are peripheral rings, deficient centrally, wedge-shaped on 

 section with the base of the wedge applied to the capsular structures : their pro- 

 jection into the cavity divides it into suprachondral and infrachondral parts widely 

 continuous with each other round the thin edge of the wedge. The deeper fibres of 

 the capsule fasten each cartilage (coronary ligaments) to the tibia and femur, but, as 

 those passing to the latter are long and movable and those to the former very short, 

 the menisci move with the tibia * on the femur, gliding forward with it in extension and 

 thus coming to occupy by their front borders the depressions already noticed on 

 the femoral condyles (Fig. 123). 



It is evident that different parts of the menisci come under special pressure during 

 the various ranges of movement of the joint, and that there must, in consequence, be 

 small alterations in shape of these cartilages wedged in between the moving bony 

 surfaces. Attention may be called in particular to the pressure on the external plate 

 exercised by the lower part of the trochlear surface of the femur when the knee is fully 

 extended : the front and inner margin of the cartilage, which already overlaps the edge 

 of the tibial articular surface to some extent, is pressed further over this on to the non- 

 articular part, and a marking may be found on the bone which indicates where this 

 expansion takes place. 



The strength of the knee joint during use depends on the breadth and practically 

 horizontal level of the opposed femoral and tibial surfaces : when standing, for example, 

 the femur rests directly on the tibia and is not supported by the tension of any ligament 

 save, perhaps, that of the Ligamentum patellae, which is, however, tightened to keep 

 the femur upright and not for the purpose of holding it on the tibia. 



But there must be ligamentous bands whose function is to prevent slipping of the 

 bones on one another and also to keep them in proper apposition during movement 

 and to limit this movement. These bands are the two lateral ligaments/ the patellar ^ 

 ligament or tendon, and the crucial ligaments./ The last are mostly concerned in 

 limiting movement and the others in holding the bones in apposition : the capsule fills 

 up the intervals between the lateral ligaments and patellar tendon, and also covers 

 in the posterior aspect of the condylar recesses of the joint. 



The crucial ligaments are attached, as shown in Fig. 131, to the top of the tibia 

 between the articular surfaces : the anterior one passes upwards, backwards, and 

 outwards, to the inner aspect of the outer femoral condyle, the posterior one upwards, 

 forwards, and inwards, to the outer aspect of the inner condyle. The area of attach- 

 ment to the condyles is shown in Fig. 122. 



The sides of the ligaments are covered by the synovial reflections off the condyles 

 between which they lie, and a diverticulum of the trochlear cavity is continued back 

 between them as a sort of bursa (Fig. 122). 



The anterior crucial ligament is evidently made tight by extension of the knee 



* This is. of course, to be expected, since the cornua are attached to the tibia. 



