540 A MANUAL OF ANATOMY 



mencement of flexion, the femur is rotated outwards on the tibia. When 

 the joint is completely extended, the following ligaments are rendered tense : 

 (i) anterior crucial, (2) posterior ligament, and (3) long external lateral and 

 internal lateral ligaments. Over-extension is checked (i)by the tightening 

 of the anterior crucial, the posterior ligament, and the two lateral ligaments ; 

 (2) by the anterior portions of the semilunar fibro-cartilages being pressed 

 into the depressions of the femoral condyles ; (3) by the locking which takes 

 place between the anterior crucial ligament and the front part of the inter- 

 condylar fossa ; and (4) by the locking which takes place between the inner 

 depression of the outer femoral condyle and the front of the outer tubercle 

 of the tibial spine (Bruce Young). At the end of extension the outer con- 

 dyle pushes the anterior and inner part of the external semilunar fibro-cartilage 

 over the anterior and inner border of the outer condylar surface of the 

 tibia. When this has been done, the depression at the inner end of the 

 groove on the outer condyle comes into contact with the front of the outer 

 tubercle of the tibial spine, and with a special facet in front of that tubercle 

 (at the anterior and inner part of the outer condylar surface of the tibia), 

 and so the locking takes place. 



In flexion of the knee-joint the external ligaments are relaxed, except 

 the ligamentum patellae. Over-flexion is checked by (i) the stretching of 

 the quadriceps extensor cruris ; (2) the meeting of the fleshy parts of the 

 calf and back of the thigh ; (3) the tightening of the posterior crucial 

 ligament ; and (4) the extreme posterior and outer part of the inner condyle 

 (which here presents a special facet) being pressed against the back part 

 of the inner tubercle of the tibial spine (Cleland). 



In extension of the joint the semilunar fibro-cartilages move forwards, 

 and in flexion they move backwards. 



Rotation. — This movement is impossible in extension of the knee-joint, 

 owing to the tightening of the anterior crucial and the external ligaments, except 

 the ligamentum patellae. In semiflexion, however, a fair amount of rotation 

 is allowed. Internal rotation is checked by the anterior crucial ligament, 

 and external rotation by the internal lateral ligament. 



The range of rotation is about 40 degrees. Assuming that all the muscles 

 and external ligaments are cut, in which case the femur and tibia would be 

 connected only by the crucial ligaments, if the femur is grasped firmly and 

 the tibia rotated inwards the movement will be seen to be arrested by the 

 tightening of the anterior crucial ligament. If, however, the tibia is rotated 

 outwards neither crucial ligament interferes with the movement, so that the 

 tibia can be made to describe half a circle, thus directing the front of the 

 head of the bone backwards. 



Muscles concerned in the Movements — Flexion. — The muscles which pro- 

 duce flexion are the biceps femoris, semitendinosus, semimembranosus, sar- 

 torius, gracilis, and popliteus. If the ankle-joint is fixed, the gastrocnemius, 

 with the plantaris as a feeble auxiliary, acts as a flexor. Extension. — 

 The chief extensor is the quadriceps extensor cruris. The gluteus maximus 

 and tensor fasciae femoris, however, take part in the completion of extension 

 by means of the ilio-tibial band of the fascia lata. Internal Rotation. — This 

 movement is produced by the popliteus, semitendinosus, semimembranosus, 

 gracilis, and sartorius, in each case after flexion has been effected. External 

 Rotation. — This movement is produced by the biceps femoris after it has 

 flexed the joint. 



Femoro - patellar Joint. — The movement at this joint is of a gliding 

 or to-and-fro nature, associated with a certain amount of rolling of the patella, 

 the result of which is to bring different parts of the opposed articular surfaces 

 into contact in different positions of the joint. This combination of gliding 

 and rolling constitutes the movement called coaptation. In extension of the 

 knee, when the patella is drawn up by the quadriceps extensor cruris, the 

 inferior pair of patellar facets are in contact with the upper part of the patellar 

 surface of the femur. In semiflexion the middle pair of patellar facets are 

 in contact with the middle part of the patellar surface of the femur. In 

 ordinary flexion the upper pair of patellar facets are in contact with the 



