THE LOWER LIMB 541 



lower part of the patellar surface of the femur. In extreme flexion, as in the 

 position assumed by the miner when at work, the patella is entirely off the 

 patellar surface of the femur, and, being turned outwards by the internal 

 condyle, the inner vertical facet of the patella articulates with the semilunar 

 facet on the outer part of the tibial surface of the internal condyle close to the 

 intercondylar fossa, and the upper and outer horizontal patellar facet is in 

 contact with the front part of the external condyle of the femur. When the 

 patella is turned inwards in extension of the joint, the outer lateral patellar 

 hgament is put upon the stretch, and so prevents over-displacement inwEirds. 

 When the patella is turned outwards in flexion by the internal condyle, the 

 inner lateral patellar hgament is put upon the stretch, and so prevents over- 

 displacement outwards. 



When a person stands erect with both feet upon the ground, the vertical 

 line of the centre of gravity faUs in front of the axis of movement at the 

 knee-joint. There is thus a tendency to over-extension, which, however, is 

 resisted by the tension of the Ugaments. In the erect attitude the knee-joint 

 is, therefore, mjiintained in a state of extension to a large extent without 

 muscular effort. This is proved by the fact that each patella is freely 

 movable. When, however, one Umb is raised from the ground, muscular 

 effort now becomes necessary to maintain extension, and the patella of 

 each hmb becomes fixed. The gluteus maximus and tensor fasciae femoris 

 muscles, acting through the iho- tibial band of the fascia lata, contribute to 

 the maintenance of extension at the knee-joint, as in standing. 



Bursae at Knee-Joint. — The region of the knee-joint abounds in 

 bursae, and in this respect surpasses other articular regions. The 

 bursae are as follows: 



Suprapatellar. Popliteal. 



Subcrureal. Of popliteal tendon. 



Prepatellar. Of semimembranosus tendon. 



Infrapatellar. Gastrocnemiai, mesial. 



Anserine. Gastrocnemiai, lateral. 



Bicipital. 



The suprapatellar bursa is a large pouch of the synovial mem- 

 brane of the knee-joint, which extends upwards upon the front of 

 the shaft of the femur for about 2 inches above the upper border 

 of the patellar articular surface of the bone. It lies beneath the 

 suprapatellar tendon of the quadriceps extensor muscle, and its 

 cavity is necessarily continuous with that of the sjTiovial membrane 

 of the knee-joint. In cases of extensive effusion into that joint 

 this bursa becomes distended with fluid, and forms a large swelling, 

 which readily admits of palpation. Superiorly it usually com- 

 municates with the subcrureal bursa. 



The subcrureal bursa hes upon the front of the femur above, or 

 higher up than, the suprapatellar bursa. It is situated beneath the 

 subcrureus muscle, and usually communicates with the suprapatellar 

 bursa, of which it may be regarded as a differentiated part. 



The prepatellar bursae are situated in front of the patella. There 

 may be three of these — namely, subcutaneous, subfascial, and sub- 

 tendinous — or there may only be one — namely, subcutaneous. 



The subcutaneous prepatellar bursa is situated beneath the integu- 

 ment, in front of the lower part of the pateUa and upper part of 

 the hgamentum patellae. It may be more or less multilocular, and 

 it is the seat of the condition known as housemaid's knee. This 

 bursa is always present. 



