REGION OF THE KNEE. 539 



The infrapatellar bursts are one between the skin and tibial tubercle and the 

 other between the under surface of the tendo patellae and the upper end of the tibia 

 they are unconnected with the joint and are not often diseased. 



Posteriorly. On the outer side of the joint there may be present (i) a bursa 

 beneath the external head of the gastrocnemius which may communicate with the 

 bursa between the popliteus tendon and external lateral ligament. (2) One be- 

 tween the biceps tendon and external lateral ligament, (3) another between the pop- 

 liteus tendon and external lateral ligament, and (4) one beneath the popliteus, 

 usually an extension of the synovial membrane of the joint. On the inner side : 

 ( I ) one beneath the internal head of the gastrocnemius, which usually commu- 

 nicates with the joint and sends a prolongation between the gastrocnemius and the 

 semimembranosus. This is the most important posterior bursa. (2) There is one 

 beneath the tendons of the sartorius, gracilis, and semitendinosus muscles. (3) One 

 beneath the tendon of the semimembranosus, between it and the tibia; it rarely 

 communicates with the knee-joint. (4) One between the tendons of the semimem- 

 branosus and the semitendinosus. 



Ganglion. Sometimes a rounded tumor that is called a ganglion appears in the 

 popliteal space. When the knee is flexed it is felt as a round, movable tumor which 

 is hard and cystic. If the knee is extended it slides inward to the edge of the inner 

 condyle and becomes hard and fixed. It usually originates from the bursa beneath 

 the inner head of the gastrocnemius, 

 is prolonged between it and the semi- 

 membranosus, and, when the knee is 

 flexed, it either disappears entirely by 

 its contents going into the joint or it 

 can still be felt in the popliteal space. 

 It may be a difficult matter to excise 

 these cysts on account of their ramifi- 

 cations, and when this is impossible it 

 is better to open them up, clean them 

 out, and then sew the wound shut 

 in order to avoid infecting the joint. 

 Care should be taken not to mistake 

 them for solid tumors or enlarged 

 lymph-nodes, both of which are less 

 common than ganglion. 



Fracture of the Patella. 



TI_ .'11 u r J FIG. 550. Housemaid's knee or enlargement of the prepatel- 



The patella may be fractured in two i ar bursa. 



ways, producing different lesions and 



requiring different treatment. Fracture is produced either by muscular contraction 



or by direct violence ; the former is the more common. 



Fracture by Indirect Violence. As pointed out by Humphry, when the knee 

 is fully flexed only the upper third or fourth of the articular surface of the patella is 

 in contact with the condyles of the femur the remaining two-thirds or three-fourths 

 of the projecting portion of the bone resting on the pad of fat. When semi-flexed 

 the greater part of its surface is in contact with the condyles, or at least the whole of 

 its middle third. In full extension only the lower third or fourth or even less remains 

 in contact. 



When semi-flexed the patella is subjected to the greatest leverage strain; hence 

 it is that fractures most often occur in this position and that the fracture occurs so 

 frequently at the junction of the lower and middle portions. When the bone is frac- 

 tured by indirect force (muscular) the line of fracture traverses its whole thickness 

 and consequently the joint is always involved. Usually there are but two fragments. 

 The extent of separation depends on the amount of laceration of the capsule on each 

 side of the line of fracture (Fig. 551). 



On each side of the patella the fibrous expansion of the quadriceps tendon, fascia 

 lata, and joint capsule, if intact, will prevent separation of the fragments. If it is rup- 

 tured widely it will permit a separation of about 2.5 cm. (i in.). It is rare that the 

 primary injury produces a wider separation, and those cases in which the fragments 



