THE REGION OF THE KNEE 463 



bones are not affected, the amount of bone removed should be 

 just sufficient to ensure firm osseous union. In these cases the 

 femur is divided just distal to the attachments of the collateral 

 ligaments, while a slice, a quarter of an inch thick, is removed 

 from the tibia. Owing to the obliquity of its long axis (p. 464), 

 the femur must be divided parallel to the line of the joint and not 

 at right angles to its axis, in order to maintain the limb in its 

 normal alignment. Since the epiphyseal lines are not interfered 

 with in either bone, the amount of permanent shortening is 

 usually slight, and it serves to prevent the foot from dragging 

 on the ground when the patient is able to walk again. 



The articular surface of the patella and the anterior articular 

 surface of the condyles should also be removed in order to 

 render the resulting ankylosis more secure. 



The posterior ligament of the joint is left intact when 

 possible, as it protects the vessels in the popliteal fossa (Fig. 

 131). The middle genicular (azygos) artery will require to be 

 ligatured as it enters the joint after piercing the ligament. 



After the anterior flap of skin and fascia has been replaced, 

 but before it is sutured, a long nail may be driven through each 

 tibial condyle into the corresponding condyle of the femur. 

 These nails should be introduced parallel to the long axis of the 

 tibia, and care must be taken lest they penetrate the popliteal 

 surface of the femur. This arrangement secures the bones in 

 position until bony union occurs. Thereafter the wound is 

 stitched up in layers. 



Genu Valgum. Under normal conditions a line drawn 

 from the centre of the femoral head to a point midway between 

 the two malleoli passes midway between the femoral condyles 

 at the knee-joint. In this way the weight of the trunk is 

 transmitted evenly to the two tibial condyles and thence to 

 the tarsal bones. 



In rickets, owing to irregular growth and ossification near 

 the epiphyseal line, the medial part of the distal extremity of 

 the femoral diaphysis may become abnormally enlarged in a 

 downward direction. As a result, the medial part of the 

 epiphysis is thrust distally so that the plane of the knee-joint 

 is directed downwards, backwards and laterally instead of 

 vertically downwards. This constitutes the condition of genu 

 valgum. A plumb-line dropped from the femoral head passes 

 to the lateral side of the centre of the knee-joint and to the 

 medial side of the centre of the ankle-joint. The deformity 



