534 



APPLIED ANATOMY. 



or fibular nerve; on the inner side the most prominent tendon is the semitendinosus 

 with the semimembranosus beneath and the gracilis to the inner side. 



THE KNEE-JOINT. 



As the functions of the lower extremity are support and mobility, it is evident 

 that in order to obtain mobility without unduly weakening the limb the ligament- 

 ous connection of the bones must be exceptionally strong. The knee is placed 

 half way down the extremity, hence it has the bulk of the body above to support ; 

 also, the bones on each side of the joint are the longest in the body, hence their lever 

 action is exceptionally great, which likewise necessitates that the joint be firmly braced 

 by ligaments. 



The Movements of the Knee. The knee is primarily a hinge-joint; its main 

 movements are extension and flexion. It can be extended to a straight line (180 



degrees) and flexed until the thigh 

 and upper portion of the leg come 

 in contact, at about 45 degrees or even 

 less. The movement is a combined 

 gliding and rolling one. According 

 to Morris (" Joints," p. 375), as ex- 

 treme extension ends the leg rotates 

 a little outward through a longitudi- 

 nal axis, passing through the middle 

 of the outer condyle of the femur, and 

 as flexion begins it rotates inward. 

 These rotatory movements are, 

 however, slight, and may practically 

 be ignored. When flexion has pro- 

 ceeded to 1 50 or 155 degrees, the joint 

 becomes comparatively loose, and 

 this increases as the joint is flexed, 

 until a rotation of 36 degrees (Morris) 

 is allowed. This is of decided prac- 

 tical importance because injuries and 

 treatment are intimately associated 

 with the presence of rotatory move- 

 ments. No rotation is possible when 

 the knee is fully extended, the bones 

 being then immovable. 



Bones of the Knee-joint. 

 The knee-joint is between the femur, 

 the tibia, and the patella; the fibula 

 does not enter into it (Fig. 544). The 

 patella is only a sesamoid bone de- 

 veloped in the quadriceps tendon, and 

 is not essential. In some of the lower 

 animals it has a synovial membrane 

 separate from the knee-joint proper. 

 The joint between the femur and 

 tibia is built up of two separate lateral 

 parts; the condyle and tuberosity of 

 each side forming practically a sepa- 

 rate joint and having a crucial liga- 



FIG. 544. Antero-external view of the bones of the knee. ment as one of its lateral ligaments. 



The object of thus combining two 



joints side by side to form one joint is to add to its strength and lateral stability. 

 The condyles of the femur have their articular surfaces prolonged up on its anterior 

 surface, not to aid in flexion and extension, but simply to facilitate the action of the 

 patella. The outer condyle is the higher, to prevent external luxation of the patella. 



Line of epiphysis 



External condyle 

 Patella 



Internal tuberosity 

 External tuberosity 



Head of fibula 

 Line of epiphyses 



- Tibial tubercle 



