chap, xxi.] THE REGION OF THE KNEE. 



489 



muscular action, and are most apt to occur in the ex- 

 tended position of the limb, the position in which the 

 patella is not fixed and its ligament and the anterior 

 part of the joint 

 capsule attached 

 to the bone are 

 the most lax. The 

 lateral luxations are 

 usually incomplete, 

 but may be com- 

 plete. In the 

 former case the an- 

 terior part of the 

 capsule need not be 

 torn, but in the 

 latter form it can 

 scarcely escape ex- 

 tensive rupture. 



In the disloca- 

 tion of the patella 



upon its edge, the Figr..49.-Tmnsveree Section 



. * , a joint through the centre of the 



inner boi'der of the (Braune). 

 bone usually pro- 

 jects forwards, while 

 the outer is placed 

 between the con- 

 dyles. But little 

 is known as to the mechanism of this dislocation. 



In dislocations of the knee, which are very 

 rare, the tibia may be displaced outwards, inwards, 

 forwards, or backwards. The two lateral luxations 

 appear to be more common than the antero-posterior. 

 The former are nearly always partial, the latter usually 

 complete. Considerable violence is required to produce 

 these luxations, owing to the great strength of the 

 ligaments and the great width of the bones involved. 

 Direct violence to the tibia or femur, associated often 



a, Patellae Imrsn ; ft, internal lateral ligament ami 

 inner condylc ; c. external Intend ligament 

 and outer romlyle; d, liireps; e, seiiiiiuem- 

 brannsus; /. seniitemlinosiis ; g. grnrilis 

 tendon; h, sartorius; 1, internal popliteal 

 nerve; external popliteal nerve; 3, internal 

 saplienous vein. 



