THE STIFLE JOINT 95 



tibia, through the medium of the two interv^ening fibro-cartilaginous 

 discs. 



The articulation of the patella is on the trochlea, which is at the 

 front of the femur. This trochlea is made up of two parallel ovoid 

 ridges, which run in an almost vertical direction. The upper ex- 

 tremity of the inner ridge is very much more massive than that of the 

 outer, and it also extends to a higher level. This is a point of clinical 

 importance, since it renders the dislocation of the patella in the internal 

 direction a very difficult matter. 



The outer ridge has a sharp, well-defined anterior edge, whilst that 

 of the inner ridge is blunt and smooth. These ridges are separated from 

 one another by a groove, and the groove, together with the surfaces of 

 the ridges which bound it, is articular. 



The posterior surface of the patella presents an articular face which 

 is moulded, though somewhat imperfectly, upon the articular portion of 

 the trochlea which has just been described. It thus presents a mesial 

 ridge which separates two vertical shallow grooves. In accordance with 

 the larger size of the inner lip of the trochlea, the inner depression on 

 the patella is much the broader. In addition, the area of this depression 

 is increased by a fibrocartilaginous thickening of the internal straight 

 patellar ligament. The movement of the trochlea on the patella is in a 

 vertical plane. 



The parts of the femur which enter into the femoro-tibial joint are 

 the condyles. These are two ovoid convexities which run parallel to 

 one another in the antero-posterior direction. They are separated by 

 a deep notch called the intercondyloid groove which is non-articular, 

 and which, in the articulated limb, accommodates the upwardly pro- 

 jecting piece of bone at the superior extremity of the tibia termed the 

 spine. 



