1446 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



in a fracture of the patella is due chiefly to the extent to which the lateral tendinous expansions 

 of the yasti are torn; to a less degree to the ha?morrhage from the numerous articular vessels 

 (p. 1452) and synovial effusion. The lower fragment is usually the smaller, and its fractured 

 surface tilted forward; that of the upper one usually looks backward. 



The patella, the largest of the sesamoid bones, ossifies by a centre which appears from the 

 third to the fifth year. The process is completed about puberty. The rareness with which 

 necrosis and caries occur here, when the exposed situation of the bone is remembered, is partly 



Fig. 1164. — Knee-joint as Shown by the R5ntgen-rays, Antero-posterior View. 



) 



explained by the density of its Ms.sue, e.spcri.-div in front, and t he intimate blending of the rectus 

 fibres with its periosteum. When the knee-joint is bent., the trochlear surface of the femur can 

 be made out, with some (lifficulty, underneat li the (iii;uh-iceps expansion. The upper and lateral 

 angle of this surface forms a useful iimdinark (dodlee) as a line drawn from it to the adductor 

 tubercle marks the level of the lower epipiiysis of the femur. 



Dislocation of the patella. The following anatomical facts account for this taking place 

 much more frequently laterally:— (1) The medial edge of the patella is more prominent, and 

 thus more exposed to injury; it is also well supported, as is seen when, the parts being relaxed, the 



