444 SURGICAL APPLIED ANATOMY. [Chap. xxi. 



patella irjiisi* Jbe -JiQm through. : 'Ind^ed/^one but a 

 slight separation of the parts is possible until that ex- 

 pansion is .ruptu/ed- Braune has 'tfemonef.r&ted this 

 by experiment, fy sawing through fche patella without 

 damage to the lateral ligameiitous structures, and 

 noting that but trifling separation of the fragments 

 was possible until these structures had been divided. 

 In stellate fractures, due to direct violence, these 

 fibrous expansions from the extensor tendon may be 

 uninjured, and no separation of any magnitude be per- 

 mitted between the portions of the broken bone. 



The patella is more readily broken by muscular 

 violence than is either the extensor tendon or the liga- 

 mentum patellae. In the flexed position it will be seen 

 (Fig. 48) that the bone is placed at a considerable 

 disadvantage when compared with the two other 

 structures. Bichet reports a case where violent con- 

 traction of the quadriceps caused the tubercle of the 

 tibia to be torn away from the bone without any other 

 lesion of the parts immediately concerned being 

 produced. 



Dislocation of tlie patella. This bone may 

 be dislocated outwards or inwards, or turned upon its 

 edge so that its anterior and posterior surfaces are 

 placed laterally. The luxation outwards is by far the 

 most common. This depends upon the fact that the 

 quadriceps, the patella, and the ligamentum patellae do 

 not, when the muscle is contracted, follow the lines of. 

 the femur and tibia. They are more nearly in a 

 straight line, that passes to the outer side of the angle 

 formed by the femur with the leg at the knee-joint. 

 Muscular contraction, therefore, tends to draw the 

 knee-cap outwards, a tendency that is in all normal 

 circumstances corrected by the increased prominence 

 of the external condyle. The vastus externus also is 

 said to be more powerful than the internus. 



Dislocations of this bone are usually due to 



