Chap. XL] UPPER END OF HUMERUS. 19^ 



of the displaced bone, and to be, therefore, torn when 

 those parts are disturbed. 



Fractures of the upper end of the hu- 

 merus. 1. Anatomical neck. The upper part 

 of the capsule is exactly attached to the anatomical 

 neck, and in this situation the fracture may run 

 beyond the ligament and be partly extracapsular. 

 The lower part of the capsule is inserted some little' 

 way below the anatomical neck, and in this position, 

 therefore, the lesion must be intracapsular. From 

 the line of attachment of the lower part of the capsule 

 to the humerus, fibres are reflected upwards to the 

 margin of the articular cartilage on -the head of the 

 bone. These fibres, if unruptured, may serve to con- 

 nect the fragments. If entirely separated, the head of 

 the bone must necrose, having no such source of blood 

 supply as the head of the femur derives from the 

 round ligament. It is easy for the small and com- 

 paratively dense upper fragment to be driven into the 

 wide surface of cancellous bone exposed on the upper 

 surface of the lower fragment. When impaction 

 occurs, there may be some flattening of the. deltoid, 

 since the head is rendered of less dimensions by that 

 impaction, and consequently causes a less projection of 

 the deltoid. I may be possible to detect the impac- 

 tion by examination through the axilla when the arm 

 is fully abducted. The difficulty of obtaining crepitus 

 in non-impacted fractures will be obvious when the 

 small size of the upper fragment is considered, together 

 with its great mobility, and the obstacles in the way 

 of so fixing it that one broken end may be rubbed 

 against the other. 



The amount of displacement is to be measured by 

 the laxity of the capsule. The usual deviation is a 

 projection of the upper end of the lower fragment 

 towards the anterior and inner side of the articulation, 

 brought about mainly by the muscles attached to the 



