590 



HUMAN ANATOMY. 



Fractures of the humerus are much influenced by muscular action, although the 

 controlling force in the production of the deformity is often that which causes the 

 fracture. 



In fracture of the tuberosities the theoretical displacement is upward and back- 

 ward for the greater tuberosity under the action of the supra- and infraspinatus and 

 teres minor, and' forward and inward for the lesser tuberosity, which is supposed 

 to be drawn in that direction by the subscapularis. The injury is extremely rare ; 

 the clinical signs are obscure. Increased breadth of the shoulder, localized tender- 

 ness and disability, occurring after the application of direct force or after violent 

 action of the shoulder muscles, would be suggestive ; recognition of a preternaturally 

 mobile or displaced fragment would be conclusive ; but the X-rays w'ill usually be 

 essential. 



In fracture of the surgical neck of the humerus — i.e., between the tuberosities 

 and the insertions of the axillary muscles — and in separation of the upper epiphysis 

 the fragments are similarly influenced by muscular action. The upper fragment is 

 held in place, is a little elevated, and is obliquely tilted by the supra- and infraspinatus, 



subscapularis, and teres minor. 

 •riG. 573. Yhe upper end of the lower 



fragment is drawn towards the 

 chest-wall by the pectoralis 

 major, latissimus dorsi, and 

 'teres major. Their action may 

 be aided by that of the deltoid, 

 which may fix the middle of 

 the bone so that it acts as a 

 fulcrum, or may actually abduct 

 the elbow. The biceps, triceps, 

 and coraco-brachialis and del- 

 toid draw the lower fragment 

 upward, causing shortening 



(Fig. 573)- 



Epiphyseal disju7icHon may 

 be suspected if («) the patient 

 is a child or an adolescent ; 

 {b') the anterior projection of 

 the upper end of the lower frag- 

 ment is at an tmusually high 

 level, — i.e., about that of the 

 coracoid ; (/■) the crepitus is 

 mufifled ; (</) the shortening 

 is slight (page 272). The ap- 

 plication of the tests mentioned 

 above (page 583) will distin- 

 guish this lesion from luxation of the shoulder, w'hich, moreover, is very rare before 

 adult life (page 306). 



In fracture of the shaft of the humerus between the insertions of the axillary 

 muscles and that of the deltoid the upper fragment is drawn inward by the former 

 muscles ; the lower fragment is drawn upward by the biceps, triceps, and coraco- 

 brachialis, and upward and outward by the deltoid (Fig. 573). 



In fracture just below the deltoid insertion that muscle acts to such advantage in 

 abducting the upper fragment as to counteract the pull of the axillary muscles in the 

 contrary direction. The relation of the fragments will therefore chiefly depend upon 

 the direction of the line of fracture ; the shortening, under the influence of the biceps, 

 triceps, and coraco-brachialis, will depend on its degree of obliquity. In this fracture 

 it is sometimes necessary to dress the arm in abduction to overcome the deltoid con- 

 traction. 



In fracture just above the condyles (page 273) the Tine of fracture is usually 

 oblique from above downward and forward (Fig. 288). The short lower fragment 

 will be drawn upward by the biceps and triceps and backward by the latter muscle. 



Deltoid. 



tipper 

 fragment 



Long head 

 of biceps 



Lower, 

 fragment 



Pectorali 

 major, cut 

 and turned 

 down 



Pectoralis 



major (cut) 



Short head 

 of biceps 

 and coraco- 

 brachialis 



Latissimus dorsi 

 and teres major 



Dissection of fracture of surgical neck of humerus. 



