234 



APPLIED ANATOMY. 



tudinally acting force that does it. When the transverse force acts it is expended on the 

 anterior portion of the joint because the joint is at the anterior portion of the scapula. 

 Posterior to the joint the scapula rests on the chest, so it is its anterior portion which 

 is forced inward, thus rupturing the capsule at this point. The fulcrum, or acromion 

 process, is also posterior to the midline of the joint. 



By a combination of these two forces (longitudinal and transverse) the capsule 

 is ruptured at its lower and especially its anterior portion. Its tearing is favored by 

 a twisting or external rotation of the humerus. The attachment of the capsule is 

 torn from the rim of the glenoid cavity, not from the humerus, and a fragment of the 

 bony rim frequently comes with it. The opening is large and embraces nearly or 



Prominent acromion 

 process 



Coracoid proce: 



Tense fibres of 

 the deltoid 



Prominence formed 



by the head of 



the humerus 



FIG. 246. Surface view: subcoracoid dislocation of the humerus, showing the elevation of the shoulder, 

 abduction of the arm, prominence of the displaced head below the coracoid process, flattening of the shoulder, 

 and tense fibres of the deltoid muscle. 



quite half the circumference of the joint. It is limited above by the coracoid process. 

 The cpracohumeral and superior glenohumeral ligaments lying in front of the long 

 tendon of the biceps also limit the tear upwards. If the tear does not extend so high 

 it is because the subscapularis muscle, instead of being torn, is wedged in between 

 the head and the coracoid process. Below, the tear is limited by the insertion of the 

 long head of the triceps. As the head luxates it cannot pierce the triceps tendon, 

 so it slips behind it in a posterior luxation and in front of it in an anterior luxation. 

 The supraspinatus, infraspinatus, and teres minor muscles are all posterior; they 

 blend more or less with the capsule and as the head luxates they are stretched with 

 it over the glenoid cavity. 



The long tendon of the biceps, while it may sometimes be torn loose from the 

 bicipital groove after rupture of the transverse ligament, is usually so loose that it 



