Chap, xi.] THE STERNO-CLAVICULAR JOINT. 197 



the only articulation that directly connects the upper 

 limb with the trunk, yet it is possessed of such con- 

 siderable strength that luxation at the joint is com- 

 paratively rare. The amount of movement in the 

 joint depends to a great extent upon the lack of 

 adaptability between the facet on the sternum and 

 the sternal end of the clavicle. The disproportion 

 between these parts is maintained by the inter- 

 articular cartilage, which reproduces only the outline 

 of the clavicular surface. The cavity of the joint is 

 V-shaped, since the clavicle only touches the socket 

 at its inferior angle when the arm hangs by the side. 

 When the arm is elevated, however, the two bones are 

 brought in more immediate contact, and the joint 

 cavity becomes a mere slit. Thus, in disease of this 

 articulation it will be found that of all movements of 

 the joint the movement of the limb upwards is the 

 most constant in producing pain. The joint is sup- 

 plied by the suprasternal nerve. 



The movements permitted at this joint are 

 limited, owing to the anterior and posterior sterno- 

 clavicular ligaments being moderately tense in all 

 positions of the clavicle. Movement forwards of the 

 clavicle on the sternum is checked by the posterior 

 ligament, and resisted by the anterior ligament. This 

 latter ligament is more lax and less substantial than 

 is the posterior band. Its weakness serves in part 

 to explain the frequency of the dislocation forwards. 



Movement of the clavicle backwards on the 

 sternum is checked by the anterior ligament, while 

 the passage of the head of the bone is resisted by the 

 powerful posterior band. The movement is also 

 opposed by the rhomboid ligament. To produce, 

 therefore, a dislocation backwards considerable force 

 must be used. Movement of the clavicle upwards on 

 the sternum is checked by the rhomboid ligament, the 

 interclavicular ligament, the interarticular cartilage, 



