Chap, xi.] STER NO-CLAVICULAR JOINT. 199 



diseased structures from being kept at rest, (2) by the 

 occasional persistence of the interarticular cartilage, 

 and (3) by the utter lack of adaptability of the two 

 bony surfaces involved. 



Dislocations of the sterno-clavicular joint. 

 The clavicle may be dislocated from the sternum in 

 one of three directions, which, given in order of fre- 

 quency, are : (1) forwards, (2) backwards, (3) upwards. 

 The relative frequency of these dislocations can be 

 understood from what has been already said as to the 

 action of the ligaments in restricting movements. 

 The displacement forwards involves entire rupture 

 of the capsule, and more or less damage to the 

 rhomboid ligament. The head of the bone carry- 

 ing with it the sterno-mastoid, rests on the front 

 of the manubrium. The dislocation backwards 

 may be due to direct or indirect violence, and 

 has occurred spontaneously in connection with the 

 chest deformity in Pott's disease. The capsule is 

 entirely torn, as is also the rhomboid ligament. The 

 head is found in the connective tissue behind the 

 stemo-hyoid and sterno-thyroid muscles. In this 

 position it may cause severe dyspnoea, or dysphagia, 

 by pressure upon the trachea or gullet. It may so 

 compress the subclavian artery as to arrest the pulse 

 at the wrist, or so occlude the bi'achio-cephalic vein as 

 to produce semi-coma (Fig. 17). In one case the head 

 of the bone had to be excised to relieve a troublesome 

 dysphagia. In the luxation upwards, due usually to 

 indirect violence, the head rests on the upper border 

 of the sternum between the sterno-mastoid and sterno- 

 hyoid muscles. It involves more or less complete 

 tearing of all the ligaments of the joint, together with 

 avulsion of the interarticular nbro-cartilage. 



The non-adaptability of the joint surfaces in this 

 part serves to explain the ease with which these 

 luxations are usually reduced, and the difficulty 



