PRACTICAL CONSIDERATIONS : THE CLAVICLE. 259 



movement exists, and the fore-limbs are used only in progression, no cla\'icle, or a 

 mere rudiment of it, is present. 



Congenital absence of both clavicles is rare. In several reported cases the 

 shoulders could be brought together in front of the body. The congenital absence 

 of both acromial ends is not so uncommon. Theoretically, one would expect, as a 

 result of absence of the clavicle, a weakened upper extremity, some lateral curvature 

 of the spine, interference with the upper chest (from the weight of the arm and 

 scapula), and hence diminished lung capacity with the secondary ill effects upon 

 growth, nutrition, etc. 



Such consequences were predicated (Maunder) as a result of arrest of growth 

 from epiphyseal separation, but neither in those cases, in non-union after fracture, 

 nor in congenital absence have they been noted. On the contrary, in the four 

 cases of symmetrical absence of the acromial end recorded by Gegenbaur the func- 

 tional disability was slight, the motions of the scapula being unimpaired. 



The whole bofie becomes ossified very early, beginning before any other long 

 bone of the skeleton. Its one epiphysis, at the sternal end, is, on the contrary, the 

 last of the epiphyses of the long bones to ossify, appearing about the seventeenth or 

 eighteenth year and, according to Poland, joining the diaphysis from the twenty- 

 second to the twenty-fifth year. Dwight places the time of union somewhat earlier. 



Separation of this epiphysis is among the rarest of epiphyseal detachments. 

 But five cases have been recorded. Two of them were from muscular action, the 

 pectoralis major and the clavicular fibres of the deltoid being apparently the agencies 

 that carried the sternal end of the diaphysis forward. 



The age of the patient (from seventeen to twenty-five), the shape of the flattened 

 diaphyseal end (unlike the pointed end of a fractured bone), and the integrity of the 

 shape of the suprasternal notch aid in distinguishing this accident from a forward 

 dislocation or a fracture on the inner side of the costo-clavicular ligament. 



Fracture of the clavicle is more common than that of any other bone, except possi- 

 bly the radius ; it is, likewise, the most frequent seat of incomplete ( " greenstick" ) 

 fracture. About one-half of all clavicular fractures occur during early childhood. 

 This frequency is due (i) to the early ossification of the bone, so that it is relatively 

 more brittle than are the other bones ; (2) to the lack of close attachment between 

 the periosteum and the bone ; (3) to the unusual thickness of the periosteum (prob- 

 ably associated with the early ossification), which tends to prevent complete fracture ; 

 and (4) to the common occurrence of falls and minor accidents among children. 



The amount of disability is often surprisingly slight, and the diagnosis, unless 

 confirmed by skiagraphic testimony, may have to be made on the basis of very trifling 

 deformity with localized tenderness and swelling. 



Muscular action may produce fracture through the violent contraction of the 

 pectoralis major or of the clavicular portion of the deltoid. 



Indirect violence (received through falls on the hand, elbow, or shoulder) is 

 the common cause. The frequency with which such falls occur, and the uniformity 

 with which the force is transmitted to a slender bone containing but little cancellous 

 tissue, and held firmly at either end by strong ligamentous attachments, sufficiently 

 explain the common occurrence of clavicular fracture. 



The break usually occurs about the junction of the middle and outer thirds, 

 because: (i ) the outer end (like the inner) is firmly held by the ligamentous connec- 

 tions, the middle of the bone being the most movable ; (2) at the outer end of the 

 middle third the bone is smaller, and therefore weaker ; (3) at this point the sternal 

 curve (convex forward) and the acromial curve (concave forward) meet, and force 

 applied to the extremity of the bone is there expended. 



Fracture of the clavicle is rarely compound, because, although the bone is sub- 

 cutaneous, the skin is very freely movable over it, and because the usual displace- 

 ment carries the sharp end of the outer fragment backward and the sharp end of 

 the inner fragment upward (Fig. 278). 



The anatomical causes of the common form of displacement will be considered 

 in connection with the muscles concerned (page 579). 



The relations of the clavicle to great vessels and nerve-trunks would seem to 

 render frequent complications probable, but as a matter of fact the latter occur with 



