64 THE GROWTH OF BONE 



According to some Gennan and French observa- 

 tions, blood-clot has an influence not only in pro- 

 viding a suitable medium in which bone may be 

 formed, but further, in exerting a direct chemical 

 stimulus upon the osteoblasts. 



We may now appl)^ these researches to surgical 

 practice, considering first the consequences and 

 repair of fractures. In subperiosteal fractures, rapid 

 and firm union takes place without any ensheathing 

 callus, and the bone feels quite normal after a few 

 months. When the periosteum is extensively torn, 

 osteoblasts wander out beyond its limits, and en- 

 sheathing callus may be formed in quantity. Much 

 will depend on the amount of movement to which 

 the part is subjected. Vigorous movement, or, in 

 those cases where the periosteum is stripped away, 

 deep massage applied too early just over the site of 

 the fracture, will disseminate the osteoblasts far and 

 wide. Not only may the callus be excessive, and, 

 perchance, lock the nearest joint, but muscles, nerves, 

 or tendons may become ensheathed by new bone, 

 and their functions be impaired. 



Here belong those interesting and by no means 

 infrequent cases in which, after a fracture, especially 

 near the elbow joint, an osseous mass develops in the 

 muscles, as for instance in the brachialis anticus. 

 This is called traumatic myositis ossificans. The mass 

 can be moved apart from the bone, and casts a 

 shadow with the A;-rays. What has happened is that 

 massage or movements have scattered the osteoblasts 

 far and wide, and they have, after a few weeks, 

 performed their usual function, and regenerated bone 



