-M)() JOHN C. KOCH 



lions luv I'ostorod and there is no need for excess bony material 

 t'oi- resisting th(> norninl stresses. However, if co-aptation is not 

 secured and there is a ga]) between the fractured ends of the 

 bone, union usually takes place with more or less shortening and 

 the gap is bridged in the most economical manner that the altered 

 positions of the parts of the bone will allow. The increased 

 amount of material is required because of the greater stresses 

 produced at the fracture. 



In diseased bone the gradual weakening of the bone is followed 

 by changes in form in accordance with mechanical laws : wherever 

 the stresses in the bone exceed the strength of the bone distor- 

 tion occurs until equilibrium of these lorces is attained. It is 

 clear that the essential in such cases to prevent deformity is 

 by relieving the overloaded structure as completely as possible 

 of all loads. 



Postural variations from the normal produce increased stresses 

 in certain regions and in others decreased stresses; if persist- 

 ent, such variations will produce corresponding changes in the 

 inner structure of the affected bones. In many instances there 

 results a progressive increase of deformity until a condition of 

 equilibrium is reached. 



Whenever, from any cause a persistent change occurs in the 

 manner in which loads are transmitted to the various parts of 

 the skeleton an adaptive change must occur in the inner archi- 

 tecture of the bones in which these altered conditions exist. 

 In the same manner that the application of this principle ex- 

 plains the production of deformity, it may be used to explain 

 the cure of deformity. The proper mechanical means of im- 

 posing new" mechanical conditions by which the original struc- 

 ture of bone may be restored is by the use of braces, jackets, or 

 other suitable means which over-correct the deformity, and re- 

 verse the transformation process. 



These results, so commonly secured by the orthopedic sur- 

 geon, depend upon the mathematically exact adaptation of the 

 living bone to the mechanical conditions imposed persistently 

 upon it by whatever cause or causes, and the necessary struc- 

 tural re-arrangements are usually attained with great economy 

 of material. 



