RINGBONE 113 



Dollar attributes the frequency with which this joint is affected with 

 ringbone to its anatomical formation, and states that " to act as an in- 

 complete ginglymoid joint its area must necessarily be limited and its 

 articular surface flat." A reference to our anatomical description of the 

 joint will enable us to dismiss at once the latter portion of this statement. 



The antero-posterior curves formed by the surfaces with which the 

 distal extremities of the large metacarpal and suffraginis articulate are 

 very similar. In the former case the articulation is continued from the 

 suffraginis on to the sesamoid bones, and in the latter case there is a similar 

 continuation on to the complementary cartilage from the upper surface of 

 the corona. Now the cartilage is fixed to the top of the corona, whereas 

 the sesamoid bones, over which a considerable amount of the concussion 

 is received at the fetlock joint, are suspended at the back of the joint, and 

 afford the joint a considerable degree of elasticity. A contributory 

 factor which enables the sesamoid bones to receive a fair share of the con- 

 cussion is the angle at which the long axes of the large metacarpal bone 

 and suffraginis meet. That the pastern joint is more commonly affected 

 with arthritis than the fetlock may be attributed to this compensatory 

 distribution of the concussion over the sesamoids in the latter. 



The acceptance of this view favours the belief of Percival that ring- 

 bone is most commonly found in animals with upright pasterns. The 

 more upright the suffraginis and coronas are placed, the less the pressure 

 upon the complementary cartilage, and the greater the shock experienced 

 by the articular surfaces of the suffraginis and the corons when weight is 

 placed upon the limb. Other writers, including Peters and W. Williams, 

 favour the view that long weak pasterns are more predisposed to the 

 affection on account of the greater strain thrown upon the ligaments. In 

 joints so formed there is manifestly much greater tension on the ligaments, 

 but this predisposes to the formation of those exostoses near the points 

 of insertion of the ligaments, which exostoses we have excluded from the 

 category of true ringbone, and which are dealt with elsewhere in the 

 chapter on Bones. 



