Hypothesis 1ÑHyperextension Deformities

Immature foal with lack of development of all muscles that contribute to the calconeal 
tendon (gastronemius, semitendinous, biceps femoris, superficial and deep digital flexors).    

The flexor muscles have not yet hypertrophied so they are small and inadequate

In adequate strength of flexor muscles places sub-optimal amounts of tension on the 
calconeal, superficial and deep digital flexor tendons.  This lack tension permits 
hyperextension of fetlock joint.  

Inactivity of the fetus in utero may have predisposed the foal to this condition.  Fetal 
movement in utero is important to promote adequate muscle development to support normal 
tension on flexor tendons.