Hypothesis 1

Fracture of the metatarsal and/or phalanx.

Mare stepped on foalÕs leg.

It is possible that the foal could have been lying down and the mare stepped on 
the 
fetlock joint of the foal causing a fracture.  This fracture could be a chip 
fracture, an 
avulsion fracture, or a more severe fracture.  With a fracture of the first 
phalanx, there is 
initially no swelling present.  However, we have no idea how long this condition 
has been 
going on.  If it happened several days ago, there would have been sufficient 
time to set up 
an inflammatory response and cause the swelling and pitting edema seen.  The 
inflammatory response due to the fracture causes a release of bradykinin which 
in turn 
causes pain upon manipulation.  This is demonstrated by the non-weight bearing 
lameness following manipulation of the joint.  This post-manipulation lameness 
could 
also appear due to the chip of bone interfering with the joint articulation and 
motion.  The 
pain that is elicited due to the fracture and inflammation could be causing an 
increased 
respiratory rate.  Inflammation is the first phase of fracture healing.  The 
trauma to the 
joint causes soft tissue damage, damage to the periosteum, and damage to the 
vessels of 
the bone.  This causes hematoma formation at the fracture ends.  Any completely 
dissociated chips or fragments are completely devoid of a blood supply which 
causes 
them to become necrotic.  The bodyÕs response to this is vasodilation and 
migration of 
inflammatory cells causing acute edema (pitting edema).  The presence of a 
hematoma 
and the extent of the fracture will be a large determining factor in 
stabilization of the 
joint.  This foals joint shows no signs of instability.