2 week old intact, female, bay thoroughbred foal- The signament is important because it is a young animal.  Neoplasia, arthritis and degenerative changes not likely.

nursing normally- Foal probably received an adequate amount of colostrum.  Don't have to worry about failure of passive transfer of immunity.  Joint ill not likely.

mare is current on vaccinations- If mare was current for vaccinations, foal probably got proper immunity through colostrum

foal has not been vaccinated or dewormed- Still too young to receive vaccinations, under the influence of mare's immunity.

mare and foal part of small herd- There is exposure to other horses besides the mare, and possibility of other trauma.

T- 101.8 -Normal, systemic infection not likely.
P- 60- Within the normal range for a foal (60-80).
R- 52- A little high for a foal (20-40).  However, the foal is probably excited and this may be the reason. 

Bright and alert, all systems ok except musculoskeletal- The fetlock problem is the only observed abnormality in this foal.

swollen right hind fetlock- The apparent problem is in the fetlock.

very lame on right hind and refuses to use- Non-weight bearing lameness, severe.

owner thinks mare stepped on foal's leg- Possible cause for trauma. Don't hone in only on this though, could be other causes for the problem

toe touching lameness on right rear limb- This indicates a non-weight bearing, continous lamness that we would classify as a grade IV.

soft tissue swelling/pitting edema sitting 12 cm proximal to fetlock and extending just distal- Theer is significant edema dur to fluid accumulation.  Causes could be fracture, soft tissue changes, inflammation due to infection...

she resents palpation of the limb- There is significant pain associated with the fetlock

no foreign body- No noticable penetration of foreign object that may have caused the problem.

no resentment of hoof testers- Problem not with the coffin bone or hoof. We are localizing the lameness to the fetlock.

following exam, foal more lame and does not put foot on ground- Manipulation of the joint (flexure or digital pressure) exacerbated the lameness.  This could be a positive test which would localize the lameness to the fetlock, but we do not know how many joints were manipulated by the veterinarian.

no instability or crepitance upon palpation- Crepitus is caused by the grating of fractured bone fragments against each other or the noise produced by pressure on tissues containing an abnormal amount of air.  Just because there is not crepitance, we can not rule out fracture without radiographs.