Learning Issues:
 
1) How common is cranial cruciate ruptures or tears in Labradors? --Very common
2) What is a severe cranial drawer?  What is within normal limits?  What does a 
5mm cranial drawer signify? 
In a normal stifle joint no cranial drawer sign is seen, but 1-2mm of movement 
can be within normal limits.  A 4-5mm sign definitely indicates damage, either 
stretching or tearing, of the cranial drawer. 
3) What exactly causes the joint effusion?
4) What conformational defects could cause cranial cruciate rupture?