Hypothesis 1
Cranial Cruciate Ligament Rupture due to Trauma


	In the structure of the stifle, two crossed ligaments help to hold the 
femur and 
tibia in position.  These are the cranial and caudal cruciate ligaments.  These 
ligaments, 
especially the cranial cruciate, are frequently injured during stressful 
activity.  Often, a 
dog is running around the yard or chasing a cat or a squirrel and makes a sudden 
turn or 
stop, or steps in a hole.   This puts abnormal stress on the stifle joint, and 
the ligament is 
ruptured or partially torn.  When one of these ligaments is ruptured, it can 
cause pain and 
instability in the stifle joint.  The damage to the ligament causes phagocytes 
and other 
inflammatory cells to invade the joint in an attempt to clean up and repair the 
ligament.  
The inflammatory mediators which are released by the infiltrating white blood 
cells cause 
vasodilation and pain in the joint.  This increased blood flow and vascular 
leakage leads 
to joint effusion.    
The test for cruciate ligament rupture is called the cranial or caudal drawer 
sign.  
The femur is grasped firmly in one hand and the tibia in the other, and the 
examiner 
attempts to move the tibia cranially or caudally.  A cranial drawer sign of 
greater than 
about 3 mm is indicative of cranial cruciate ligament rupture.   A cranial 
drawer sign of 
less than 2 mm is normal. 
Many of the historical and clinical pieces of data fit this case.  Bonnie is a 
very 
active dog, and could have easily stressed or torn her cruciate ligament while 
jogging or 
walking with her owner.  She is also let out into a fenced backyard and likes to 
chase 
other dogs or cats.  She could have been chasing a critter in the yard and 
suffered an 
acute rupture of the ligament.   Bonnie became lame rather suddenly, and 
displays a 
partial weight bearing, toe touching lameness which is fairly typical for a CCL 
rupture.  
She has effusion and distention of the stifle joint capsule, and pain on 
manipulation of the 
joint.  While under sedation, a cranial drawer sign of 4-5mm on the left stifle 
was 
obtained, which is indicative of a CCL rupture.  The cranial drawer sign on the 
right stifle 
was normal at <2 mm.  Also, the fact that her hips, collateral ligaments, and 
patellas all 
appeared normal suggest that the cause of the lameness is most likely in the 
stifle, where 
pain and abnormalities were elicited.