Interpretation:

Complete blood count:  A mild leukocytosis is seen.  This is due to an acute 
inflammation within the stifle joint due to the rupture of the cranial cruciate ligament. 
There is a hypoalbuminemia accompanied by a hypocalcemia. The hypoalbuminemia is 
due to the inflammatory process within the joint.  The capillaries become leaky due to the 
infiltrate of inflammatory mediators and albumin is allowed to leak into the interstitium 
causing the hypoalbuminemia.  The hypocalcemia can be explained by the fact that 40% 
of the circulating calcium is bound to albumin.  The resulting hypocalcemia is due to the 
loss of the albumin and the calcium that was bound to it.  There are no clinical signs of 
hypocalcemia which support this fact.

Joint fluid analysis: The fluid is reddish-clear which is suggestive of a nonseptic 
modified transudate.  The red color can be attributed to hemorrhage within the joint from 
the ligament rupture.  The cell count is 3500 per high powered field.  Most of the cells are 
neutrophils and monocytes.  This is due to the inflammatory response causing migration 
of these leukocytes into the joint space.  There is no bacteria present which would rule 
out an infection within the joint. There is a good mucin clot.

Radiographs of the stifle:  Lateral view: No degenerative changes were noted within the 
femur or tibia. There is intracapsular swelling evident.  The infrapatellar fat pad is 
displaced cranially which is caused by the inflammatory response.  
AP view: This view does not show any degenerative changes on the femur or tibia.  
There is an increase in joint space laterally between the femoral and tibial condyles.  
There is decreased joint space medially between the medial condyles of the femur and 
tibia.  The cranial cruciate ligament holds the lateral condyle of the femur very closely 
and firmly to the medial condyle of the tibia.  If this ligament ruptures you would expect 
to see the changes in the joint space as described previously.  There is more stress placed 
medially on the joint which is another supporting factor of the decreased joint space.
If this were a chronic ligament rupture we would expect to see ligament tears including 
osteophyte formation along the trochlear ridge, caudal surface of the tibial plateau and 
inferior pole of the patella.  Thickening of the medial fibrous joint capsule and 
subchondral sclerosis would also be evident.