Specialty Exam Results:

Clinical Pathology -

Bonnie's CBC and blood chemistry report showed a slight leukocytosis without a left shift, a slight hypocalcemia and a hypoalbuminemia.  Patients with hypoalbuminemia often exhibit a concurrent hypocalcemia because 40% of the measured serum calcium is bound to albumin.  Because only the unbound, ionized calcium is the biologically active form, the hypocalcemia with a concurrent hypoalbuminemia is usually clinically insignificant.  Using a mathematical formula to figure out the adjusted calcium levels (adjusted Calcium = measured Calcium + (3.5 - measured albumin)) we discovered that the adjusted calcium concentration is really 10.7 mg/dl which is within normal limits.   The hypoalbuminemia seen in this case could be due to decreased production or increased loss.  Since we do not have a panhypoproteinemia we can rule out decreased production by the liver and maldigestion.  Therefore, the hypoalbuminemia in this case is probably due to increased loss of albumin into the stifle joint effusion.  Increased blood flow and capillary leakage in this area would lead to albumin leakage into the site of injury.  Bonnie also had a slight leukocytosis with a probable neutrophilia. Our clinical pathology report does not indicate the neutrophil concentration, but we can assume that the leukocytosis is due to a neutrophilia because there is not a monocytosis or lymhpocytosis.  This can be explained by glucocorticoid release due to a pain response.  Glucocorticoids are released by the adrenal glands in response to stress.  This causes a decreased margination of phagocytes as well as an increased release of neutrophils from the bone marrow's storage pool.  This leads to the leukocytosis seen in this case.

Joint Fluid Analysis -

The fluid in this joint tap is classified as a hydroarthrosis.  The normal joint synovial fluid contains 500 to 3000 nucleated cells per ml with considerable variation between individuals.  Bonnie's joint tap showed as slightly elevated cell count (3500).  Hydrarthrosis is usually associated with a non hemorrhagic joint trauma such as a ligamentous stretch or tear causing accumulation of watery fluid into the joint.  This watery fluid may actually dilute out the nucleated cells present, leading to a cell count that will look lower than it actually is. The lack of macrophages indicates that this is not a chronic process.  Chronic joint diseases will have large numbers of macrophages with abundant cytoplasm indicating active phagocytosis.  Bonnie's joint fluid contained only neutrophils and monocytes which are present in acute inflammatory processes.  The fluid reddish in color which is insignificant in this case because one cannot rule out iatrogenic hemorrhage when the joint tap was performed.  We would need a red blood cell and/or platelet count of the joint fluid to accurately diagnose the cause of the reddish fluid.  The fact that the fluid is clear indicates a low cellularity or a very dilute fluid.  This joint fluid also had a good mucin clot indicating the absence of hyaluronidase secreting bacteria.  Mucin clots are also an indirect indication of synovial fluid viscosity.  This further confirms a non-septic joint as the absence of visible bacteria in a joint tap is not always significant.  Many times bacteria will colonize the joint capsule and will not be obtained in a routine joint tap.  


Radiograph Analysis:  

There is a generalized opacity given to the entire stifle joint space due to the joint effusion. Due to this increased opacity, the infrapatellar fat pad is difficult to visualize and its location with respect to the joint capsule is hard to determine.  However, we believe that the fat pad is pushed proximally and dorsally due to intracapsular swelling.  There is no indication of an avulsion fragment of the cranial cruciate ligament.  No osteophytes were found on any of the common places expected with OCD. These include the medial and lateral trochlear ridges or the distal border of the patella, the proximal border of the patella or the proximal tibia.  The margins of the proximal tibia show no sclerosis, which, given the lack of other characteristic changes, indicates that there are no degenerative joint changes present.  We see an increased separation between the tibia and femur on the lateral surface of the stifle joint and a decreased separation on the medial side.  This is the result of the instability with a ruptured cranial cruciate ligament.  There is no evidence of a fracture or bone lysis congruent with osteosarcoma.