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 inflammation in this area would lead to albumin leakage into the site of injury.  This explanation could similarly explain the slight leukocytosis.  The joint fluid analysis showed an increase in monocytes and neutrophils.  Therefore there is an inflammatory process involving the stifle joint.  When the stifle was injured there was a release of inflammatory mediators that recruit phagocytes leading to an increased tissue demand for phagocytes.  The bone marrow responds to this increased tissue demand by releasing phagocytes from the neutrophil storage pool.  Because the inflammatory response is minor, only mature phagocytes were released and thus there is not a left shift.  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.  

Joint Fluid Analysis -

The fluid in this joint tap is classified as a non septic exudate.  It has a fairly high cellularity which is greater than 3,000 cells per hpf.  Most of the cells are neutrophils and monocytes which indicates an inflammatory response as explained earlier.  The reddish tint indicates the presence of red blood cells which are present due to the vasodilating effects of the inflammatory mediators.  The absence of macrophages and predominance of neutrophils indicates an acute inflammatory response.  The absence of bacteria rules out a septic joint injury.  The presence of a good mucin clot indicates that normal clotting factors and platelets are available.   This clotting ability also indicates a high protein concentration in the joint fluid, further supporting the classification of this fluid as an exudate.

Radiograph Analysis:  

There is a generalized opacity given to the entire stifle joint space due to the joint effusion. There is increased opacity of the dimension of the infrapatellar fat pad, which resembles a decreased in the dimension of its image.  There is no indication of an avulsion fragment of the cranial cruciate ligament.  There is the possibility of an osteophyte on the medial edge of the femur, unless this is a defect in the computerized image of a radiograph.  No other osteophytes were found on any of the common places expected with OCD, which includes 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 some sclerosis, which may be either a positional finding or a distortion due to the computerized image of a radiograph.  We see an increased separation between the tibia and femur on the lateral surface of the stifle joint.  This could be a positional finding or due to the fluid density separating the joint space.  There is no evidence of a fracture or bone lysis congruent with osteosarcoma.