Plan of Action:

Radiographs-  At least two views of the stifle will be taken at 90 degree angles to each 
other.  Obvious signs of trauma will be looked for; fracture, avulsion fracture associated 
with ligament rupture.  Neoplasia must also be considered.  You would expect to see an 
aggressive radiographic appearance with a primary, malignant neoplasia of the  bone or 
joint.  There may be focal soft tissue swelling, bone lysis, a “sunburst” appearance due to 
tumor production, a long transition zone between normal and affected bone, and 
pathologic fractures.  If neoplasia is suspected from the stifle radiographs, thoracic 
radiographs must be taken to look for sites of metastasis.  Radiographic signs of 
infectious arthritis are joint effusion, periarticular bone lysis, and irregular bone surfaces 
with subchondral bone erosion and sclerosis.  With osteoarthritis/DJD, we would look for 
narrowing of the joint space, periarticular osteophyte formations, sclerosis or cystic 
changes in subchondral bone, enthesophytes at sites of attachment, and increased joint 
fluid.  With ligament damage such as rupture of the cranial cruciate ligament, you may 
only see joint effusion and possible avulsion fracture.  Stress radiographs using a shearing 
stress can be taken that will demonstrate degree of displacement of the tibia relative to 
the femur.  This shearing stress is the same type of manipulation applied during the test 
for the cranial drawer sign.

Joint tap analysis-  The joint fluid that was tapped should now be analyzed.  With cranial 
cruciate ligament rupture, you may see cellular increases indicative of inflammation and 
hemarthrosis due to local hemorrhage.  Changes with osteoarthritis/DJD will probably be 
unremarkable, or may show slight changes in cell counts.  Septic arthritis may yield 
grossly purulent joint fluid, and white blood cell counts, especially neutrophils, will be 
elevated.  Non-degenerate neutrophils and even bacteria may be present.
 
CBC- A CBC is always good practice to look for other things that may be going on in the 
animal, especially if surgery under general anesthesia is a consideration for treatment.  
With septic arthritis, you would look for an inflammatory leukogram.  No changes would 
be expected with any of the other hypotheses.

Culture and Sensitivity-  If your results were leading you towards septic arthritis at this 
point, you would want to go ahead and do a culture and sensitivity.  This will be 
important in deciding treatment.

Arthroscopy-  If neoplasia, arthritis, and other injuries are ruled out, arthroscopy can be 
diagnostic for cranial cruciate ligament rupture.  However, the cranial drawer sign is 
probably enough for a diagnosis.  This requires specialized equipment that many mid-
range practices will not have.

Ultrasound-  Same as for above, can help with diagnosis, but many practices do not have 
the equipment, and probably is not necessary.