Specialty Exam results-

Radiographs

The purpose of taking radiographs in this case was to look for evidence to support and refine our hypotheses of cranial cruciate rupture, neoplasia, and Lyme disease induced degenerative joint disease. 

Because cranial cruciate rupture is not a radiographic diagnosis, we were specifically looking for secondary osteoarthritic changes that would influence our prognosis and treatment of the injury. Specific indications of degenerative joint disease associated with cranial cruciate rupture include osteophytes, especially around the distal patella, the supratrochlear region and the tibial and femoral margins. 

There is no evidence of any osteophytes associated with the cranial cruciate ligament.  This is consistent with the history of recent (5 days ago) injury because it takes weeks to develop visible radiographic changes. We did see a small osteophyte in the area of the medial collateral ligament, but we considered it insignificant because we did not see any other signs indicating collateral ligament damage. 

A lack of other radiographic signs such as subchondral bone sclerosis, narrowing of medial and/or lateral joint space, flattening of the articular surfaces, and valgus/varus deformities suggests that significant degenerative changes have not yet occurred for radiographic detection.

If a synovial cell sarcoma was present, we would expect to see a radiodense area indicating a mass. Even though we can tell from palpation that there is no large mass present, there would likely be some evidence of invasion of the joint capsule by neoplastic cells. We saw no evidence of this.
 
There is increased fluid density within the joint and displacement of the infrapatellar fat pad cranially. These are signs of intra-articular effusion. Increased fluid can be due to vascular leakage subsequent to inflammation or increased production of synovial fluid by traumatized synoviocytes. This could support either the Lyme disease or cranial cruciate rupture hypothesis, but because of the cranial drawer sign, the cruciate theory seems more likely. The only way to definitively rule out Lyme Disease would be measuring a 4-fold increase in antibody titer between blood samples taken 3 weeks apart, but these tests have not been run on Bonnie.

Bonnie has an especially deep intercondylar fossa in her femur. This is most likely normal for Bonnie, and because the fossa does not seem narrowed, we do not think that the fossa is interfering with the cruciate ligaments in any way that would cause pathology.

We saw decreased joint space medially on the anterior posterior view, which could indicate meniscal injury. This will be further explored during surgery, however the perceived abnormality could just be due to positioning.

Clinical Pathology

There is a slight leukocytosis, which we assume to be due to a neutrophilia because all the other WBC types are within normal ranges and we have no neutrophil count. This is indicative of inflammation and would be expected with either Lyme Disease or cranial cruciate rupture. 

There is a very slight hypoalbuminemia and hypocalcemia. Since calcium is associated with albumin, any decrease in albumin would be expected to cause a decrease in measured calcium. Functionally, the animal probably has a normal amount of unbound and active calcium. The hypoalbuminemia is most likely insignificant because of its proximity to normal values and there are no other signs indicating a significant protein losing problem. We hypothesize that some of the albumin could be leaking into the stifle joint, but we don't have a measure of joint protein levels to confirm this.

The lack of hypergammaglobulinemia indicates that Lyme Disease is unlikely. At the point in the progression of the disease that we would start to see clinical signs in the joints, we would also expect to see antibodies being produced.

Joint Fluid Analysis

The reddish color indicates the presence of red blood cells, but the clarity of the fluid indicates that there aren't very many present.  Low numbers of red cells would be consistent with leakage of blood vessels caused by inflammatory mediators, or by iatrogenic hemorrhage as a result of needle insertion into the joint. The presence of neutrophils and monocytes indicates inflammation and the demand for phagocytes to "clean up" the joint. Because of the increased cell count, this fluid would be classified as a modified transudate. No bacteria are seen, so sepsis is not supported. The good mucin clot indicates that there is still an adequate amount of hyaluronic acid present. This is a favorable sign that the degeneration has not progressed to destruction of the subsynovial layer.