Group 11 - Learning Issues

1. What exactly is involved in the cranial drawer test?  The thumb
and index finger surround the caudal distal femur (fabellar region) and
proximal patella while the other thumb and index finger surround the tibial
crest and caudal fibular head.  The leg is flexed slightly and the femur is
held steady while the tibia is pushed directly cranially and caudally,
swiftly and gently.  The manipulation is repeated in extension and flexion.
In the majority of animals the greatest amount of drawer movement occurs
when the stifle is in slight flexion because this is the functional
position of the limb.  In addition, sedation is also necessary to obtain an
accurate test because pain can elicit a reflexive tightening of the stifle
that can decrease or eliminate evidence of instability.  Also, with chronic
degenerative changes drawer motion may be imperceptible due to periarticular tissue thickening and fibrosis.
2. What is the significance of the 4-5mm and 2mm cranial drawer signs in Bonnie's left and right stifles, respectively?  	One reference indicates that displacement of less than 2mm is a normal cranial drawer.  Displacement of greater than 2 but less than 4 mm indicates a partial cranial cruciate ligament (CrCL) rupture and 4-5 mm drawer indicates complete CrCL rupture.  Those values suggest that Bonnie likely has a left (unilateral) complete CrCL rupture.  The other references we consulted steered clear of specific numbers, and spoke in relative terms (e.g. normal vs. abnormal).  It seems clear, keeping all information in mind, that in all likelihood Bonnie does have either a partial or complete rupture of her left CrCL.
3. It was not indicated whether the cranial drawer tests were done on flexion or extension of the joints, however what would it tell us if the test were positive in one or the other of these positions?  Often a partial tear or stretching of the CrCL results in a increased cranial drawer on flexion of the stifle, minimal movement in the 140 degree position, and no cranial drawer in the extended position.  This implies that a positive cranial drawer test on both flexion and extension indicates that a complete CrCL rupture is more likely.
4. What may we expect to find on evaluation of the joint tap?  Abnormal joint taps often have an increased amount of joint fluid and various changes in the numbers of mononuclear cells, neutrophils, and the presence of other organisms such as bacteria.  Below is a table of expected findings for various conditions:
Normal: 250-3000 nucleated cells/mm^3 ; 94-100 mononuclear ; 0-6 neutrophils
DJD:    1000-5000 nucl. cells/mm^3 ; 88-100 mono. ; 0-12 neutro.
Erosive arthritis: 8000-38000 nucl.cells/mm^3 ; 20-80 mono. ; 20-80 neutro.
Nonerosive arthritis: 4400-371000 nucl. cells/mm^3 ; 5-85 mono. ; 15-95 neutro.
Septic arthritis: 40000-267000 nucl. cells/mm^3 ; 1-10 mono. ; 90-99 neutro.
5. What type of diagnostic tests could be performed to further evaluate
this lameness?  See plan of action for the outcome of this learning issue.
6. What are the functions of the cranial cruciate ligament and how does
this relate to the mechanisms of injury?  	The function of the CrCL is
to constrain the stifle joint so as to limit the normal internal and
cranial displacement of the tibia relative to the femur and to prevent
hyperextension of the stifle.  Most often the ligament is injured when the
stifle is rotated quickly with the joint in 20 to 50 degrees of flexion or
when the joint is forcefully hyperextended.  The former happens when the
animal suddenly turns toward the limb with the foot firmly planted causing
extreme internal rotation of the tibia with stress on the CrCL.
Hyperextension probably often occurs by stepping in a hole at a fast gait.
7. What are the attachments of the cranial cruciate ligament?  	The
proximal attachment is a fossa on the caudal aspect of the medial side of
the lateral femoral condyle.  The ligament then courses medially and
distally and attaches to the cranial inter-condyloid area of the tibia.
8. What are the radiographic changes found with a cranial cruciate ligament rupture?  Radiographs are rarely diagnostic for rupture of the CrCL, however radiographs can be helpful in confirming intra-articular disease.  Common findings include:  joint effusion with capsular distention and compression of the infrapatellar fat pad, periarticular osteophytes, enthesiophytes, CrCL avulsion fractures, calcification of the CrCL.
9. What are the radiographic changes found with septic arthritis?	In the early stages of the disease radiographs may indicate thickened and dense periarticular tissues, and possible synovial effusion.  In the later stages of the disease there is evidence of bone destruction including:  osteolysis, irregular joint space, discreet erosions, and periarticular osteophytes.
10. What are the radiographic changes found with degenerative joint disease? These changes may include any of the following: joint capsular distension, osteophytes, enthesiophytes, soft tissue thickening, narrowed joint spaces, and subchondral sclerosis in severely affected patients.  Osteophytes would likely be found on the trochlear ridges, caudal surface of tibial plateau, and/or the inferior pole of the patella.  
11.  What are some factors that may play a role in degenerative joint disease, or postural arthrosis of the stifle joint?  	Genetics, breed predispositions (abnormal standing angle), obesity, poor muscular conditioning with decreased suupport of intra-articular structures, abnormal conformation, females have a higher incidence, chronic hypoestrogenism due to ovariohysterectomy leading to ligament breakdown.  
12.  What types, if any, of conformational problems could result in chronic weakening and eventual rupture of the cranial cruciate ligament? 	Excessive loading on the ligament secondary to abnormal tibial conformation.  Specifically, this abnormality in anatomical structure could result in increased internal rotation or hyperextension within an animal's gait.  In addition, stenosis of the intra-condylar notch may lead to friction against the caudal aspect of the lateral femoral condyle.  
13.  What are the etiologies of septic arthritis in the canine stifle joint?  Hematogenous spread of microorganisms from a distant septic foci, extension of a primary osteomyelitis, contamination associated with traumatic injury, and iatrogenic causes.