Diagnosis:

	Rupture of the left cranial cruciate ligament.

	Diagnosis of a cranial cruciate rupture is based on a thorough history, physical 
exam, and radiographs.  ÒBonnieÓ is a highly active dog, which places a great deal of 
strain and pressure on her joints.  ÒBonnieÕsÓ acute partial weight-bearing lameness of the 
left hindleg suggests that the rupture was due to degenerative changes in the cranial 
cruciate ligament. Aging and degeneration of the cranial cruciate ligament is related to 
size. Dogs greater then 15 kg show more changes and have a more significant change in 
cranial cruciate ligament strength than do smaller dogs.  Also, it has been shown 
consistently that dogs greater than 5 years old have a decrease in material properties.  
ÒBonnieÓ is 6 years old and overweight.  Her signalment supports degenerative rupture.  
ÒBonnieÕs is susceptible to cranial cruciate rupture because she is in poor physical 
condition, obese, and has improperly conditioned muscles.  ÒBonnieÓ is lacking the 
protection from excessive stressors on her knee. 
	
There are two ways to rupture or tear the cranial cruciate rupture.  The first is 
associated with violent internal rotation of the tibia.  The function of the ligament is 
consraint of the joint motion, limiting internal rotation of the tibia.  If violent rotation 
occurs, the caudo-medial edge of the lateral femoral condyle can cause damage to the 
ligament as it rotates against the condyle.  This type of rotation could occur if Bonnie 
were to spin on a planted limb.  The second way to damage the cranial crucial ligament is 
by hyperextension of the stifle.  In this case, the roof of the intercondylar notch can act as 
a knife and sever the ligament.  ÒBonnieÓ could have hyperextended her stifle by any 
excessive motion during her normal physical activity.  Running, jumping, chasing, 
fetching and climbing stairs could all cause hyperextension.

	On physical exam, there is effusion of the left stifle joint with a distention of the 
joint capsule on either side of the straight patellar ligament.  There is pain on 
manipulation of the stifle.  These physical exam findings are typically seen in a cranial 
cruciate rupture.  When the ligament is torn or ruptured, inflammation and hemorrhage 
results. The released inflammatory mediators cause an increased in vascular permeability 
resulting in joint effusion and distention of the joint capsule.  This elicits pain, which is 
manifested by lameness.  The joint cytology rules out sepsis and immune-mediated 
disease.  The effusion is characterized as a nonseptic modified transudate with evidence 
of hemorrhage and inflammation.  A 4-5 mm cranial drawer of the left stifle was palpated 
while under sedation.  This finding is diagnostic for rupture of the cranial cruciate 
ligament.

	The radiographic findings rule out osteoarthritis and neoplasia.  There was 
evidence of joint effusion with capsular distention.  The lateral view of the left stifle 
showed compression of the infra patellar fat pad.  The anterior-posterior view showed an 
increased in joint space laterally between the femur and tibia.  No degenerative changes 
were found on either view supporting a recent rupture.  Degenerative changes of the bone 
occur within a few weeks and severe changes occur within a few months.