Plan of Action

	The additional information required varies according to hypothesis.  For traumatic 
injury, the presence of fractures (or other bone abnormalities) and joint changes needs to 
be ascertained.  The existence and location of compressive lesions should also be 
determined.  For congenital abnormalities, the architecture of the stifle joint and 
associated structures should be determined and compared to normal.  
	To obtain the necessary information, a series of radiographs should be preformed, 
including craniocaudal and mediolateral stifle radiographs.  Radiographs of the left leg, to 
evaluate the pain response and for comparison, and the lumbosacral region, particularly 
looking for spinal injury and compressive lesions, should be taken.  Radiographs of the 
hip and hock may also be helpful in determining if the femur and/or tibia bow or show 
torsion, which may occur with congenital malformation.  The carnial drawer test should 
be performed under anesthesia, as a negative response on a non-aenesthetized patient is 
not conclusive.  Arthrocentesis and synovial fluid analysis are also helpful in diagnosing 
patella luxation.
	Further information should be obtained from the owner, such as the size of the 
other dog and the vigorousness of their play.