Case 2: Diagnosis


	The orthopedic exam findings and lack of radiographic changes indicate a diagnosis of traumatic 
medial luxation of the right patella.  Titan's history of trauma (falling off the bed) with a resultant lameness 
suggests that the traumatic episode precipitated her lameness.  The fact that medial patellar luxation was 
elicited upon palpation is diagnostic for this problem.  Titan's clinical signs of a chronic, intermittent 
non-weight bearing lameness and the finding that the patella slides back into place upon flexion indicate a grade 
II/IV patellar luxation.  In this grade of luxation, a slight degree of medial tibial torsion and deviation of the 
tibial crest may be present, and the medial buttressing of Titan's stifle is consistent with this 
description.
	Medial luxation of the patella is often a congenital anomaly, especially in breeds like 
Pomeranians.  However, because Titan has a history of trauma which immediately preceded the lameness, the likely cause in 
this case was the trauma.    In congenital cases, the deformity may be associated with medial displacement 
of the quadriceps muscles, lateral torsion of the distal femur, lateral bowing of the distal one third of the 
femur, femoral epiphyseal dysplasia, rotational instability of the stifle, or tibial deformity.  These 
malformations exert abnormal torque on the developing stifle joint, resulting in deformity of the joint.  The 
cartilage may be deflected, the bones bowed from torsion, or the growth plates retarded from the abnormal 
pressure on them. These are some of the pathological changes in congenital patellar luxations.
	In a traumatic luxation, some external force causes the joint to move or stretch abnormally.  Titan 
may have damaged her quadriceps and caused it to displace medially, she may have torn the joint capsule, 
or she may have increased laxity in the patellar or possibly also the other ligaments and tendons of the stifle 
joint.  Soft tissue changes are more difficult to see on radiographs, hence the normal radiographs, and the 
fact that she experienced the trauma one year ago and has probably experienced healing of the soft tissues makes it more difficult to assess the exact nature of the 
reason for the patellar luxation other than the trauma itself.