Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 577
Fig. 4-129 A 10-month-old female Chihuahua with an
intermittent lameness involving both rear limbs. Patella
luxation was identified clinically. Radiographs of both stifles
were taken. A, In the right stifle the patella is located
medially in the posteroanterior radiograph. It appears to
be in its normal position in the lateral radiograph. The
right femoral condyles appear larger than the left. The
tibial crest is somewhat medially displaced; however, the
degree of displacement and severity of the bowing deformity
are much less than that seen in the left stifle. B, In
the left stifle the patella is displaced medially, is located
medial to the femur on the posteroanterior radiograph,
and is superimposed upon the distal femur in the lateral
radiograph (arrow). The tibial crest is rotated medially,
and the femoral condyles are hypoplastic. There is a bowing
deformity of the proximal tibia. Diagnosis: Bilateral
medial patella dislocation. The changes are severe on the
left and moderate on the right. There is no evidence of
degenerative joint disease at this time.
A
B
moid) deformity with a hypoplastic medial femoral condyle, shallow trochlear groove, and
medially positioned tibial crest. In severe cases, especially in larger dogs, secondary degenerative
joint disease may be present.
Lateral patellar luxation is uncommon but may be observed in large-breed dogs. It
is observed in some breeds as a conformational deformity but also may occur secondary
to stifle trauma. Radiography is essential for evaluating the severity of the limb
deformity and identifying the presence of fractures or secondary degenerative joint
disease.
Osteonecrosis of the Femoral Head. Osteonecrosis of the femoral head, or Legg-Calvé-
Perthes disease, may occur spontaneously in young toy and small-breed dogs (4 to 11
months old), or may be secondary to intracapsular femoral neck or capital physeal fractures.
589-594 The condition has been shown to be inherited in Yorkshire and West Highland
White Terriers. 593 Early radiographic signs include increased density in the femoral head