Page 394 - Canine Lameness

366 20 Hip Region

Gatineau et al. (2012) found an increased DAS to be correlated to an increased risk of developing
OA. Though it should be noted, the DAS was most predictive when the DI was >0.7.
Another measurement used to quantitatively evaluate HD is the NA. To make this measurement
a hip extended ventrodorsal view is used. First, a line is drawn connecting the centers of the femo-
ral heads, then a line is drawn from the center of the femoral head to the ipsilateral craniolateral
acetabular rim. If the NA 105°, it is considered normal. However, Gaspar et al. (2016) compared
NA to DI and dorsolateral subluxation score and found that a cutoff of 105° was not highly predic-
tive for HD suggesting that a much higher angle should be used, such as 112° in order to predict
laxity in dogs with a DI of 0.3.
Distraction radiography appears to hold more promise to screen animals for HD compared to
hip-extended radiographs (Verhoeven et al. 2012). Evidence of hip laxity remains the most predica-
tive risk factor for the development of OA in dysplastic hips (Smith et al. 2001). In the future, blood
sample testing may simplify screening for HD, though a DNA test that recently became available
was found to be of low diagnostic value (Ginja et al. 2015; Manz et al. 2017).
In older dogs with OA who have sudden worsening of one side, or present with toe touching to
non-weight-bearing lameness, cranial cruciate ligament rupture, sepsis, or neoplasia should be con-
sidered as a differential diagnosis. Radiographs of dogs with severe OA can be difficult to differentiate
from infection and/or neoplasia (Figure 20.16). In these cases, arthrocentesis may assist in making a
definitive diagnosis. Additional imaging with CT scan may also be useful. If warranted, arthroscopy,
ultrasound or CT guided biopsy can be performed as well (Butler and Gambino 2017).

20.6 Avascular Necrosis of the Femoral Head

Avascular necrosis of the femoral head is known by many names: Legg-Perthes, Calve-Perthes,
Legg-Calvé-Perthes, aseptic necrosis of the femoral head, osteochondritis juvenilis, and coxa
HIP REGION head and neck of small-breed dogs, causing a noninflammatory aseptic necrosis. The definitive
plana (Demko and McLaughlin 2005). It is a disease affecting the vascularity of the femoral

etiology of the disease is not known; however, several theories have been proposed including
anatomic conformation, deficiency in blood clotting factors, hereditary factors, hormonal
imbalances, infection, infarction and obstruction of the venous drainage of the femoral head
and neck, and trauma.
Regardless of the exact etiology, the progression of the disease is well delineated. Initially, the
compromise to the blood supply leads to ischemia and necrosis of the femoral head. This is fol-
lowed by an attempt at repair with fibrovascular tissue. Due to the underlying compromise to the
bone, subsequent repeated forces on the bone cause fissures and clefts to develop in the articular
cartilage of the femoral head, leading to collapse of the subchondral bone and flattening of the
femoral head. The damage to the joint surface will eventually lead to the development of OA.
Conservative treatment with pain management is only reported to be adequate in 25% of cases,
thus surgical intervention with femoral head and neck ostectomy or total hip arthroplasty is typi-
cally recommended.

20.6.1 Signalment and History
Numerous breeds have been reported as being afflicted with the disease, with toy breeds and
terriers being predisposed to developing avascular necrosis of the femoral head. It has been deter-
mined to be an autosomal recessive trait in the miniature poodle and the West Highland white