Page 391 - Canine Lameness

20.5 Hip Dysplasia 363

(A) (C) (E)

(B) (D) (F)

Figure 20.10 Radiographic views of three patients diagnosed with coxofemoral osteoarthritis secondary
to hip dysplasia displaying the radiographic progression: (A, B) juvenile patient displaying (black arrow)
severe subluxation without arthritic changes; (C, D) adult patient displaying (white arrow) arthritic changes
namely a thickened femoral head and (black arrow) subluxation; (E, F) adult patient displaying severe
osteoarthritic changes of the hip joint. Note that this patient is the only patient that displays obvious
changes on the lateral view. HIP REGION

unless luxation is present). It is important to note that in some dogs with juvenile HD, conven-
tional radiographs may not show any pathology, including a lack of subluxation/decreased cover-
age of the femoral head by the acetabulum on the ventrodorsal view. This is because maximum
hip laxity occurs in a neutral position (similar to weight-bearing standing position) and when
performing the standard leg extended radiographs, the joint capsule is twisted and forces the
femoral head into the acetabulum (also called “windup mechanism”; Figure 20.11; Heyman et al.
1993). However, as the disease progresses with age, evidence of OA will develop including periar-
ticular osteophyte formation on the femur (caudolateral curvilinear osteophyte), osteophytes on
the cranial and caudal acetabular rim, joint remodeling including flattening of the femoral head
and subchondral sclerosis of the craniodorsal aspect of the acetabulum. Often, the acetabulum
will also be shallow compared to a normal coxofemoral joint. The lateral projection may show
complete dorsal luxation of the hip joint, or loss of normal joint space, but these changes are only
observed with more severe disease.
Numerous specific radiographic assessments have been developed for evaluating dogs for HD
with two common methods including the Orthopedic Foundation for Animals (OFA) evaluation
and PennHIP (the University of Pennsylvania Hip Improvement Program) to help try and deter-
mine which dogs may develop clinical HD over time. OFA radiographic evaluation consists of