Prevalence of Primary Radiographic Signs of Hip Dysplasia in Dogs

SIMPLE SUMMARY: Hip dysplasia is the most common non-traumatic disease and cause of lameness in dogs. Different screening programs which use radiographic evaluation of the extended ventrodorsal projection of the hip exist for breeding selection. The Federation Cynologique International assigned five different scoring grades from A to E, ranging from a normal hip to severe dysplasia, to provide certification of the status of the joint. Of the different methods used for assessment, the Brass method is the most descriptive since it considers each part of the hip joint individually. The aim of the present study was to improve knowledge regarding the morphological changes in the context of hip dysplasia progression, especially in grades A to C. Some alterations were even found in grade A. The laxity and incongruence of the joint lead to the modification of the shape of the head and femoral neck, although some changes may be present in the normal or near normal hip joint. Some of the present findings, which were in contrast to the literature, are very interesting and additional investigation is indicated. ABSTRACT: Hip dysplasia is a disabling orthopedic disease in dogs. The aim of this retrospective study was to evaluate the morphological aspects and radiographic changes in the development of hip dysplasia in adult dogs, and to describe the frequency of each radiographic parameter according to each Fédération Cynologique Internationale (FCI) grade. Brass descriptive forms for the evaluation of hip dysplasia were obtained from the archive of the Italian Fondazione Salute Animale, and the radiographic evaluation of 642 hips were processed. Sixteen radiographic criteria were assessed, divided into six main parameters: acetabulum, femoral head and its position in the acetabulum, femoral neck, joint space, and Norberg angle. The initial mild alterations were shown in the craniolateral acetabular rim (31.8%), slightly divergent in the joint space in 58.6% of FCI-A. The spherical shape of the femoral head was mildly small/flattened in 56.9% of FCI-B, in addition to a slightly cylindrical-shaped femoral neck (60.5%) and slightly lost contours (55.0%). Changes in acetabular depth (45.0%), and in the cranial acetabular margin (56.7%) were found in FCI-C. The center of the femoral head was lateral to the dorsal acetabular rim in 70.0% of FCI-B; the Norberg angle appeared normal in 70.6% of FCI-B. Elaboration of the radiographic criteria from the Brass descriptive forms allowed for the extrapolation of accurate knowledge regarding morphologic changes in the development of dysplasia by providing detailed information for each individual. In particular, the present survey showed that the morphological alterations of the acetabulum prevailed over those of the femoral head only at the beginning of the development of canine hip dysplasia, and then worsened after the changes occurred in the femoral head and neck.