Hip dysplasia - development, recognition, control

Hip dysplasia (HD) is an inherited postnatal abnormal development of the hip joint, in which the acetabulum and the head of the femur do not fit together. In addition to primary malformations of the head of the femur and the acetabulum, the presence of a loose joint (subluxation, luxation) is also seen as an important fundamental criterion of HID. In the diagnosis of HID, there should be a differentiation between HD as a clinically relevant disease associated with pain and lameness, and its classification as a radiological diagnosis as a basis for breeding selection. The clinical relevance does not play any role in the radiographic screening used for breeding selection. For breeding selection, HD is subdivided into five categories according to the criteria of the Federation Cynologique Internationale (FCI). Depending on the presence and degree of defined radiological changes, HD is classified as A = no signs of HID, B = near normal hips, C = mild HID, D = moderate HID, and E = severe HID. The basis of the assessment is a radiograph of the hips in dorsal recumbency with extended thighs. The most important factor in the development of HID is genetic predisposition. Environmental influences (e.g. nutrition, use) can influence the development of HID in predisposed animals to a certain degree. The heritability of HD lies between 20 % and 40 %. The results of breeding selection methods are still unsatisfactory. The use of breeding values could improve the success considerably; however, these methods are often unreliable due to the frequently undertaken preselection based on the radiological screening of the hips. Alternative methods for direct and indirect selection criteria for HD are discussed in this paper. With the completion of the genome map of the dog, better methods of discerning genetically complex characteristics such as HD using molecular genetic analysis have arisen. In investigations in the German Shepherd, genetic markers have been found that can predict the inheritability of the HD and with which probability HID can occur in the older dog.