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Changes of bone structure within the hip joints have been examined using two radiographs within a period of 1 to 10 years in 147 Airedale Terriers and 82 Golden Retrievers to verify their significance in the diagnosis of hip dysplasia. Primary as well as secondary features for dysplasia were often developed only discretly mainly in B (suspicious) or C (nuld HD) evaluated hips and frequently difficult to distinguish from individual conformational or technical influenced variations Since subluxation can not always be demonstrated reliably, secondary reactive signs of dysplasia were found as important indicators for functional joint disruption.Approximately only one third of the B or C classified hip joints of Golden Retrievers older than 5 years of age had developed definite coxarthritis, in joints evaluated as moderate dysplasia (D) already 83%. More than one third of the images taken from the young dog, however, showed initial "arthritic" bone structures but had developed no degenerative joint disease (DJD) on the followup radiographs. In the Airedale Terrier (all of them younger than 5 years) approximately a quarter of the B but two thirds of the C hips were presumed to be in early stages of DJD.It was observed that certain joint structures frequently altered in varying degrees depending on the individual as well as on the breed. Sorne of thern did not show any acute reaction even in clearly established arthritis. Ihe most definite evidence for early stages of coxarthritis in this study was the "Morgan line". More than 80% of Golden Retriever hip joints showing those well defined, vertically orientated ridges of new bone extending from the base of the neck towards the trochanteric fossa had developed DJD on the second radiograph. Most of the B classified Airedale hips with that "Morgan line"" showed initial degenerative processes and half of them had to be evaluated as dysplastic a year later. A similar close relationship was established between the development of arthritis and structural changes at the cranial effective acetabular rim. Sorne hips with a significant acetabular rim, however, were misdiagnosed due to poor radiographic quality.Frequently, especiaIly in the Airedale Terrier, a sclerotic line in ring formation could be noticed distally and parallel to the groth plate. In most cases, however, those hip joints did not show any degenerative radiolographic changes. But since it was seen m both breeds when either DJD was obvious or joints free of arthritis appeared with mild dysplastic signs (e.g. shallow acetabulum or instability) the formation of this line may represent condensation of trabecular bone as a reaction of stretched capsule fibres for joint stabilisation. A visible ring formation, however, does not seern to lead to degenerative joint disease as frequently as the Morgan line.Unsuitable technical equipment (e. g. coarse or damaged grids or intensifying screens), under- or overexposure and poor film developing techniques as well as even simple positioning defects reduced the information provided by the radiograph significantly, especiaIly the diagnosis of minor secondary dysplasia signs. The cranial acetabular edge, the discrete bony deposits around the femoral head and neck as well as the cranial effective acetabular rim were particularly susceptible to lacks of image qualityPrimary characteristics of dysplasia were diagnosed more reliably on relatively poor radiographs although the extend of maximal laxity - as e. g. measured by the Norberg-Olsson-Angle - could not be demonstrated in all cases with conventional radiographic techniques. On more than a quarter of all Airedale hips angle differences of more than 4ºon both radiographs could be detected. Although a valuable diagnostic tool as an equivalent of possible instability, the Norberg angle is loosing its importance with higher measurements: 9% of the Airedale hips without any signs of DJD had to be evaluated C or D on the followup radiograph because of the evidence of subluxation. Nevertheless a low Norberg angle was correlated more frequently with arthritic processes than it was when higher angles were measured, even though remarkable frequency of coxarthritis could be found in joints with Norberg angels about 105" but other signs for dysplasia (Airedale Terrier 25%, Golden Retriever 37%).In order to recognize mild dysplastic joints attention has also to be paid to the size of the femoral head in relation to the acetabulum as well as to adequate cover of the head by the dorsal acetabular edge because even minor abnormal covering caused bony reactions.Despite the improvement of the radiographic quality during this study only 9% of the 395 radiographs which were submitted for official evaluation allowed the depiction of aß even of the more subtle joint structures. Obviously the technical quality of the radiographs influenced the judgement reliability. 34% of the Airedale Terriers received a different report when re-examind one year later, 15% (21/139) first classified B hips showed definite dysplasia on the followup radiograph.The estimation of evident structure deviation into reactive, early degenerative, anatomical variation or technical artefact was very difficult in cases with only slight primary dysplastic signs and led in some cases to unreliable classification.Despite the mentioned limitations secondary dysplastic changes as signs of functional instability and beginning of degenerative joint disease remain of great importance. Therefore an excellent radiographic technique must be expected, which allows the depiction of all joint structures and even of minor abnormalities.