Objective Canine hip dysplasia is a common orthopaedic disease in dogs. The Norberg angle value is a measure of hip joint laxity. The aim of this study was to quantify the degree of rotation necessary to consider the radiograph as inadequately positioned and to determine the influence of rotation on the Norberg angle.

Study Design Three sets of radiographs with different positioning and projections were acquired using 10 canine cadavers. Rotation of the pelvis was simulated by rotating the X-ray tube without changing the position of the patient.

Results In dorsoventral projections, the Norberg angle value is increased by 3.2 to 5.8%. Due to rotation along the long axis, the Norberg angle increases on one side and decreases on the contralateral side by approximately the same value. Rotation of greater than 2 degrees in a lateral direction is visually perceived by the observer as tilted. Rotation of the projection in the caudoventral to craniodorsal direction causes mild increase of the Norberg angle (≤1%), while rotation of the projection in a cranioventral to caudodorsal direction causes moderate (≤2%) decrease of the Norberg angle. Rotation of less than –10 degrees (caudoventral to craniodorsal) or greater than 10 degrees (cranioventral to caudodorsal) is visually perceived as tilted.

Conclusion Tilted images that are subjectively perceived evaluable have only little effect on the Norberg angle and are therefore probably acceptable. Dorsoventral projections can be recognized based on the proximal position of the patella and should be excluded from evaluation, as the Norberg angle value can be falsely increased.

目的 犬髋关节发育不良是犬常见的骨科疾病。诺伯格角值是髋关节松弛度的量度。本研究的目的是量化将放射线照片定位不当所需的旋转程度，并确定旋转对诺伯格角的影响。

研究设计 使用 10 具犬尸体获取三组具有不同定位和投影的 X 光照片。通过旋转X射线管而不改变患者的位置来模拟骨盆的旋转。

结果 在背腹投影中，Norberg 角值增加了 3.2% 至 5.8%。由于沿长轴旋转，诺伯格角在一侧增大，在对侧减小大约相同的值。横向方向上大于 2 度的旋转在视觉上被观察者感知为倾斜。投影在尾腹侧到颅背方向的旋转导致诺伯格角轻度增加（≤1%），而投影在颅腹侧到尾背方向的旋转导致诺伯格角中度（≤2%）减小。小于 –10 度（尾腹侧到颅背侧）或大于 10 度（颅腹侧到尾背侧）的旋转在视觉上被视为倾斜。

结论 主观感知可评估的倾斜图像对诺伯格角影响很小，因此可能是可以接受的。背腹投影可以根据髌骨的近端位置来识别，并且应该从评估中排除，因为诺伯格角值可能会错误地增加。