Introduction: In the research work under diploma thesis we investigated the influence of different central beam courses and different positioning of the knee on the representation of anatomical structures in the anteroposterior and lateral projection. We made X-ray of the knee phantom in laboratory. By changing positions of the knee and the courses of the central beam, we determined how it affects the visibility of anatomical structures on the X-ray image. We performed knee movements in external and internal rotation. We changed the direction of the central beam in the cranial and caudal directions. Purpose: The purpose of the research analysis is to check the influence of the courses of the central beam and the positioning of the knee on the display of anatomical structures. Methods: Measurements were performed on a phantom knee at the Faculty of Medicine in Ljubljana. We did the basic anteroposterior projection of the knee, so that they were of the medial and lateral condyle of the femur from the examination table, namely 6,25 cm. The examination was divided into two parts. In the first part, we changed the position of the knee in the medial and lateral direction by 0,25 cm. We continued until we reached a distance of 3 cm from the examination table. In the second part, the positioning of the knee has not changed. We changed the inclination of the central beam in the cranial and caudal directions from five to 25 degrees. At each exposure, we changed the direction of inclination by one degree. Results: By changing positions of the knee in the medial direction, a distortion was found - an increase in anatomical structures that is not close to the image receiver. There is also an overlap of the anatomical structures of the knee. Same conclusions were obtained by changing the position of the knee in the lateral direction. By rotating the knee in the medial and lateral direction, the width of the knee joint fissure also changed, asymmetry could be observed on X-ray. By inclination of the central beam, there is determined gradual elongation of the anatomical structures of the knee. Discussion and conclusion: We conclude the for optimal X-ray analysis the patient positioning is of critical importance. If the patient's knee is rotated in the medial direction, magnification is obtained on the lateral condyles of the femur, and lateral rotation of the knee results in magnification on the medial condyle of the femur. In the caudal direction, intercondylar cavity is seen as well, with little extensions.
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