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Fig. 2 | Journal of Orthopaedic Surgery and Research

Fig. 2

From: Postoperative excessive external femoral rotation in revision total hip arthroplasty is associated with muscle weakness in iliopsoas and gluteus medius and risk for hip dislocation

Fig. 2

Computed tomography (CT) measurements of femoral rotation angle, impingement distance, and muscle size and density. A Functional stem anteversion or external rotation angle of the femur was measured by subtracting the value for the rotation angle of the superior anterior iliac spine line from that of the stem angle (β–α) or angle of the posterior femoral condyle axis (γ–α) using a CT image acquired within a month of surgery. The posterior pelvis–stem or pelvis–femur distances were measured by drawing a circle and by measuring the shortest distance from the stem to the pelvis (X) or from the femur to pelvis (Y) at the lower level of the artificial head in a cross-sectional CT image acquired after surgery. B Using preoperative CT images, the psoas muscle was detected at the upper edge of the iliac crest, and the iliac, gluteus medius, and gluteus maximus muscles were detected at the level of the mid-point between the iliac crest and great trochanter. A calibration phantom was placed during the CT scan and utilized to adjust the CT density, which was measured in Hounsfield units. (Gmed, gluteus medius; Gmax, gluteus maximus)

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