Predicting proximal femur rotation by morphological analyses using translucent 3-dimensional computed tomography

Abstract

Predicting rotation of proximal femur in femur fracture surgeries is important to prevent malrotation. We aimed to prevent malrotation by developing a simple guideline that enables the prediction of proximal femur rotation using translucent 3-dimensional computed tomography (3D CT). Retrospective. One tertiary general hospital in the Republic of Korea. Thirty-six subjects who underwent CT angiographies for vascular evaluation. Translucent 3D CT images were created from the CT data. Morphologic ratios of the great trochanter (GT) and lesser trochanter (LT) with the hip center as a basic point were measured at neutral position and at 5°, 10°, 15°, 20°, 25°, and 30° of internal rotation (IR) and external rotation (ER). The rotation angles at which the GT ratio becomes 0.5 and 0.33 and the rotation angles at which the LT ratio becomes 0.0 and 1.0 were determined to serve as guide angles. Both the proportion of GT and LT compared with proximal femur with hip center as a reference (GT and LT ratio) gradually increased in the shift from IR to ER. At a neutral position, the GT and LT ratios were approximately 0.4 and 0.5, respectively. At 10°-15° of ER, the approximate GT and LT ratios were 0.5 and 1.0, respectively. At 30° of ER, the GT ratio exceeded 0.6, and the LT ratio exceeded 1.0. Between 10° and 15° of IR, the GT ratio decreased to approximately 0.33 and the LT ratio decreased to 0.0, which indicated that the LT was invisible. We suggested practical values which might be useful as a reference in the operating room practically and hope that our findings would be helpful to prevent malrotation while performing proximal femur or femur shaft surgeries.