tailieunhanh - Ebook Principles of deformity correction: Part 2

(BQ) Part 2 book “Principles of deformity correction” has contents: Six-Axis deformity analysis and correction, consequences of malalignment, malalignment due to ligamentous laxity of the knee, ankle and foot considerations, sagittal plane knee considerations, and other contents. | 1111 CHAPTER 12 Six-Axis Deformity Analysis and Correction In previous chapters, we defined deformity components and divided them into angulation, rotation, translation, and length. Angulation and rotation are angular deformities, measured in degrees. Translation and length are displacement deformities, measured in distance units (., millimeters, inches, etc.). In Chap. 9, we discussed how angulation (axis in the transverse [x-y] plane) and rotation (axial [z] axis) deformities can be resolved three-dimensionally and characterized by a single vector (ACA) inclined out of the transverse plane (characterized by x,y,z coordinates). Similarly, translation (displacement in the transverse plane) and length (displacement axially) can be combined into a single displacement vector inclined out of the transverse plane (characterized by x,y,z coordinates). Deformity between two bone segments can be fully characterized by three projected angles (rotations) and three projected displacements (translations). Therefore, six deformity parameters are required to define a single bone deformity. Mathematically, it is necessary to assign positive and negative values to each rotation and each translation, depending on the direction of rotation of each angle and the direction of displacement of each translation. The signs (+I-) of these angles and translations are determined by the mathematical convention of coordinate axes and the right-hand rule. The unique position of an object (bone segment) can be determined by locating three non-collinear points on that object. One segment can be moved with respect to another by translating along three orthogonal axes and rotating about these same three axes. The final position after three orthogonal translations is independent of the order undertaken. The final position after three orthogonal rotations is dependent on the order or sequence undertaken (~ Fig. 12-1). Stated more formally, rotation is not commutative. Deformity analysis, as .