How the orientation of osteotomy in biplanar lateral closed-wedge distal femoral osteotomy influences the rotational alignment of the knee in all dimensional planes.

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Correction of coronal plane deformity by osteotomies around the knee is theoretically three-dimensional (3D) and can be associated with changes in other planes. It has been shown that 3D rotational changes are induced by biplanar high tibial osteotomy; however, relevant information in biplanar lateral closed-wedge distal femoral osteotomy (LCW-DFO) has not been reported in literatures. This study aimed to investigate rotational changes in axial and sagittal planes in LCW-DFO using computer-aided design (CAD) simulations.LCW-DFO is composed of three cuts: one ascending cut and two transverse cuts. In the simulations, the following geometrical parameters were adopted as factors potentially influencing 3D changes occurring in the osteotomy. The ascending cut angle measured as the angle between the edge of the ascending cut and the edge of the transverse cut in the lateral view, and the ascending cut obliquity measured as the angle corresponding to anterior/posterior inclination of the ascending cut with reference to the posterior condylar tangent line in the axial view. In the analysis, the effects of these bony cut angles on associated rotational changes in the axial and sagittal planes (internal/external rotation and flexion/extension) were calculated. Variation of wedge size ranged from 2 to 8 mm.The degree of the ascending cut obliquity substantially correlated with associated change in the sagittal plane (extension/flexion) while inducing only minimal change in rotation in the axial plane (internal/external rotation). When the osteotomy was made without ascending cut obliquity, the change in knee extension/flexion was minimal for the conditions analyzed while coupled internal rotation of the distal bony segment was induced.In biplanar LCW-DFO, the ascending cut angle substantially influenced the amount of internal rotation of the distal bony segment with little effect on flexion/extension angles. By contrast, ascending cut obliquity in the axial plane yields an effect on flexion/extension angles and little effect on internal rotation of the distal bony segment.

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Authors: Hiroshi Nakayama, Ryo Kanto, Tomoya Iseki, Shintaro Onishi, Shunichiro Kambara, Shinichi Yoshiya, Steffen Schröter, Toshiya Tachibana, Masaru Higa