The treatment of leg-length-discrepancy and frontal-plane-deformities withthe percutaneous epiphyseodesis technique

The operative realignment of mechanical axis deviations (MAD) is necessary to prevent early joint degeneration and to reach normal load-bearing. Moder n types of external fixation systems allow an alignment of the mechanical a xis to exact degrees. Predominantly this are corrections of angular deformi ties. In some cases the analysis of the MAD does not show any angular defor mity, but a parallel staggering of the mechanical axis lines of a bone. Suc h parallel staggering of the mechanical axis lines is defined as a translat ion deformity of the bone. In combined deformities with angulation and tran slation the centre of deformity can be established proximal or distal out o f the limit of the bone. In translation deformities the realignment of the mechanical axis requires a parallel re-staggering made by a translation-ost eotomy or by a counterangulated double osteotomy. In complex deformities wi th angulation and translation, the translation requires a separate correcti ve planning. By using external fixator systems to perform acute or progress ive corrective osteotomies the position of the axis of Correction of Angula tion (ACA) in relation to the n-CORA of the deformity has to be considered. If BCA position is not conform with the n-CORA position relevant geometric effects in relation of length and translation occur. These geometric effec ts to corrective osteotomies can be calculated by using simple trigonometri c formulas or graphical methods. Possibilities to compensate translation an d length effects are shown by using unilateral external fixator systems.