B. Gladbach et al., The treatment of leg-length-discrepancy and frontal-plane-deformities withthe percutaneous epiphyseodesis technique, ORTHOPADE, 28(12), 1999, pp. 1023-1033
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.