Definition, quantification, and correction of translation deformities using long leg, frontal plane radiography

The surgical realignment of mechanical axis deviation is necessary to prevent early joint degeneration. Modern types of external fixation systems allow alignment of the mechanical axis to exact degrees. Predominately, these are corrections of angulation deformities. In some cases, the analysis of the mechanical axis deviation does not show any angulation deformity, but rather a parallel staggering of the mechanical axis lines of a bone. Such parallel staggering of the mechanical axis lines is defined as a translation deformity of the bone. In combined deformities with angulation and translation, the center of deformity can be established proximal or distal to the limit of the bone. In translation deformities, the realignment of the mechanical axis requires a parallel restaggering made by a translation-osteotomy or by a counterangulated double osteotomy. In complex deformities with angulation and translation, the translation requires separate corrective planning. In frontal plane radiographs of the standing leg, the components of angulation and translation can be established graphically or by simple trigonometric formulas. The analysis and surgical procedure to realign translation deformities or a combination of translation and angulation deformities using an unilateral fixator device are discussed.