Operative Techniques in Foot and Ankle Surgery
■ Deformities which cannot be corrected at the CORA as well as for large corrections, a dome-shaped osteotomy should be considered in order to avoid excessive translation of the distal fragment. ■ Congruent joints should be considered for dome-shaped osteotomies; incongruent joints usually qualify for wedge osteotomies. ■ In case of a wedge osteotomy: ■ Valgus deformities are usually addressed with a medial closing wedge osteotomy. ■ Varus malalignment is corrected with a medial opening wedge osteotomy or a lateral closing wedge osteotomy. ■ For all corrections of the distal tibia, a correction of the length and position of the fibula must be considered in order to preserve ankle joint congruency. ■ The most important aspect of the preoperative planning is the assessment of the origin of the deformity. Different enti- ties need to be distinguished, and it is mandatory to separate the isolated frontal plane deformity of the hindfoot from complex deformities involving the transverse, sagittal, and coronal planes with or without muscular dysfunction and imbalanced ligamentous structures. ■ Distinction of congruent and incongruent joints ( FIG 1 ) is helpful in determining the type of osteotomy performed (tibia only vs. tibia and fibula; wedge osteotomy vs. dome- shaped osteotomy).
■ To determine the size of the wedge that should be added or removed to restore anatomic alignment in the ankle, the tibiotalar angle should be measured. ■ On a standard anteroposterior image of the ankle joint, the tibiotalar angle is the angle between the tibial axis and the tibial joint surface. The wedge to be corrected can be measured out of the radiographs or calculated with the mathematical formula tan H/W, where is the angle to be corrected, H is the wedge height in millimeters, and W is the tibial width ( FIG 2 ). ■ An overcorrection of 3 to 5 degrees is recommended by most authors for asymmetric osteoarthritis. ■ Additional deviation (eg, rotational or translational defor- mities) must be taken into consideration during the planning of the osteotomy.
■ Positioning of the patient depends on the surgical approach:
■ Anterior approach: supine position
■ Lateral approach: lateral decubitus position or supine with a sandbag under the buttock of the affected limb ■ Medial approach: supine, ipsilateral knee in slight flexion with a sandbag under the calf
■ An anterior, lateral, or medial approach can be chosen to correct the deformity. The choice depends on the nature of the defor- mity, the local soft tissue conditions, and previous approaches.
FIG 1 ● An illustration of a congruent ( left ) and an incongruent ( right ) joint. In congruent joints, the joint space between tibia and talus is paral- lel despite the distal tibial joint surface angle being in a varus or valgus deviation. In incongruent joints, the talus is tilted within the ankle mortise.
FIG 2 ● Planning of the correction: measuring the deformity and plan- ning the wedge size that should be inserted ( lower line of the white triangle indicating the level of the osteotomy).
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