Fixator assisted lateral opening wedge osteotomy of the distal femur

Background

Lateral opening wedge distal femoral osteotomy is commonly employed in the correction of genu valgum.¹ Application of the lateral locking plate, however, is frequently impeded by the osteotomy distractor. Placing the distractor eccentrically either anteriorly or posteriorly results in transformation of the rectangular shaped osteotomy gap to a trapezoidal shape, introducing a degree of procurvatum or recurvatum to the correction respectively. Medial cortical hinge fractures introduce additional degrees of freedom, rendering rotation and angulation of the osteotomy difficult to control and correct. We describe the use of a Hoffmann mini fixator to maintain osteotomy correction accuracy during bone grafting and plate application.

Technique

A Hoffmann mini fixator is applied through a lateral incision to the anterolateral surface of the femur. Two half-pins are inserted parallel to each other and on either side of the already marked osteotomy site, at 45° to the coronal plane. The pins are connected with a short bar via two pin-to-bar connectors. The osteotomy is performed midway between the pins and opened with the osteotomy distractor to the desired correction. The pin-to-bar connectors are then tightened to preserve the achieved correction and the distractor is slid posteriorly. This maintains a symmetrical osteotomy gap while allowing unrestricted access for bone grafting of the osteotomy and application of the locking plate (Fig 1).

Figure 1.

Configuration of fixator assisted lateral opening wedge distal femoral osteotomy

Discussion

Our technique facilitates correction accuracy alongside ease of bone graft insertion and lateral locking plate application. In the event of a medial cortical hinge fracture, the half-pins may serve as reference points to ensure correct rotation at the osteotomy site.