Varization open-wedge osteotomy of the distal femur: comparison between locking plate and angle blade plate constructs.

Purpose: Biomechanical properties of locking plate and angle blade plate constructs in opening-wedge distal femur osteotomy were compared, with special attention to the impact of opposite cortex breakage and buttressing.

Methods: Forty-eight synthetic femora underwent a lateral opening-wedge distal femur osteotomy, which was fixed either with a locking plate or with an angle blade plate. Two main groups were constituted based on the integrity of the opposite medial cortex-intact medial cortex and fractured medial cortex (FMC). Axial compression and torsion tests were performed comparing stiffness of all bone-implant constructs. In the group FMC, a special subgroup has been tested taking into consideration the effect of placing an additional 6.5-mm cancellous screw buttressing the medial cortex. Statistical level of significance was fixed in 0.05 using a confidence interval of 95 %.

Results: Intact medial cortex significantly increased the stiffness for both implants tested in this study. In the FMC group, angle blade plate constructs reached higher stiffness mean values for both torsion and axial compression. The insertion of a buttressing screw on the medial cortex increased the stiffness of all tested bone-plate constructs. This additional screw favoured mostly locking plate constructs implementing their stiffness to torsion to mean values comparable to those reached by angle blade plate constructs.

Conclusions: Angle blade plate constructs reached higher stiffness mean values than locking plates for both axial compression and torsion loads. The addition of a buttressing screw on the opposite cortex increased the stability of all bone-implant constructs to levels similar to those showed with an intact medial cortex. The present study findings support the clinical use of angle blade plates, alone or associated with a medial buttressing screw, as an alternative fixation method for supracondylar open-wedge osteotomies of the femur.