KNEE Varization open-wedge osteotomy of the distal femur: comparison between locking plate and angle blade plate constructs Bruno Bellaguarda Batista • Jose Batista Volpon • Antonio Carlos Shimano • Mauricio Kfuri Jr Received: 22 August 2013 / Accepted: 9 April 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract 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 frac- tured 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 con- structs 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 but- tressing 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 alter- native fixation method for supracondylar open-wedge os- teotomies of the femur. Keywords Genu valgum Á Knee osteoarthritis Á Osteotomy Á Bone plate Introduction Varization osteotomy of the distal femur is a well-estab- lished procedure for young patients presenting a painful valgus knee with lateral compartment degeneration [2, 3, 6, 18, 22]. Alignment can be obtained by either medial closing-wedge technique or lateral opening-wedge tech- nique [4, 11, 14, 15, 20]. The limitation of the latter is the opposite medial cortex, which acts as a hinge, limiting the amount of correction, once its integrity is essential for maintaining stability and attained alignment [13]. In recent years, locking plates have been developed to overcome the problem of a possible opposite cortex breakage. Locking plates were used initially in high tibial osteotomies with favourable biomechanical and clinical outcomes [16]. Although locking plates perform well for osteotomies B. B. Batista Á J. B. Volpon Á A. C. Shimano Á M. Kfuri Jr Laboratory of Bioengineering, Department of Biomechanics, Medicine and Rehabilitation of the Locomotor System, School of Medicine of Ribeira ˜o Preto, University of Sa ˜o Paulo, Sa ˜o Paulo, Brazil M. Kfuri Jr (&) Knee and Orthopedic Trauma Group, School of Medicine of Ribeira ˜o Preto, University of Sa ˜o Paulo, Av. Bandeirantes 3900, 11o Andar, Ribeira ˜o Preto, SP CEP 14048-900, Brazil e-mail: kfuri@fmrp.usp.br 123 Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-2998-1