Locking plate augmentation of polymethylmethacrylate-filled distal femoral defects: A biomechanical study

Abstract

Benign, locally aggressive tumors of the distal femur are typically treated with intralesional curettage and polymethylmethacrylate (PMMA) cementation. However, it is not known whether plate fixation should be added to biomechanically augment these PMMA-filled defects. The purpose of this study was to evaluate the performance of two competing techniques for reconstruction of a distal femoral defect. For this biomechanical study, we used 12 composite femurs with properties comparable to bone. In nine femurs, identical contained medial distal femoral defects were created using a robotic arm. Group A contained three intact femurs, Group B three femurs with an unfilled defect, Group C three femurs reconstructed with PMMA alone, and Group D three femurs reconstructed with PMMA plus a medial locking plate. Locations of greatest stress concentration were determined by PhotoStress analysis, then three strain gauges were applied to each specimen at these high-stress locations. Specimens were loaded within a physiologic range followed by loading to failure. Outcome measures included construct stiffness, strain along the distal femur, and load at failure. Results showed that stiffness and strain were not significantly different between reconstructive techniques; however, both techniques reduced tensile strain along the popliteal surface by approximately 40% compared to non-reconstructed specimens. All specimens failed at the femoral neck before failing at the distal femur. These findings suggest that plate augmentation of PMMA-filled distal femoral defects like the one in this study offers insignificant biomechanical benefit within physiologic loads and therefore may be unnecessary.