RECONSTRUCTION OF NONCONTAINED DISTAL FEMORAL DEFECTS WITH POLYMETHYLMETHACRYLATE AND CROSSED- SCREW AUGMENTATION

Abstract

Background: Curettage and cementation with polymethylmethacrylate are frequently used in the treatment of aggressive benign bone lesions such as giant-cell tumors, but strength and stiffness of the reconstructed bone have been concerns. This biomechanical study was undertaken to determine whether augmenting the cement with crossed screws would result in a stronger reconstruction. Methods: Large noncontained defects were created in the medial femoral condyles of twenty matched pairs of human cadavera. Four groups were organized to compare three types of reconstruction: (1) polymethylmethacrylate alone, (2) polymethylmethacrylate and intramedullary Steinmann pins, and (3) polymethylmethacrylate with crossed screws engaging the opposite cortex. The specimens were subjected to 2000 compressive cycles and were subsequently monotonically loaded to failure under a controlled displacement rate. Failure load and stiffness were determined for each femur that survived the cycling process. Results: Femora reconstructed with crossed screws and cement failed at higher loads and had greater stiffness than those reconstructed with cement alone (p = 0.025 and p = 0.0007) or cement augmented with intramedullary Steinmann pins (p = 0.019). Failure of femora reconstructed with cement and crossed screws occurred through an extra-articular transverse fracture, while failure in those with cement alone and cement with Steinmann pins occurred through an intra-articular (intercondylar) fracture. Conclusions: In this in vitro cadaver study, augmentation of polymethylmethacrylate cement with crossed screws resulted in a stronger reconstruction of distal femoral tumor defects than that obtained with cement alone or with cement and intramedullary Steinmann pins. Clinical Relevance: The stronger and stiffer construct of cement augmented with crossed screws might allow earlier walking and rehabilitation after tumor resection, with a decreased risk of fracture after reconstruction. Should a fracture occur after reconstruction with polymethylmethacrylate and crossed screws, the results of this study suggest that the fracture is likely to be extra-articular, which can be treated with standard fracture-fixation methods.