Benign bone tumors occur mainly in the epi-metaphyseal region of long bones, and surgery is the most effective treatment. Tumor recurrence and fractures are complications of following surgery. To reduce the risk of these complications, preoperative surgical simulation is recommended. This study uses FEA to investigate the mechanical effect of reconstructed models with different fillers. The simulations are considered for two defects of different sizes in the medial femoral condyle. The small defect simulates tumor curettage and the large defect simulates tumor curettage with some border texture. The fillers include several polymers, ceramics, and bioglasses. The mechanical performance of each filler in the reconstruction of defects under single-leg standing loading is evaluated by examining the maximum principal and von Mises stresses compared to the healthy model. In the epi-metaphyseal region of the healthy model, the maximum principal stress was 5.15 MPa and the maximum von Mises stress was 7.63 MPa. Among the materials tested, polyether ether ketone (PEEK) exhibits stress values very close to healthy bone. (with the values of the principal and von Mises stresses was 5.14 MPa and 7.66 MPa in the small defect and 5.16 MPa and 7.7 MPa in the large defect, respectively). However, Hydroxyapatite (HA), Beta-tricalcium phosphate and bioglasses showed the least mechanical compliance, which increased with increasing defect size. Comparison of the results obtained shows that the choice of filler depends on the size of the defect. These findings highlight the role of FEA in predicting surgical outcomes and postoperative bone strength.