The necessity of cement augmentation in metastatic femur stabilization explored by finite element analysis.

Intramedullary nailing is widely used for prophylactic stabilization of femoral metastases. Polymethylmethacrylate (PMMA) cement augmentation is often applied, yet its biomechanical necessity across lesion sizes remains uncertain. To address this, we evaluate whether intramedullary nailing (IMN) alone provides sufficient stabilization, whether cement augmentation offers additional displacement reduction, and how it affects stress distribution in the bone and implant across varying lesion sizes. Finite element analysis is performed on femoral models simulating 1 cm, 3 cm, and 5 cm midshaft metastatic defects. Four structural conditions are analyzed: intact bone, metastasis only, IMN, and IMN with cement. Mechanical parameters including displacement, von Mises stress, micromotion, and implant stress are assessed under walking load. IMN alone reduces displacement by 31.1% and 40.1% in the 3 cm and 5 cm lesions, respectively, compared to metastasis-only models. In these larger defects, cement augmentation provides an additional reduction in micromotion of up to 8.1% and slightly lowers implant stress in the 5 cm model. In contrast, cement augmentation in 1 cm lesions increases displacement and implant stress by up to 43.8%. Therefore, the results highlight that cement augmentation provides biomechanical benefit mainly in large or structurally unstable lesions and may be unfavorable in small lesions. Intramedullary nailing alone is sufficient for smaller defects, so augmentation should be selectively applied.