Biomechanical Comparison Between Porous Ti6Al4V Block and Tumor Prosthesis UHMWPE Block for the Treatment of Distal Femur Bone Defects

Abstract

Purpose: The management of bone defects is a crucial content of total knee revision. This study compared the biomechanical performance of porous Ti6Al4V block and tumor prosthesis UHMWPE block in treating distal femoral bone defects. Methods: The finite element models of AORI type 3 distal femoral bone defect treated with porous Ti6Al4V block and UHMWPE block were established. Sensitivity analysis was performed to obtain the appropriate mesh size. The biomechanical performance of treatment methods in bone defects were evaluated according to the peak stress, the Von Mises stress distribution, and the average stresses of regions of interest under the condition of standing on one foot and flexion of the knee. Statistical analysis was conducted by independent samples t-test in SPSS (p < 0.05). Results: In the standing on one-foot state, the peak stress of the porous Ti6Al4V block was 12.42 MPa and that of the UHMWPE block was 19.97 MPa, which is close to its yield stress (21 MPa). Meanwhile, the stress distribution of the UHMWPE block was uneven. In the flexion state, the peak stress of the porous Ti6Al4V block was 16.28 MPa, while that of the UHMWPE block was 14.82 MPa. Compared with the porous Ti6Al4V block group, the average stress of the region of interest in UHMWPE block group was higher in the standing on one foot state and lower in the flexion state (p < 0.05). Conclusion: More uniform stress distribution was identified in the porous Ti6Al4V block application which could reserve more bone. On the contrary, uneven stress distribution and a larger high-stress concentration area were found in the UHMWPE block. Hence, the porous Ti6Al4V block is recommended for the treatment of AORI type 3 distal femoral bone defect.

Keywords: UHMWPE block; bone defect; distal femur; finite element analysis; metal block; total knee revision.

FIGURE 1

Material properties of the inhomogeneous femur. The femur was divided into ten material properties with ten different colors. ρ: Bone density; E: Elastic modulus.

FIGURE 2

The finite element models of all components. (A) Porous Ti6Al4V block and customized prosthesis assembled to simulate the operation. (B) CCK prosthesis. (C) customized prosthesis which includes a UHMWPE block. (D) Porous Ti6Al4V block. (E, F) Distal femur osteotomy models, which are paired with porous Ti6Al4V block and UHMWPE block.

FIGURE 3

The final finite element model of surgical procedures. (A, B): Loads and constraint conditions on the femur. F1 and F2 represent the force on the medial and lateral femur, respectively. (C) all points of the proximal femur are limited to 0 in six degrees of freedom. (D) forces are applied to the “Rigid body element three” area in Hypermesh, which can make the force more uniform.

FIGURE 4

The regions of interest (ROI) definition of the two groups’ models. The blue areas of (A, B) were the selected regions of interest, located in the same 10 mm femoral scale above the UHMWPE block.

FIGURE 5

Von Mises stress distribution of blocks under different conditions. (A) and (B) are the stress distributions of porous Ti6Al4V Block and UHMWPE Block in the standing state, respectively. (C) and (D) are their stress distribution in the flexing state.

FIGURE 6

Von Mises stress distribution of femur. The figure shows the stress distribution of femurs in different groups during the standing and flexion stages.

FIGURE 7

Von Mises stress distribution of different prostheses. The Von Mises stress distribution on the prostheses and its maximum stress under different loading patterns.