Quantitative analysis of protective Kirschner wire diameters in lateral opening wedge distal femoral osteotomy: A finite element study

Abstract

Objectives: This study aims to investigate quantitatively the protective effect of a 1.6-mm or a 2.5-mm Kirschner wire (K-wire) on the medial hinge at different gap distances through finite element analysis (FEA) and to establish whether using a 2.5-mm K-wire can offer benefits compared to a 1.6-mm in preventing medial hinge fractures.

Materials and methods: Between June 2024 and July 2024, three different models simulating a lateral opening wedge (LOW) osteotomy of the distal femur were created from a femoral computed tomography (CT) scan of a 36-year-old male patient: no K-wire (Model I), 1.6-mm K-wire (Model II), and 2.5-mm K-wire (Model III). Finite element analysis was performed to simulate 7- to 13-mm gaps at the osteotomy site. Loads, principal stress, strain, and equivalent stress were analyzed around the medial hinge.

Results: Model I required 123.0±5.2 N, Model II required 181.7±12.2 N, and Model III required 228.7±13.6 N (p<0.001). Cracked shell elements were the lowest in Model II and the highest in Model I. While the average equivalent/yield stress ratio was not significantly lower in Model II compared to Model III (87.0±10.9% vs. 92.7±12.1%), the maximum equivalent/yield stress ratio values in Model II were significantly lower than both Model I and Model III (1206.2±138.3% vs. 1836.2±165.4% and 1689.1±404.0%, respectively), suggesting a superior dispersion of forces.

Conclusion: Using a 1.6-mm K-wire during LOW osteotomy of the distal femur provides a balance between structural reinforcement and stress distribution, significantly improving stability and reducing the risk of medial hinge fractures compared to a 2.5-mm K-wire or no K-wire. The 1.6-mm K-wire optimizes stress dispersion, making it the preferred choice for surgical planning in lateral opening wedge distal femoral osteotomy.

Figure 1. (a) Base osteotomy model. (b) Osteotomy model with a 1.6-mm K-wire. (c) Osteotomy model with a 2.5-mm K-wire.

Figure 2. Graphical representation of Young's modulus of the individual elements on top of the corresponding computed tomography slice.

Figure 3. Loading and boundary conditions. Distal femur was fixed at the proximal end and load was applied perpendicularly at the osteotomy site.

Figure 4. Region of interest at the hinge area to extract biomechanical data.

Figure 5. Results for solid elements. (a) Average principal stress at each gap distance. (b) Average principal/critical stress percent at each distance. (c)Average equivalent stress at each gap distance. (d) Average equivalent/yield stress percent at each distance.

Figure 6. Results for shell elements. (a) Average principal stress at each gap distance for shell elements. (b) Average principal/ critical stress percent at each distance shell elements. (c) Average equivalent stress at each gap distance shell elements. (d) Average equivalent/yield stress percent at each distance shell elements.

Figure 7. Visualization of the protection of a K-wire at the hinge site. (a) Tensile forces are dispersed around the wire. (b) No K-wire results in concentrated stresses. (c) Tensile stresses on the K-wire.