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

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.