Purpose <p>Distal femoral osteotomy (DFO) is an effective surgical procedure to correct valgus knee deformities. However, in lateral opening-wedge DFO (LOW-DFO), medial hinge fracture is a common complication that can lead to instability, correction loss, and delayed healing. This study aims to develop and validate a finite element (FE) model to investigate the mechanical effect of a protective Kirschner wire (K-wire) inserted in the medial hinge on the risk of hinge fracture.</p> Methods <p>A 3D finite element model of the opening stage in LOW-DFO was developed based on a prior experimental study on 3D-printed femurs. Crack initiation and propagation leading to fracture were simulated using the extended finite element method (XFEM). Two scenarios were compared: one with a protective K-wire and one without. Characterization tests were performed to obtain the necessary mechanical properties.</p> Results <p>The model was validated against data from previous mechanical experiments. The results showed that, while the protective K-wire had minimal effect on the location or onset of crack initiation, it increased the hinge stiffness and stabilized crack propagation. Compared to the configuration without the wire, the K-wire reduced the severity of unstable crack growth, thereby limiting abrupt failure.</p> Conclusions <p>The use of a protective K-wire improves the mechanical stability of the medial hinge by moderating crack propagation without affecting the initiation threshold. This study highlights the importance of modeling crack propagation and not only initiation when evaluating fracture risk in DFO. The findings support the potential clinical benefit of K-wire insertion for preventing hinge-related complications.</p>