The role of complex clinical scenarios in the failure of modular components following revision total knee arthroplasty: A finite element study. 
Modular prostheses are increasingly applied in complex revision knee arthroplasty scenarios due to the greater intraoperative flexibility they provide to the surgeon, for example, accurate placement of stem in canal while maintaining a good fit distally for complex femoral geometry.  However, growing evidence indicates that these modular devices often fail at the stem junction.  Modular prostheses are generally applied to provide enhanced fixation in poor quality bone or in the presence of condylar defects.  From the literature, it is unclear which of these patient scenarios contribute the most to modular component failure.  The present study uses finite element (FE) models to answer this question.  The findings of this study indicate that the most significant increase in stem junction stress occurs in the presence of large condylar defects.  However, taking into account standard clinical practice (large F3 defects typically result in distal femoral replacement), the most significant factor is then found to be compromised bone quality, these findings are particularly evident at higher flexion angles.  Based on the findings of this study, it can be concluded that patients with large femoral defects or severely compromised bone quality are particularly vulnerable to implant failure when a modular approach is adopted.