Modified fixations for distal femur fractures following total knee arthroplasty: a biomechanical and clinical relevance study

Abstract Purpose Distal femur fractures adjacent to total knee arthroplasty are a rare yet complex problem. Recently, extramedullary locking plate and retrograde intramedullary nail fixations have become popular options, but the complication rates associated with these procedures are 15–20 %. Modified fixations were assessed in an effort to reduce complications from unstable periprosthetic fractures. Methods Using experimental and finite element methods, this study compared the construct behaviours of a locking plate, a retrograde intramedullary nail, and their modifications (a spiral‐blade supplemented in an intramedullary nail or a locking plate/allograft hybrid) when subjected to various fracture types, locations, loading conditions, and bony strength. The implanted models were used to assess construct stiffness, fracture micromotion, and implant stress under different osteoporotic conditions. Finally, we collected 40 cases for radiological analysis to indicate the appropriate procedure for treating periprosthetic fractures following total knee arthroplasty. Results Regardless of the fracture type, femoral constructs fixed with a conventional or spiral‐blade supplemented intramedullary nail exhibited higher axial but lower torsional stiffness than those fixed with a locking plate. Torsional deformation occurred if the lower‐positioned fracture had no medial support. The locking plate/allograft construct exhibited the highest stiffness and the least micromotion. A review of 40 clinical cases confirmed the above findings regarding the locking plate/allograft construct. Conclusion The spiral‐blade supplement of retrograde intramedullary nail and locking plate/allograft modified constructs significantly stabilizes the unstable fractured gaps. The locking plate/allograft is recommended for the periprosthetic fractures with deficient bone stock and severe osteoporosis to improve alignment and healing potentials.