The role of cemented and press-fit stem extension in repair tibial bone defect in revision total knee arthroplasty - a finite element analysis

Introduction: Stem extension is commonly used in revision total knee arthroplasty to enhance stability when bone defect is encountered. The present study was conducted to compare the load sharing characteristics and construct stability of the tibial component when using cemented and cementless press-fit stem extensions. Methods: A total of 3 finite element models simulating 5, 7.5, 10, 12.5 and 15 mm height wedge-shaped bone defect in the medial side of tibia plateau were constructed. All defects were repaired by cement with 2 screws reinforcement. Tibial standard implant without long stem, and 45, 60, 75, 90, 115 mm cemented and press-fit stems were simulated. The micromotion between the bone-cement interface was investigated. Results: In all defect models, both cemented and press-fit long stems had greater reduction in the bone-cement interface micromotion than the standard implant. Cemented stems transferred more applied load to diaphyseal bone than the pressfit stem. Cemented stems showed relative lower interface displacement than press-fit stems in all models. When the defect was 12.5 mm, stems longer than 45 mm were required. When the defect was 15 mm, the stems longer than 60 mm were required. Discussion and Conclusion: The use of intramedullary stems aid to supply the initial support for revision implants providing load sharing and increase component stability. Strategy of using different lengths of stems is based on the size of defects