The optimal size of screw for using cement-screw technique to repair tibial defect in total knee arthroplasty: A finite element analysis.

Cement can be reinforced with cancellous screws for repairing tibial defect in total knee arthroplasty (TKA). However, it is still unknown which size (diameter, length) of screws is better, and the purpose of this study was to perform a finite element analysis (FEA) to determine it. Twelve FEA models were set to represent the cement-screw technique with different diameters (3.5 mm, 5 mm and 6.5 mm) and lengths (20 mm, 25 mm, 30 mm and 35 mm). Contact stresses on the surface of cancellous bone in different areas were calculated. Compared to screws with diameter of 3.5 mm, stresses on the surface of bone defect reduced 5.75% of 5 mm and 10.68% of 6.5 mm for the screw length of 20 mm, 4.23% of 5 mm and 9.16% of 6.5 mm for 25 mm, 6.65% of 5 mm and 12.30% of 6.5 mm for 30 mm, and 5.05% of 5 mm and 12.16% of 6.5 mm for 35 mm. Compared to screws with diameter of 5 mm, stresses on the surface of defect reduced 5.24%, 5.15%, 6.05%, and 7.49% of 6.5 mm for the screw length of 20, 25, 30, and 35 mm. However, it did not show any significant difference in other comparisons. For the treatment of tibial defect in TKA with cement-screw technique, longer screw may not achieve better stability, but the thicker screw can reduce more stresses on the surface of tibial defect and achieve better stability. However, the depth of bone defect must be considered when making a choice.