Discrepancies in Sagittal Alignment of the Lower Extremity Among Different Brands of Robotic Total Knee Arthroplasty Systems

Background There is an increasing number of different brands of robotic total knee arthroplasty (TKA) systems. Most robotic TKA systems share the same coronal alignment, while the definitions of sagittal alignment vary. The purpose of this study was to investigate whether these discrepancies impact the sagittal alignment of the lower extremity. Methods A total of seventy-two lower extremity computed tomography (CT) scans were included in our study, and three-dimensional models were obtained using software. A total of seven brands of robotic TKA systems were included in the study. The lower extremity axes were defined based on the surgical guide for each implant. We also set the intramedullary axis as a reference to evaluate the discrepancies in sagittal alignment of each brand of robotic system. Results On the femoral side, the axis definition was the same for all seven robotic TKA systems. The robotic TKA axes showed a 2.41° (1.58°, 3.38°) deviation from the intramedullary axis. On the tibial side, the seven robots had different axis definitions. The tibial mechanical axis of six of the TKA systems was more flexed than that of the intramedullary axis, which means the posterior tibial slope was decreased while the tibial mechanical axis of the remaining system was more extended. Conclusion The sagittal alignment of the lower extremity for seven different brands of robotic TKA systems differed from each other and all deviated from the intramedullary axis. Surgeons should be aware of this discrepancy when using different brands of robotic TKA systems to avoid unexpected sagittal alignment and corresponding adverse clinical outcomes. There is an increasing number of different brands of robotic total knee arthroplasty (TKA) systems. Most robotic TKA systems share the same coronal alignment, while the definitions of sagittal alignment vary. The purpose of this study was to investigate whether these discrepancies impact the sagittal alignment of the lower extremity. A total of seventy-two lower extremity computed tomography (CT) scans were included in our study, and three-dimensional models were obtained using software. A total of seven brands of robotic TKA systems were included in the study. The lower extremity axes were defined based on the surgical guide for each implant. We also set the intramedullary axis as a reference to evaluate the discrepancies in sagittal alignment of each brand of robotic system. On the femoral side, the axis definition was the same for all seven robotic TKA systems. The robotic TKA axes showed a 2.41° (1.58°, 3.38°) deviation from the intramedullary axis. On the tibial side, the seven robots had different axis definitions. The tibial mechanical axis of six of the TKA systems was more flexed than that of the intramedullary axis, which means the posterior tibial slope was decreased while the tibial mechanical axis of the remaining system was more extended. The sagittal alignment of the lower extremity for seven different brands of robotic TKA systems differed from each other and all deviated from the intramedullary axis. Surgeons should be aware of this discrepancy when using different brands of robotic TKA systems to avoid unexpected sagittal alignment and corresponding adverse clinical outcomes.