The Swing Angle of the Intramedullary Rod in the Canal During Medial Mobile-bearing Unicompartmental Knee Arthroplasty: a Finite Element Analysis Study

Abstract Background: To determine the swing angle of the intramedullary rod in the canal during medial mobile-bearing unicompartmental knee arthroplasty (UKA), we simulated the intramedullary localization process of mobile-bearing UKA via digital technology and analyzed the swing angle of the intramedullary rod swing in the canal through finite element analysis. Methods: Patients requiring mobile-bearing UKA in our department were prospectively selected. A three-dimensional femur model was established, and intramedullary rods of different lengths were inserted. The swing of the intramedullary rod in the canal was simulated, the angle of the moving rod was obtained, and the anatomic parameters of the femur were measured. Parson's correlation between the swing angle of the intramedullary rod and anatomical parameters of the femur were analyzed. Results: The longer the intramedullary rod, the smaller the swing range; this difference was statistically significant (P<0.05). The maximum swing range of the same intramedullary rod was significantly larger in the sagittal than in the coronal plane (P<0.05). Parson’s correlation analysis indicated that the isthmic diameter and femur length significantly correlated with the 20-cm and 25-cm and 30-cm rod swing ranges, respectively.Conclusion: We proved that the longer the intramedullary rod, the smaller the swing angle in the femoral medullary canal. The femoral medullary canal diameter and femur length affect the swing angle; thus, in patients with a shorter femur length, we recommend 25-cm intramedullary rods.