Abstract
Mechanical and kinematical aligning techniques are the usual positioning methods during total knee arthroplasty. However, alteration of the physiological joint line and unbalanced medio-lateral load distribution are considered disadvantages in the mechanical and kinematical techniques, respectively. The aim of this study was to analyse the influence of the joint line on the strain and stress distributions in an implanted knee and their sensitivity to rotational mal-alignment. Finite element calculations were conducted to analyse the stresses in the PE-Inlay and the mechanical strains at the bone side of the tibia component-tibia bone interface during normal positioning of the components and internal and external mal-rotation of the tibial component. Two designs were included, a horizontal and a physiological implant. The loading conditions are based on internal knee joint loads during walking. A medialization of the stresses on the PE-Inlay was observed in the physiological implant in a normal position, accompanied by higher stresses in the mal-rotated positions. Within the tibia component-tibia bone interface, similar strain distributions were observed in both implant geometries in the normal position. However, a medialization of the strains was observed in the physiological implant in both mal-rotated conditions with greater bone volume affected by higher strains. Although evident changes due to mal-rotation were observed, the stresses do not suggest a local plastic deformation of the PE-Inlay. The strains values within most of the tibia component-tibia bone interface were in the physiological strain zone and no significant bone changes would be expected. The physiological cut on the articular aspect showed no detrimental effect compared to the horizontal implant.
Highlights
Over the last decades, total knee arthroplasty (TKA) has proved to be a successful procedure for the treatment of patients with severe osteoarthritis of the knee joint with survival rates of 95% at 15 years reported [1, 2]
Related to this dissatisfaction is the optimal alignment of the implant components, which remains a matter of debate [4]
Two TKA implants were included, a traditional horizontal implant and an implant with an physiological joint line; both geometries were developed by OHST AG, Rathenow, Germany
Summary
Total knee arthroplasty (TKA) has proved to be a successful procedure for the treatment of patients with severe osteoarthritis of the knee joint with survival rates of 95% at 15 years reported [1, 2]. Around 20% of patients are dissatisfied with the outcome, citing limited function, residual pain and instability as the main reasons [3]. Related to this dissatisfaction is the optimal alignment of the implant components, which remains a matter of debate [4]. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript
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