# Different ISO Standards' Wear Kinematic Profiles Change the TKA Inlay Load  
[PERSON]  
Department of Orthopedic Surgery, Physical Medicine and Rehabilitation, Campus Grosshadem, University Hospital of Munich (LMU), Marchionistr.  
component. The force-controlled norm induces this movement with a load profile on the components, and the displacement-controlled standard therefore uses fixed translational and rotational values. Interestingly, for the displacement standard, the anterior/posterior movement of the tibia and the rotational profile were changed in 2014 to the opposite way around because [PERSON] et al. showed that the load-controlled standard was not consistent with the displacement-controlled standard in human specimens [5].  
Various working groups have been working on similar issues. [PERSON] et al. compared the DC norm of 2004 with the changed one of 2014 [6]. By means of computer simulation, the kinematic inputs, contact condition, and wear of both standards were investigated. They showed a lower wear rate for the newer version, but at the same time a higher wear area. Overall, they were able to show a difference between the two standards and advised that historical wear results be compared with newer results only with caution [6]. In another study, the ISO standard 14342-1 was compared with American Society for Testing and Materials (ASTM) F3141. They found a very similar overall wear rate (13.64-54.9 mm\({}^{3}\)/million vs. 13.48-55.26 mm\({}^{3}\)/million) but different wear contours and wear depth [7].  
These differences in wear may result in problems for medical companies. For example, for the approval of a new medical device, the new European Medical Device Regulation (MDR) or American Food and Drug Administration (FDA) provides the possibility of using clinical data related to an equivalent device, sometimes called a \"predicate device\", in the clinical evaluation process. For the MDR, this is only possible if the technical, biological, and clinical characteristics are equivalent; therefore, full access to the technical documentation of the medical device is needed, which will lead in many cases to a situation where results may only be compared within inhouse products. However, if the differences in the load and motion profiles across different ISO standard versions are too great, and knowing that these kinematic profiles and loads strongly influence the generation of wear, comparisons will be difficult [8]. This leads to problems in the certification process of new implants, because if experimental wear tests are no longer comparable due to major changes over the years, companies lose the possibility of comparing results to their old result database.  
The aim of this study was therefore to compare the different ISO standards across different publication years and loading concepts and to gain a deeper insight into the resulting kinematics and differences in stress in the polyethylene insert. To discover whether low congruence inlay designs are more affected by different loading conditions, the differences in inlay design across the standards should be analysed.  
We hypothesise that (1) each norm will result in different inlay stresses (three norms tested: ISO 14243-1:2002, ISO 14243-1:2009, and ISO 14243-3:2014) within the same inlay design, and (2) the force-controlled norm will differ in stress and kinematics between 2002 and 2009. The comparison of the kinematics and the stress behaviour is investigated using finite element methods.