**5. Conclusions**

In this study the most common definitions for patello-femoral rotations and the most important conversions between them were described. Using kinematic data of a validated squat motion based on motion capture, it was shown that the angles describing the patellar kinematics are highly dependent on the underlying convention.

If researchers are not aware of the described deviations, misinterpretation of results is very likely, which is critical for clinically relevant studies. Additionally, the comparison of different studies should only be executed if equivalence of the used conventions can be ensured or if the data are carefully transformed. Therefore, the methods from this study will help to uncover the complex relationship between patellar kinematics and anterior knee pain.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/ma14247644/s1, S1: Matlab-template to transform patellar rotations between the described conventions, S2: Instructions for use of the template (S1), S3: Dataset used in this paper in XYZ-Cardan sequence form, S4: Proof for the conversion formulas (1)–(3).

**Author Contributions:** Conceptualization, A.S., M.K., A.M., W.M.M. and T.M.G.; methodology, A.S. and M.K.; software, A.S.; validation, A.S. and M.K.; formal analysis, A.S.; investigation, A.S. and M.K.; resources, A.S., M.K., A.M. and T.M.G.; data curation, A.S. and M.K.; writing—original draft

preparation, A.S.; writing—review and editing, A.S., M.K., A.M., W.M.M. and T.M.G.; visualization, A.S. and M.K.; supervision, A.M. and T.M.G.; project administration, A.S., A.M. and T.M.G.; funding acquisition, A.M. and T.M.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** Three of the authors (A.S., A.M., T.M.G.) were funded by B.Braun Aesculap AG, Tuttlingen, Germany. The funder provided support in the form of salaries for authors A.S., A.M. and T.M.G. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The dataset used for this study is available as Supplementary Material (S3).

**Conflicts of Interest:** Three of the authors (A.S., A.M., T.M.G.) are employees of B.Braun Aesculap AG, Tuttlingen, Germany. W.M.M. is a paid consultant at B. Braun Aesculap AG, but did not receive any reimbursement for the current study. M.K. declares no conflicts of interest.
