**5. Conclusions**

Overall, the presented data of the pilot study are biomechanically plausible and in accordance with prior findings of studies analyzing residual limb movement within the sockets of individual with transtibial amputation during gait [4,9,10]. Compared to other measuring approaches [4,11,13], the presented measuring system has an additional value as it enables the analysis of relative motion at a number of specific measuring sites, thus facilitating the detection of compliant soft tissue behavior.

Being tethered constrains the area of use of the system; there is potential for removing this impediment by switching to either wireless data transmission or on-board data storage. Nevertheless, even in its current state, the presented measuring system facilitates the analysis of relative movement between residual limb and prosthetic socket at specific measurement sites for different dynamic

gait situations. Future studies will include the exploration and analysis of different gait situations, socket manipulations, as well as prosthetic components and their impact on relative motion. Additionally, the distribution of relative motion with respect to problematic and unproblematic areas will be investigated.

**Author Contributions:** Conceptualization, V.N. and S.W.; Data curation, V.N. and S.W.; Formal analysis, V.N. and S.W.; Investigation, V.N. and S.W.; Methodology, V.N.; Resources, P.B. and S.R.; Software, V.N. and S.W.; Supervision, P.B. and S.R.; Validation, V.N. and S.W.; Visualization, V.N.; Writing—original draft, V.N. and S.W.; and Writing—review and editing, V.N., S.W., P.B., and S.R.

**Funding:** This research received no external funding.

**Acknowledgments:** We acknowledge support by the German Research Foundation and the Open Access Publishing Fund of Technische Universität Darmstadt. The authors would like to thank the Institute of Production Management, Technology and Machine Tools of the Technische Universität Darmstadt for providing the test rig, the Institute for Production Engineering and Forming Machines of the Technische Universität Darmstadt for the digitization of the plaster model, Össur Deutschland GmbH for providing the liner, and the volunteer as well as the prosthetist Martin Brehm of Sanitätshaus Klein whose participation and support enabled the pilot study.

**Conflicts of Interest:** The authors declare no conflict of interest.
