Inertial measurement units (IMUs) are increasingly being used to assess knee function. The aim of the study was to record patients’ activity levels and to detect new parameters for knee function in the early postoperative phase after TKA. Twenty patients (n = 20) were prospectively enrolled. Two sensors were attached to the affected leg. The data were recorded from the first day after TKA until discharge. Algorithms were developed for detecting steps, range of motion, horizontal, sitting and standing postures, as well as physical therapy. The mean number of steps increased from day 1 to discharge from 117.4 (SD ± 110.5) to 858.7 (SD ± 320.1), respectively. Patients’ percentage of immobilization during daytime (6 a.m. to 8 p.m.) was 91.2% on day one and still 69.9% on the last day. Patients received daily continuous passive motion therapy (CPM) for a mean of 36.4 min (SD ± 8.2). The mean angular velocity at day 1 was 12.2 degrees per second (SD ± 4.4) and increased to 28.7 (SD ± 16.4) at discharge. This study shows that IMUs monitor patients’ activity postoperatively well, and a wide range of interindividual motion patterns was observed. These sensors may allow the adjustment of physical exercise programs according to the patient’s individual needs.

Background: Compliance with rehabilitative physiotherapeutic measures leads to an improvement in outcomes in patients suffering from a variety of musculoskeletal conditions. To date, a tool for assessing the parameters that lead to non-adherence to physical therapy does not exist in the German language. The objective of this paper is to cross-culturally adapt a non-compliance questionnaire to German. Methods: In reference to the “Guidelines for the Process of Cross-Cultural Adaption of Self-Reported Measures”, the questionnaire was translated into German followed by a back-translation into the original language. An expert committee met and refined the pre-final version. A preliminary version was handed out to patients for evaluation of the quality of the resulting German version. Results: After the forward- and back-translation of the questionnaire, some discrepancies were discovered between the translators on the one hand and between the back-translations and the original document on the other. The statistical analysis showed satisfactory results regarding the quality of the questionnaire. Conclusion: The translation and adaption of the items proved to have a high degree of reliability. The German version will be made available for German-speaking researchers and used for evaluating a mobile-application-based physical therapy regimen by the authors of the paper.