**1. Introduction**

Proximal humeral fractures are common fractures in the elderly and affecting up to 111 per 100,000 persons per year [1]. In displaced three- or four-part fractures, open reduction and internal fixation (ORIF) aims at the best possible restoration of shoulder anatomy and thus shoulder function [2–4]. Shoulder function after ORIF mainly improves between 3 and 12 months after surgery but acute loss of reduction usually happens within 6 weeks after surgery [5–8]. In addition to other factors such as the donor's age and sex, bone stock quality, complexity and reduction quality of the fracture, comorbidities, fixation type and augmentation, the rehabilitation protocol may contribute to these early failures [9–18]. There are differences in rehabilitation programs after ORIF whereas some surgeons stimulate an immediate functional non-weight bearing rehabilitation program, while others have a less aggressive approach and prefer an initial physiotherapist assisted rehabilitation program [19]. It remains unclear what impact these different rehabilitation programs have on postoperative patient satisfaction, return to function, complications and failures [20].

**Citation:** Herteleer, M.; Runer, A.; Remppis, M.; Brouwers, J.; Schneider, F.; Panagiotopoulou, V.C.; Grimm, B.; Hengg, C.; Arora, R.; Nijs, S.; et al. Continuous Shoulder Activity Tracking after Open Reduction and Internal Fixation of Proximal Humerus Fractures. *Bioengineering* **2023**, *10*, 128. https://doi.org/ 10.3390/bioengineering10020128

Academic Editors: Christina Zong-Hao Ma, Zhengrong Li and Chen He

Received: 21 December 2022 Revised: 6 January 2023 Accepted: 8 January 2023 Published: 18 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Moreover, it remains challenging to capture the frequency and extent of shoulder activity performed by a patient throughout the day. Technological advancements allow recording patient activity via trackers and motion capture sensors, allowing continuous assessment of activities of daily life for periods ranging from a few days up to several weeks [21,22].

The goal of this pilot study was threefold. The first aim was to evaluate the feasibility of continuously monitoring shoulder activity over a period of several weeks. The second aim was to describe the evolution of shoulder activity within the first six postoperative weeks in proximal humerus fracture patients treated with locked plate osteosynthesis. The third aim was to evaluate potential differences in the degree of postoperative shoulder activity between two different rehabilitation protocols.

#### **2. Materials and Methods**

This multi-centric prospective study investigated shoulder activity with accelerometerbased trackers during the first six postoperative weeks in elderly patients with a complex proximal humerus fracture treated with the PHILOS plate (DePuy Synthes, Zuchwil, Switzerland). The two study centers were the University Hospitals Leuven and Medical University Innsbruck. Note that the study sites will be referred to in an anonymized manner below. The study was approved by the local ethical committees (approval numbers S62376 and 1281/2018, respectively).
