**1. Introduction**

Over the past decades, the total number of implanted TSAs has increased significantly, and this trend continues [1,2]. Despite a huge overhand of reverse total shoulder implants (RSA), the main indication for aTSA is indicated in patients with primary osteoarthritis (OA) with an intact rotator cuff (RTC) and no severe glenoid retroversion, biconcavity, or bone defect and younger age [3]. In this patient group, aTSA was still the implant of choice.

Longevity and low complication rates are crucial for patients, especially younger individuals. For aTSA survival, the glenoid component represents the weak link [4–6]. There are two types of glenoid components: cemented all-polyethylene glenoids (PEGs) and MBGs.

The usual pick for aTSA is the cemented all-PEG. However, high rates of glenoid component loosening and wear are reported in cemented all-PEGs [6]. The first attempts to improve the stability of glenoid components have led to the development of metal-backed

**Citation:** Noschajew, E.; Rittenschober, F.; Kindermann, H.; Ortmaier, R. Clinical and Radiologic Outcomes after Anatomical Total Shoulder Replacement Using a Modular Metal-Backed Glenoid after a Mean Follow-Up of 5.7 Years. *J. Clin. Med.* **2022**, *11*, 6107. https:// doi.org/10.3390/jcm11206107

Academic Editors: Markus Scheibel, Alexandre Lädermann, Laurent Audigé and Antonio Barile

Received: 4 August 2022 Accepted: 14 October 2022 Published: 17 October 2022

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**Copyright:** © 2022 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/).

<sup>2</sup> Department of Marketing and Electronic Business, University of Applied Sciences Upper Austria, Campus 4400 Steyr, 4600 Wels, Austria

implants. As a rule, MBG components consist of the "metal back" itself and a polyethylene (PE) component that articulates with the humeral head component. This creates a further contact surface between two different materials with possible complications, e.g., dissociation of the two parts or abrasion of the components. Additionally, these glenoids can increase the width of the two components or reduce the PE content and may stress shield the underlying bone due to primary stable fixation [7]. The results of historical metalback glenoids in the literature are rather poor, and based on a systematic review of Papadonikolakis and Matsen carried out in 2014, it was determined that MBGs are not advisable as they have higher failure rates [6]. Following the success of reverse prostheses, the development of modular MBG implants is currently attracting renewed interest. These implants have the potential to be used for both anatomical and reverse shoulder endoprostheses. Revision surgery should theoretically be less complicated as the glenoid baseplate does not require removal [8]. The purpose is thus to lower glenoid component loosening rates and raise the possibility of revising the implant via RSA due to the modularity of most implants. Despite concerning reports of high complication rates of MBGs in aTSA, newer designs promise to lower the complication rate and yield better results with the possibility of converting the prosthesis very easily to a reverse implant if necessary [8]. In this study, we evaluated the clinical and radiological results, as well as the survival rate of the aTSA with a modular cementless flat MBG.

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