**1. Introduction**

Proximal humeral fractures in elderly patients are a common indication for shoulder arthroplasty. Treatment options mainly involve hemiarthroplasty (HA) and reverse shoulder arthroplasty (RSA). Choosing the appropriate treatment option is influenced by many factors, such as the fracture pattern, tuberosity involvement, bone quality, surgeon preference, and the age and activity level of the patient [1].

HA is a well-known procedure for managing proximal humeral fractures. However, with the advent of RSA, the use of HA has become debatable owing to its unpredictable and non-homogeneous outcomes, its technical difficulties, and the fact that it is rarely indicated [2]. Moreover, HA is associated with a high rate of tuberosity complications (up to 50%) [2].

Failure of HA has been attributed to several causes including pain, deep infection, impaired shoulder function, rotator cuff degeneration, cartilage wear of the glenoid, aseptic loosening of the humeral component, and implant instability or dislocation [3,4]. Failed HA may be revised in several ways. Typical treatment options include revision to conventional total shoulder arthroplasty, revision to RSA, and resection arthroplasty [5–9]. Revision to

**Citation:** Reuther, F.; Irlenbusch, U.; Kääb, M.J.; Kohut, G. Conversion of Hemiarthroplasty to Reverse Shoulder Arthroplasty with Humeral Stem Retention. *J. Clin. Med.* **2022**, *11*, 834. https://doi.org/10.3390/ jcm11030834

Academic Editors: Markus Scheibel, Alexandre Lädermann, Laurent Audigé and Luc Favard

Received: 22 November 2021 Accepted: 28 January 2022 Published: 4 February 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/).

RSA may be carried out by exchanging the complete hemiprosthesis (traditional revision RSA) or by retaining the existing humeral stem (conversion RSA). Indicated primarily for concomitant rotator cuff dysfunction, revision to RSA improves shoulder function and relieves pain; however, it is associated with a high complication rate [6,7,9–11].

The removal of the humeral stem is associated with a relatively high risk of humeral shaft fracture, which may jeopardize the anchoring of the new stem and result in implant failure [11–13]. Furthermore, removal of a well-fixed stem can be technically difficult, especially in cases where there is poor bone quality, and may require osteotomy of the humeral shaft [10,11,14]. Levy et al. observed that the high rate (32%) of prosthesisrelated complications in their study of traditional revision RSA with stem exchange for failed HA was mainly associated with bone loss in the proximal humerus, glenoid, or both [7]. Therefore, to prevent bone loss and reduce the risk of intra- and postoperative complications, it would be best to retain the hemiprosthesis stem [10,14,15].

With the advent of modular convertible shoulder prosthesis systems, retaining the humeral stem during revision of HA to RSA has become a viable option. Indeed, the authors of some studies have shown encouraging results accompanied by reduced rates of complications and implant failures [13–18]. Moreover, clinical data have suggested that minimal changes in height and offset [14], shorter operating times [11,13,15], fewer intraoperative complications [11,13,15], and fewer subsequent revision surgeries [10,11,15] are associated with conversion RSA with modular prostheses compared to traditional revision RSA with stem exchange. However, these data are limited to a few short- and mid-term studies, primarily because revision of HA to RSA is a rare indication.

Our aim with this study is to provide further insight into the outcomes of this rare procedure by reporting the mid-term clinical results of an ongoing case series on conversion RSA with a modular prosthesis system in patients revised for failed HA after a proximal humeral fracture.

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

#### *2.1. Study Design and Patient Selection*

This study was a subgroup analysis of an ongoing, multicenter, prospective cohort study of 519 patients with various indications and operated with an Affinis Inverse or Affinis Facture Inverse system (Mathys Ltd., Bettlach, Switzerland) between 6 May 2008 and 1 June 2015. Of these, 17 patients met the following inclusion criteria: revision required for failed HA after proximal humeral fracture, Affinis Fracture or Articula system (Mathys Ltd., Bettlach, Switzerland) implanted as primary prosthesis, and stem removal not required during revision. Reasons for revision included secondary tuberosity dislocation or malunion after primary arthroplasty, luxation or instability after primary arthroplasty, rotator cuff disorder after primary arthroplasty, and glenoid erosion after HA, all resulting in pain and/or loss of function.

Conversion RSA was considered in patients who showed no stem loosening or infection and had adequate soft tissue tension for humeral stem retention, as assessed intraoperatively. Thirteen patients, enrolled from four centers in Germany and Switzerland, were considered suitable for conversion RSA (Figure 1). Of these patients, two were lost due to early revision, two to dementia or old age, and one to dislocation, leaving eight patients at the final follow-up. In the remaining four patients, conversion was not possible due to overstuffing; these patients were treated with traditional revision RSA with stem exchange.

**Figure 1.** Flow diagram of the patient selection.

Patients underwent a clinical examination preoperatively, after one year, and at the final follow-up. The mean final follow-up period was 55.1 months (range: 12.0 to 91.1 months).
