**1. Introduction**

With the baby boomer generation reaching 65 years of age, the socioeconomic issues of an aging population, with higher incidences of degenerative joint diseases [1] and fractures, will certainly affect inpatient care. While the increase in the number of hip and knee arthroplasties is predicted to slow down over the next decades [2–7], only a few studies have examined national trends for upper extremity arthroplasties [8,9]. However, in contrast to hip and knee arthroplasty, the demand and impact of shoulder arthroplasty have been underestimated in the past, probably due to a smaller number of arthroplasties performed per year. In the United States, which is commonly used as a reference in other orthopedic studies, current growth rates for shoulder arthroplasties are reported to be comparable with, or even higher than the growth rates for total hip and knee procedures [8,10]. Furthermore, the projected demand for shoulder arthroplasty is

**Citation:** Klug, A.; Herrmann, E.; Fischer, S.; Hoffmann, R.; Gramlich, Y. Projections of Primary and Revision Shoulder Arthroplasty until 2040: Facing a Massive Rise in Fracture-Related Procedures. *J. Clin. Med.* **2021**, *10*, 5123. https:// doi.org/10.3390/jcm10215123

Academic Editor: Emmanuel Andrès

Received: 30 September 2021 Accepted: 28 October 2021 Published: 31 October 2021

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anticipated to increase more rapidly over the next decade based on the future demographic development of the U.S. [9]. However, in contrast to the United States, Germany and many other Western (European) countries face population declines in the near future due to lower birth and immigration rates, which are unable to make up for the aging of the population. Based on current projections, many other countries will likely be heading in the same direction within the next few decades [11,12]. As the incidence of shoulder arthroplasty is higher for older patients, an increased burden in the future has to be expected, as agerelated diseases, like osteoarthritis, osteoporosis, frailty-syndrome or injuries are becoming increasingly important. In Germany, the incidence of shoulder arthroplasty is amongs<sup>t</sup> the highest around the world [13], due to a relatively old population and a social healthcare system, which provides almost unlimited access to all parts of orthopedic treatment. However, as the working population is shrinking and increasingly aging, the healthcare system faces the challenge of higher demand and costs.

Furthermore, newer implant designs and expanded indications, such as the use of reverse total shoulder arthroplasty (rTSA) for proximal humerus fractures [14,15], have also led to the rising surgical volume of shoulder arthroplasties in recent years. A shift towards total shoulder arthroplasty (TSA) and away from hemiarthroplasty (HA) procedures have also been reported, presumably because of better outcomes both in degenerative and traumatic conditions [16,17]. However, the contribution of rTSA to future projections of shoulder arthroplasties has not been evaluated yet. Furthermore, the revision burden of these procedures appears to be rising as well [8], which is of particular concern because revision surgery tends to be more complex and cost-intensive than primary arthroplasty [18].

Therefore, the aim of this study was to provide a reliable projection of the future need for primary and revision shoulder arthroplasty to assist orthopedic surgeons, politicians, healthcare providers and other stakeholders (insurances, industry) in providing enough human and financial resources to maintain the current standard of care.

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

#### *2.1. Data Collection*

An analysis of the data from the national inpatient statistics of Germany (DeStatis) was conducted. This database includes all annual inpatient treatment reports from all German hospitals and medical institutions, making this study a nationwide survey (except military and psychiatric facilities). The data are based on the International Statistical Classification of Diseases and Related Health Problems, Tenth Edition (ICD-10) and the German procedure classification system (OPS), which is the official classification system for encoding surgical procedures in Germany. These statistics contain anonymized data sustaining plausibility checks and data validation on a medical and economic level. All cases reported between 2010 and 2019 were analyzed based on the corresponding OPS codes in its most recent version [19], as well as their associated ICD diagnosis. Data after 2019 was intentionally excluded because of the interference due to the COVID-19 pandemic, which led to a massive reorganization of the medical system in 2020 and early 2021. All patients with shoulder arthroplasty, including either anatomic or reverse arthroplasty and all hemiarthroplasties, as well as all revision shoulder arthroplasties and explanations, were identified. During the study period, no coding changes were performed. Age was categorized in the following groups: <55, 55–59, 60–64, 65–69, 70–74, 75–79, 80–84, 85–89, and older than 90 years.

Population data was available from official population projection statistics until 2040 [20]. These population projections consider the future mortality and increased life expectancy for the oldest population groups, and the immigration rate.
