*Brief Report* **Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty**

**Joaquin Sanchez-Sotelo**

> Division of Shoulder, Elbow Surgery Mayo Clinic Rochester, Rochester, MN 55905, USA; sanchezsotelo.joaquin@mayo.edu

**Abstract:** The history of humeral component design has evolved from prostheses with relatively long stems and limited anatomic head options to a contemporary platform with short stems and stemless implants with shared instrumentation and the ability to provide optimal shoulder reconstruction for both anatomic and reverse configurations. Contemporary humeral components aim to preserve the bone, but they are potentially subject to malalignment. Modern components are expected to favorably load the humerus and minimize adverse bone reactions. Although there will likely continue to be further refinements in humeral component design, the next frontiers in primary shoulder arthroplasty will revolve around designing an optimal plan, including adequate soft tissue tension and providing computer-assisted tools for the accurate execution of the preoperative plan in the operating room.

**Keywords:** shoulder; arthroplasty; anatomic arthroplasty; reverse arthroplasty

The design of the humeral component in shoulder arthroplasty has evolved tremendously over the last two decades. When discussing the general principles of shoulder replacement, glenoid reconstruction is reviewed frequently. Interestingly, the humeral side of the joint is discussed less often. The purpose of this review article is to provide an update on the principles driving contemporary humeral component design.

#### **1. Brief Historical Perspective**

The history of humeral component design has evolved over a few important milestones that have had a major impact on where we are today.

#### *1.1. From Monoblock and Cemented to Modular Cementless*

Neer is considered by some to be the father of modern shoulder surgery in North America [1]. The original Neer prosthesis was a smooth monoblock hemiarthroplasty with a narrow stem and three sizes. Because the stem was narrow and designed for a cemented application, it could be "floated" in the canal in whichever location was best to position the prosthetic humeral head anatomically [2]. Although early on the original Neer prosthesis was implanted without cement, in the absence of surface treatment, cementless implantation led to a high rate of radiographic loosening [3]. The development of technology to treat the stem with ingrowth-friendly surfaces led to the successful survival of cementless humeral components [4]. At the same time, modular anatomic humeral heads were introduced to allow a humeral head size selection independent of the stem size selection [5]. Currently, most surgeons agree on trying to avoid the use of cement for humeral component fixation at the time of primary arthroplasty; If component revision becomes necessary, cement removal could substantially increase the difficulties associated with the revision procedure.

#### *1.2. A More Sophisticated Understanding of Humeral Geometry*

Traditional cementless ingrowth stems with standard modular heads were noted as not allowing for the anatomic restoration of the proximal humerus geometry in many shoulders: the fit of the stem in the humeral canal dictated where the head would "land".

**Citation:** Sanchez-Sotelo, J. Current Concepts in Humeral Component Design for Anatomic and Reverse Shoulder Arthroplasty. *J. Clin. Med.* **2021**, *10*, 5151. https://doi.org/ 10.3390/jcm10215151

Academic Editor: Markus Scheibel

Received: 7 September 2021 Accepted: 18 October 2021 Published: 2 November 2021

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This prompted studies on the variability of proximal humerus morphology [6] and on the design of implants with various features to adjust the position of the prosthetic head relative to the stem in terms of inclination, eccentricity, and offset [7].
