4 Evolution of Humeral Component Technology in Reverse Shoulder Arthroplasty

10.1055/b-0037-146565

4 Evolution of Humeral Component Technology in Reverse Shoulder Arthroplasty

Andrew T. Assenmacher, Eduard Alentorn-Geli, and John W. Sperling

Abstract

The humeral component is an essential part of creating a well-functioning reverse shoulder implant; however, it is often overlooked. The majority of literature and changes in reverse shoulder arthroplasty (RSA) have focused on the glenoid component. The humeral component has continued to evolve with greater understanding of glenohumeral biomechanics and fixation techniques. Some of these changes have advanced with advances in anatomic total shoulder arthroplasty and lower extremity arthroplasty. Fixation techniques have changed over time from the original Grammont prosthesis, which was all cemented to press-fit designs that have gained popularity as fixation techniques continue to improve and show good results with similar low rates of loosening to cemented implants. Regional variations exist in the acceptance of press-fit techniques, however. As we better understand the differences in bio-mechanics of the RSA as a nonanatomic device, we also improve our ability to optimize functional ability of the patient by positioning the humeral component to maximize moment arms of the musculature and avoiding mechanical impingement. Another goal is to achieve a long-lasting implant, as the revision setting in shoulder arthroplasty can be very difficult in regard to technique and complications. As long-term literature becomes available, new generations of humeral implants should continue to advance and improve upon these principles of optimizing fixation and function.

4.1 Introduction

Although the majority of literature and design changes in reverse shoulder arthroplasty (RSA) have focused on changes regarding the glenoid and baseplate loosening, modifications in the humeral side are important to maximize function and fixation and decrease complication. The first stem designed for shoulder replacement was in 1893 by Dr. Jules Émile Péan, based on an 1890 design by Dr. Thermistocles Gluck, made of platinum and leather. ¹ The first anatomic total shoulder arthroplasty (TSA) by Dr. Charles Neer was a nonconstrained implant with a humeral component made of vitallium. ²

Multiple designs were attempted to compensate for severe rotator cuff deficiency, using various glenosphere modifications and fixation configurations (► Fig. 4.1). All designs resulted in failure at the glenoid component. ³ Paul Grammont’s reverse articulated design shifted center of rotation medially and distally (► Fig. 4.2). ⁴ These forces pass through the fixed center of rotation and transform the shearing torque associated with previous failures into compressive forces at the glenoid–bone interface. Grammont’s original humeral stem was trumpet-shaped inverted polyethylene stem that was cemented in (► Fig. 4.3). This was modified to become the first Food and Drug Administration (FDA)-approved RSA prosthesis (► Fig. 4.4), the Delta III (DePuy, Warsaw, IN). This stem was a conical monobloc humeral stem with either a polished or hydroxyapatite coated for cemented or uncemented use, respectively. Design modifications have continued in order to improve both fixation and function of the prosthesis.

**Fig. 4.1** The Kessel prosthesis. Early constrained design with all polyethylene humeral component. Results reported between 1982 and 1985 showed a high incidence of glenoid loosening due to the constrained design and was abandoned. (Reproduced with permission from Brostrom LA, Wallensten R, Olsson E, Anderson D. The Kessel prosthesis in total shoulder arthroplasty: a five-year experience. Clin Orthop Relat Res 1992;(277):155–160.)

**Fig. 4.2** An original diagram from Paul Grammont of his design of a “medializing” prosthesis with two-part humeral component. The humeral stem and neck were intended to be a rotating system, which was later abandoned. (Reproduced with permission from Baulot E, Sirveaux F, Boileau P. Grammont’s idea: the story of Paul Grammont’s functional surgery concept and the development of the reverse principle. Clin Orthop Relat Res 2011;469(9):2425–2431.)

**Fig. 4.3** The “Trompette” reverse prototype was one of the early Grammont designs. It used a polyethylene humeral component and was first implanted in 1986. (Reproduced with permission from Baulot E, Sirveaux F, Boileau P. Grammont’s idea: the story of Paul Grammont’s functional surgery concept and the development of the reverse principle. Clinical Orthop Relat Res 2011;469(9):2425–2431.)

**Fig. 4.4** The first FDA-approved design was the Grammont Delta III prosthesis (Depuy). This five-part design included metaglenoid (baseplate), glenosphere, polyethylene cup, humeral neck, and humeral stem. Humeral component was designed for cementation. (Reproduced with permission from Boileau P, Watkinson DJ, Hatzidakis AM, Balg F. ⁹ )

4.2 Modern Designs

Many of the humeral component changes in RSA are originated in TSA evolution. In TSA design, the first-generation humeral stems were monobloc. Modularity was introduced into the second-generation stems, and variations in offset and inclination were introduced in third-generation stems. The latest generation may be in situ adjustable. Modern designs generally use cobalt-chrome (Co-Cr) for cemented technique and titanium (Ti-6Al-4V) for press-fit fixation with hydroxyapatite coating. Co-Cr is generally polished for cementation purposes. Different strategies have been implemented for augmentation of stems to enhance uncemented fixation. Coating is used as an adjunct to most press-fit devices. Roughening, grit-blasting, plasma spray, and hydroxyapatite coatings have all been used to promote ongrowth fixation. Ingrowth with porous scaffolds has also been used to increase fixation. Antirotational strategies include proximal fins or distal flutes/grooves in some stems. The original Grammont’s design contained a screw mechanism to attach the stem components but was replaced with Morse taper due to loosening. ³ The Morse taper is now generally used in all arthroplasty designs. Some shoulder implants have utilized double Morse tapered designs and offset Morse taper designs.

The next generation of implants is currently using strategies to attempt to improve complications associated in revision and long-term complications of polyethylene wear. The use of convertible systems decreases the risk of complications associated with implant removal and revision, such as bone and soft-tissue loss, fracture, and neurovascular injury. These convertible systems allow for the humeral stem to remain in place and exchange of the humeral ball for a tray. The optimum position for TSA, however, may not be optimal for RSA. A stem that does not allow proper positioning and tensioning after conversion should not be retained, and the stem should be revised accordingly. Shoulder arthroplasty designs have historically borrowed from lower extremity joint literature. The addition of vitamin E to the polyethylene is currently under research to decrease polyethylene wear. Another strategy is use of inverted systems where the polyethylene and metal portions of the joint are reversed. Inverted systems, currently the SMR HP prosthesis (Lima LTO, Italy) and Affinis Inverse Shoulder System (Mathys Ltd Bettlach, Switzerland), use a polyethylene glenosphere and Co-Cr or ceramic liner to attempt to reduce polyethylene wear and notching. Currently, these designs are not available in the United States. These newer strategies have yet to be studied in depth in the shoulder literature. Modularity in reverse allows adjustment of features such as in thickness of the tray and insert, adjusting of offset, and increasing constraint.

4.3 Current Implants

A list of current reverse shoulder systems is found in ► Table 4.1.

**Table 4.1** List of current reverse arthroplasty systems
Current reverse shoulder systems	Company	Inclination/neck-shaft angle (degrees)
Aequalis II Reverse Shoulder Systema	Tornier, Amsterdam, the Netherlands	35/145
Affinis Inverse Shoulder Systemb	Mathys Ltd Bettlach, Switzerland	25/155
AltiVate Reverse	DJO Surgical, Austin, TX	45/135
Arrow Anatomical Shoulder Systema	FH Orthopedics, Heimsbrunn, France	45/135
Anatomical Inverse-Reverse Shoulder Systema	Zimmer, Warsaw, IN	45/135 (25/155 with tray)
Bio-Modular Shoulder Systema	Biomet, Warsaw, IN	55/125 (45/135 with tray)
Comprehensive Reverse Shoulder System	Biomet, Warsaw, IN	45/135 (33/147 with liner)
Delta Xtend Reverse Shoulder	Depuy-Synthes, Warsaw, IN	25/155
Equinoxe Reverse Systema	Exactech, Gainesville, FL	35/145 (in-situ adjustability)
Promos Modular Shoulder System	Smith & Nephew, London, UK	25/155
RSP—Reverse Shoulder Prosthesis	DJO Surgical, Austin, TX	45/135
SMR (Systema Multiplana Randelli) and SMR HP prosthesisb	Lima LTO, Italy	45/135
Titan Reverse Shoulder Systema	Integra Lifesciences, Plainsboro, NJ	38/142
Trabecular Metal Reverse System (TMRS)	Zimmer, Warsaw, IN	30/150
Univers Revers	Arthrex, Naples, FL	25/155 or 45/135
Vaios Inverse Shoulder Replacement Systema	JRI Orthopaedics, Sheffield, UK	30/150
^a Convertible systems.
^b Not available in United States. Inverted system option.