3.1 Introduction

Reverse shoulder arthroplasty (RSA) has recently gained popularity as a treatment for painful shoulder conditions that arise due to a loss of the stable fulcrum at the glenohumeral articulation. Many surgeons credit Paul Grammont with the development of RSA, and indeed the current designs reflect his contribution to the field of shoulder surgery to this day. In fact, the original designs of RSA were developed between 1970 and 1973 by Charles S. Neer given that his Mark I, Mark II, and Mark III systems featured a fixed fulcrum and reversed geometry of the glenohumeral joint. ¹ Despite promising initial results in terms of motion, Neer quickly abandoned his designs due to fixation failure between the glenosphere and the scapula. From the very beginning, it was clear that successful design of RSA depended on a properly sized glenoid component with secure fixation to the scapula in order to accommodate the increased stress on such a constrained implant.

3.2 Early Designs

When Neer introduced his Mark I design in the early 1970s, a very large glenosphere was used to allow for maximum rotational motion at the glenohumeral articulation. Unlike modern designs that were influenced by Grammont, Neer’s design featured a full sphere, rather than a hemisphere. The trade-off in this case, was that the subscapularis tendon could not be reattached, and both rotational motion and stability suffered as a result. The Mark II featured a smaller glenosphere, but the diminished excursion of the prosthesis and limited range of motion were concerning. The Mark III design kept the smaller ball design and incorporated axial rotation into the humeral component to increase range of motion. Despite improvements in range of motion, the Mark III design was ultimately shelved due to catastrophic failures at the glenosphere–scapula interface. In all of the Mark systems, fixation relied upon a keeled design that was secured using acrylic bone cement. Significant improvements in glenosphere design and fixation were clearly needed before RSA could gain widespread acceptance.

The use of uncemented fixation to the scapula debuted early in the design process. In the early 1970s, Gerard and Lannelongue devised a glenoid component that was fixed with screws. ² Another design by Kölbel featured both cement and screw fixation, this time with the screw used to transfix a forked design across the scapular spine. ³ A retaining ring was also used to constrain the sphere to the humerosocket, and only one failure of scapular fixation was noted in 14 patients with 4 to 8 years of follow-up. Later, Kessel and Bayley ⁴ reported on a series of patients in whom a single large self-tapping screw was used to fix the glenosphere to the scapula, and they found no failures due to scapular fixation as well as satisfactory outcomes in 26 of 31 shoulders treated with the Kessel RSA. These designs, and others that emerged in the 1970s and early 1980s, gradually improved the fixation of the glenoid component. However, the primary objective of these designs was constraint, and it was not until the development of the Grammont prosthesis that the benefits of medialization of the glenohumeral COR and securing the sphere to a baseplate would be recognized.

Paul Grammont’s “Trompette” prosthesis was designed in 1985 in order to give the deltoid better mechanical advantage over the glenohumeral articulation in rotator cuff-deficient shoulders. ⁵ Grammont initially used a two-thirds sphere design with attachment to a ceramic baseplate that was cemented to the scapula. Early in the process, he revised his glenosphere design to a hemisphere, which placed the COR at the glenoid surface. He also revised the baseplate to feature uncemented fixation with a porous-coated central peg and two divergent transfixion screws. This would become the Delta III design that debuted in 1991 and continues to influence the modern designs of today (► Table 3.1).

Table 3.1 Description of the existing reverse total shoulder arthroplasty systems in use today

Company	System	Baseplate geometry	Central fixation	Peripheral screws	Number of screws	Glenosphere	Sizes	Humerus	Humerus geometry	Figures
Arthrex	Univers Revers	Oval flat	Tapered post	4.5 mm compression or locking	2	Medial or lateral	36,39,42	135,155	Inlay	(Fig. 3.1)
Aston	Duocentric	Oval convex	Peg	Compression 4.2 mm or 5mm	3	Medial or lateral	36,40	145	Onlay	(Fig. 3.2)
Biomet	Comprehensive	Circular flat	Peg with separate 6.5 mm central screw	4.75 mm compression or locking	4	Medial or lateral	36,41	147	Onlay	(Fig. 3.3)
Depuy Synthes	Delta XTEND	Circular convex	Threaded peg	4.5 mm compression or locking	4	Medial or lateral	38,42	155	Inlay	(Fig. 3.4)
DJO	Reverse Shoulder Prosthesis (RSP)	Circular convex	Integrated 6.5 mm cancellous screw	5mm locking	4	Lateral	32,36,40,44	135	Inlay	(Fig. 3.5)
Euros	Scultra II	Oval flat	Caged peg	4.5 mm or 6.5 mm compression	2	Medial or lateral	36	135		(Fig. 3.6)
Evolutis	UNIC	Oval convex	Helical blade	Compression	4	Medial	34,38	140	Onlay	(Fig. 3.7)
Exactech	Equinoxe	Oval convex + / -augment	Caged peg	Locking	6	Lateral	38,42,46	145	Onlay	(Fig. 3.8)
FH	Arrow	Oval convex	Keel	Compression	2	Lateral	36,39	135	Onlay	(Fig. 3.9)
Innovative Design	Verso	Circular flat	Tapered screw	5mm Compression	6	Lateral	36,41	145	Inlay	(Fig. 3.10)
Integra	Titan	Oval convex	Peg with 5.5 mm cancellous screw	4.5 mm Compression and Locking	4	Lateral	38	142	Inlay	(Fig. 3.11)
Lima	SMR	Oval convex	Threaded peg	6.5 mm Compression	2	Medial	36,40,44	Variable	Inlay	(Fig. 3.12)
Mathys	Affinis	Circular convex	Dual threaded	4.5 mm Compression, 4mm Locking	3	Medial	36,39,42	155	Inlay	(Fig. 3.13)
Tornier	Aquelis Ascend	Circular flat	Threaded post	Locking and compression	4	Medial or lateral	36,42	145	Onlay	(Fig. 3.14)
Zimmer	Reverse	Circular flat	Post	4.5 mm Locking	2	Lateral	36,40	143	Inlay	(Fig. 3.15)