
==== Front
JSES Int
JSES Int
JSES International
2666-6383
Elsevier

S2666-6383(24)00151-8
10.1016/j.jseint.2024.06.003
Shoulder
Shoulder Arthroplasty
Optimizing stability and motion in reverse shoulder arthroplasty with a 135° neck-shaft-angle: a computer model study of standard versus retentive humeral inserts
Bauer Stefan MD ab
Blakeney William G. MD bc
Lannes Xavier MD Xavier.Lannes@ehc.vd.ch
a∗
Wang Allan W. MD b
Shao Wei MD a
a Centre de l’épaule et du membre supérieur de la Côte, Ensemble Hospitalier de la Côte, Morges, Switzerland
b School of Surgery, University of Western Australia, Perth, WA, Australia
c Department of Orthopaedic Surgery, Royal Perth Hospital, Perth, WA, Australia
∗ Corresponding author: Xavier Lannes, MD, Centre de l’épaule et du membre supérieur de la Côte, Ensemble Hospitalier de la Côte, Chemin du Crêt 2, Morges 1110, Switzerland. Xavier.Lannes@ehc.vd.ch
19 6 2024
9 2024
19 6 2024
8 5 10871094
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Background

There has been a trend to shift from a 155° and 145° neck-shaft-angle (NSA) to a more “anatomical” reverse shoulder arthroplasty with less distalization and a 135° NSA. Multiple studies have shown that a 135° NSA is beneficial for motion. There are some concerns about primary implant stability with a 135° NSA. When instability is detected, increasing the tension with thicker inlays or changing the NSA to 145° are possible solutions. A retentive 135° (Ret135) inlay may be an alternative to avoiding increased distalization; however, retentive liners are widely regarded as salvage options reducing range of motion (ROM) and avoided by most surgeons. The hypothesis of this study was that a retentive 135° insert of the tested implant system may not have drawbacks for impingement-free ROM compared to a standard 145° insert (Sta145).

Methods

In this computer model study, 22 computed tomographic scans (11 males/11 females) were used to create models with a constant humeral stem (Perform/Stryker) and +3 mm lateralized baseplate +36 mm glenosphere for females and +6 mm lateralized baseplate +39 mm glenosphere for males using Blueprint software (Imascap, Brest, France). A Ret135, standard 135° (Sta135), and Sta145 (+10°) insert were compared for adduction (ADD), extension (EXT), external rotation (ER), and internal rotation (IR) all with the arm at the side as well as for combined IR (CIR = EXT + IR) and combined notching relevant (CNR) ROM (EXT + ER + IR + ADD).

Results

Sta135 showed significantly better ROM for ER, IR, ADD, EXT, CNR ROM, and CIR compared to Ret135 (P < .05) and significantly better EXT and ADD compared to Sta145 (P < .0001). Comparison of Ret135 and Sta145 showed equivalent ROM performance, which was slightly better but nonsignificant for ADD (P = .16), EXT (P = .31), CNR ROM (P = .7), and CIR (P = .54) in favor of Ret135. Isolated IR (P = .39) and ER (P = .32) were slightly better but nonsignificant in favor of a Sta145.

Conclusion

For this implant system tested in a computer model, a 135° standard liner offers the best ROM. A 135° retentive liner maintains at least equivalent CIR and motion to prevent notching compared to a standard 145° liner. 135° retentive liners are more than salvage options and may help to prevent distalization and overtensioning by increased liner thickness.

Keywords

Neck shaft angle
Range of motion
Reverse shoulder arthroplasty
Impingement
Notching
Retentive liner
==== Body
pmcReverse shoulder arthroplasty (RSA) has gained popularity in recent decades due to excellent patient outcomes.28 The initial Grammont-type RSA was designed with a medialized and distalized center of rotation (COR) and a 155° neck-shaft-angle (NSA). This design has had good clinical performance restoring active forward elevation but is associated with some important perioperative complications.6,13 During follow-up, the prototype Grammont arthroplasty showed restriction of rotation, extension (EXT), decreased deltoid wrapping, instability, and notching.8,12 In an attempt to overcome these drawbacks, lateralization of the COR was at first promoted by Frankle with a nonhemispherical glenosphere (GS) and 6-10 mm of inbuilt lateralization of the COR.20 Boileau alternatively proposed using humeral head autograft for glenoid baseplate lateralization, which he coined bony-increased offset RSA.11 Initially, the bony-increased offset RSA was coupled with a 155° stem, resulting in a distalized and lateralized lever arm.10 Later, the NSA was gradually decreased to 145° and 135° with the introduction of the Aequalis Ascend Flex stem (Tornier, Bloomington, MN, USA) in 201214 and now many other implant systems. Although reducing the NSA decreases impingement, the risk of instability due to decreased distalization and a more vertical joint line remains a common complication, ranging from 2.4% to 31%, according to different studies.15,16,22,23,38

Several solutions have been proposed to treat instability after RSA. On the glenoid side, options include increasing the GS diameter and using a lateralized or eccentric sphere. On the humeral side, solutions include increasing the NSA, building up tension with thicker polyethylene inserts, and using retentive liners to provide more constraint. Retentive inserts increase stability by increasing the socket depth either by a deeper dish with less lateralization or the same depth with higher borders of the inlay without changing the amount of lateralization. This creates a more constrained implant, which has significantly affected the force required to dislocate the RSA in biomechanical studies.1,22,35 On the other side, a more constrained design theoretically leads to less range of motion (ROM) and, hence, more impingement and notching. However, in one retrospective clinical study, there was no statistical difference in ROM between patients with retentive and standard inserts.22 Studies on optimizing RSA have focused on impingement-free adduction (ADD) and EXT, aiming to prevent scapular notching.24,30,34 The effects of these modifications on ROM relevant for notching and internal rotation (IR) with the hand to the back are not clearly understood.

When performing RSA with a 135° stem of the implant system tested in this study, superolateral instability associated with the lower NSA may occur without or even after increasing the thickness of the insert. In this situation, after implantation of the GS, the surgeon can either use a retentive 135° liner or change the NSA to 145° with a nonretentive +10° standard insert.

In this computer model study, 3 different liners with identical configurations of the stems and glenoid implants were compared: a standard 135°, a retentive 135°, and a standard 145° insert. Assessment of isolated ROM, combined IR (CIR) and EXT (IR + EXT), and combined notching relevant ROM (CNR ROM) as the sum of IR, external rotation (ER), and EXT with the arm at the side and ADD (IR + ER + EXT + ADD) were performed. The hypothesis was that the ROM with the arm at the side for the 135° retentive inlay has no major drawbacks compared to the 145° insert.

Materials and methods

Study design and population

In this computer model study, we used deidentified computed tomographic (CT) scans of 22 patients (11 males and 11 females with a mean age of 72.9 years; females 74.6 years, males 71.1 years; range 62-83), with massive cuff tears, and the CT was done for routine preoperative planning. Approval from the local ethics committee was granted before the commencement of the study (Ethics committee approval was obtained from the Commission Cantonale d’éthique de la Recherche sur l’être Humain, study no. 2023-01051). Inclusion criteria were Hamada grade 1-2 cuff tear arthropathies with Sirveaux E0-type glenoid without any joint space narrowing, degenerative wear, and bony deformity, which were considered exclusion criteria.

The Digital Imaging and Communications in Medicine images of the CT scans were analyzed using Blueprint software (version 3.0.1; Imascap, Brest, France). After a computed segmentation sequence, the software automatically calculates both version and inclination of the glenoid as previously described and automatically calculates a neutral reference scapular plane based on automatic 3-dimensional reconstruction of all 3-dimensional points of the scapula body. The automated measurement process, reference points, axis, and planes have previously been validated and published in detail.9 The software was used to simulate the rigid body motion (RBM) in a virtual RSA model for the PERFORM RSA system (Stryker, Kalamazoo, MI, USA), based on impingement detection between the bony anatomy and the prosthesis.

The glenoid configuration consisted of a standard PERFORM reverse base plate with a diameter of 25 mm. According to the computed scapular plane, the software automatically positions a selected implant baseplate in a standardized neutral position with 0° inclination and 0° version. In this standardized plane, virtual glenoid preparation was performed with a 25 mm baseplate (PERFORM reversed) positioned flush with the inferior border of the glenoid. The baseplate was +3 mm lateralized for females and +6 mm for males. The GS size was 36 mm for females and 39 mm for males.

The humeral configuration consisted of a PERFORM 135° inlay stem using 3 different inserts as shown in Fig. 1 (Fig. 1): A standard symmetric 135°, a retentive symmetric 135°, and a standard +10° insert (NSA of 145°). The difference between the standard symmetric 135° and retentive symmetric 135° insert is that the latter has an all-around increased lip height of +2 mm for 36 mm and 39 mm as shown in Fig. 2 (Fig. 2). The radius of curvature of the insert remains the same as for regular inserts; however, the constraint ratio is increased by changing the height of the insert. The constraint ratio is defined as d/R (depth of the poly articulation parallel to the NSA / radius of the glenosphere). The thickness of the polyethylene was set to be 3 mm. Using the patient’s physiological humeral retrotorsion, the osteotomy was performed at the anatomical neck level calculated by the software (height of the osteotomy at +0 mm). A size 2 short stem of 34 mm metaphyseal diameter (Perform, Stryker) was selected for females and a size 3 stem of 38 mm metaphyseal diameter for males (Fig. 1). Medial, lateral, inferior, and anteroposterior arm changes were documented as calculated by the software. All configurations were tested for impingement-free ROM in 3 planes computed by the software with the arm at the side: ADD/abduction (ABD), IR/ER, and EXT/flexion (FLE) at 0° of ABD.Figure 1 Illustration of axial images (Top: antero-posterior constraint) and coronal images (Bottom: inferior constraint and distance to posterior scapular pillar). Baseplate placement was flush at the inferior glenoid border, and with +3 mm lateralization for this female patient. Three different inserts and their distance from the posterior pillar of the scapula are shown; 135° standard (A), 135° retentive (B), and 145° standard (C).

Figure 2 Schematic illustration of different inserts with their constraint ratios: 135° standard (A), 135° retentive with a 2 mm all-round higher lip (B), and 145° standard (C) (Top: 36 mm collar diameter, Bottom: 39 mm collar diameter). Courtesy of Stryker.

ER, IR, ADD, and EXT computed as RBM as well as CIR (CIR = IR + EXT) and CNR ROM (CNR ROM = EX + IR + ER + AD) were the outcome variables.

Statistical analysis

The statistical and graphical analysis was performed with R language 4.3.1 (R Foundation for Statistical Computing, Vienna, Austria). Descriptive statistics were used to analyze the distribution of ROM illustrated by box plots. The 1-way analysis of variance was used to examine the differences between the 3 insert groups, with post-hoc pairwise comparison conducted using the t-test. Significance was set at P < .05.

Results

The results are shown in Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Table I.Figure 3 Box-plot comparison of internal rotation (IR) and external rotation (ER) between the 3 groups.

Figure 4 Box-plot comparison of adduction (ADD) and abduction (ABD) between the 3 groups.

Figure 5 Box-plot comparison of extension (EXT) and flexion (FLE) between the 3 groups.

Figure 6 Box-plot comparison of combined internal rotation (EXT + IR) between the 3 groups. EXT, extension; IR, internal rotation.

Figure 7 Box-plot comparison of combined notching relevant range of motion (ADD + IR + ER + EXT) between the 3 groups. ADD; adduction; IR, internal rotation; ER, external rotation; EXT, extension.

Table I Summary of all measured range of motion.

	135 standard insert Mean (min-max)	135 retentive insert Mean (min-max)	145 standard insert Mean (min-max)	
Adduction (ADD)	41 (29-61)	29 (12-44)	26 (15-41)	
Abduction (ABD)	77 (58-98)	75 (58-93)	78 (58-99)	
Internal rotation (IR)	96 (83-106)	87 (71-98)	92 (76-104)	
External rotation (ER)	55 (32-69)	43 (20-58)	42 (23-56)	
Extension (EXT)	87 (32-120)	48 (12-100)	40 (16-96)	
Flexion (FLE)	124 (98-153)	122 (85-199)	121 (97-153)	
IR + EXT	183 (136-223)	135 (95-191)	132 (105-193)	
IR + EXT + ADD + ER	279 (211-333)	207 (127-285)	200 (156-280)	
The measurements are expressed in degree.

Unidirectional range of motion

Concerning unidirectional ROM (Table I), the 135° standard insert had a significantly better ROM in IR and ER compared to the 135° retentive inlay (P = .046 and P < .001, respectively, Fig. 3), but no statistically significant difference compared to the 145° stem (P = .34 and P = .13, respectively). The 135° standard insert had a statistically significantly better ROM in ADD and EXT compared to both the 135° retentive inlay and the 145° standard insert, as expected (P = .0021, P < .001, P = .0021, and P < .001, respectively, Figs. 4 and 5). Concerning ABD and FLE (Figs. 4 and 5), there was no statistically significant difference between the 3 groups (P = .96, P = .78). When comparing the 135° retentive and the 145° standard insert, there was no statistically significant difference in any unidirectional ROM.

Combined range of motion

For the combined ROM (Table I), the 135° standard insert has shown statistically better ROM in both CIR (CIR = EXT + IR) (Fig. 6) and CNR ROM (ADD + IR + ER + EXT) (Fig. 7) compared to the 135° retentive insert and the 145° standard insert (all P < .001). When comparing the 135° retentive to the 145° standard insert, there was no significant difference.

Discussion

The key finding of this study is that there is no statistically significant difference between the ROM of the 135° retentive insert and the 145° standard insert of the tested implant system. The 135° retentive insert does not lead to a specific reduction of ROM and is a good alternative compared to increasing the NSA. It may also help to avoid thicker 135° inserts commonly used in cases with concerns for stability which may cause problems with overstuffing and difficulty repairing subscapularis.

As expected, the stem with a standard 135° insert showed significantly better ROM overall for ADD, EXT, ER, and IR when compared to a standard 145° and 135° retentive insert. ABD and FLE have only minimally been influenced by the change in NSA without statistical significance. A computer simulation study by Arenas-Miquelez et al have shown that increasing NSA increases the ABD at the detriment of ADD, and concluded that the 145° stem gives the best overall ROM. The loss of ABD with the 135° stem and onlay insert was explained by the excessive proximalization and lateralization, causing impingement between the greater tuberosity and the acromion.2 However, in a clinical scenario, the small differences in FLE and ABD between different NSA can be expected to be compensated by scapula motion.4, 5, 6

When comparing the 135° standard insert to the 135° retentive insert, there was a statistically significant difference in favor of the 135° standard insert. However, a clinical study by Abdulla et al with a different implant concluded that a constrained insert does not alter the resultant joint load and the deltoid forces, nor changes the active ROM in ABD, IR, or ER, although a statistically significant difference was observed in passive ER between the high constraint group and the low constraint group.1 This study was, however, performed with a different NSA of 155°, which has a major influence on the effect of a retentive liner in combination with a GS without lateralization. It is also important to point out that there are a range of different constrained liners on the market with different constraint ratios, and therefore, the label “retentive insert” has only a comparative meaning for liners of the same manufacturer and specific type of implant.17,19

Instability after RSA remains an important complication. Using a retentive insert, increasing the NSA, and building up insert thickness leading to increased joint reaction forces have all been shown to increase stability and are the 3 readily available options after intraoperative testing once the glenoid-sided implants are already in place.15,23 When deciding between a retentive insert and an angled insert which increases the NSA, the specific ROM must be considered to provide optimized ROM.

Work by Gerber’s group has shown that functional IR requires at least 40° of active EXT for daily tasks such as tucking shirts or unbuttoning bras.25 Lädermann et al have pointed out that the implantation of RSA results almost always in a diminution of EXT compared to the contralateral side.29 Therefore, we also looked at combined computer-simulated motion for IR (CIR = IR + EXT), which showed no statistical difference in IR + EXT with the retentive 135° insert compared to a standard 145° insert.

Scapular notching has been associated with worse clinical outcomes after RSA.36 Mechanical impingement in IR and ER causes limited passive ROM and glenoid loosing.37 Although changing the NSA from 145° to 135° does not significantly lateralize the humeral implant, the lower NSA does decrease the risk of notching by tilting the polyethylene away from the scapular pillar.7,39 Several studies have pointed out that decreasing NSA improves ADD and avoids notching, but emphasized that increasing GS lateral offset and inferior eccentricity have a positive effect on ER, hence decreasing scapular notching as well.2,4, 5, 6 Neyton compared a 135° stem to a 145° stem at 2 years and found 135° reduced the phenomenon of notching from 53.4% to 30% but failed to notice any clinical differences.33 In a meta-analysis, Holster has shown decreasing the NSA improves ER at the expense of ABD and decreases the rate of notching and, ultimately, dislocation (1.4% for 135° compared to 4.6% for 145°).26 According to a review by Bauer et al,6 the notching phenomenon is influenced by 5 factors:(1) Location of the COR of the GS relative to the glenoid center,

(2) Humeral NSA,

(3) Shape of the scapular pillar,

(4) Shape of the scapular neck (which can be elongated by glenoid lateralization), and

(5) Distance of the scapular pillar in relation to the posteroinferior extent of GS.3

In the present study, a standard 135° insert has significantly greater overall ROM and, therefore, potentially reduces the risk of notching. The effect of retentive inserts on scapular notching is not clearly understood and is difficult to compare because of the heterogenicity of constraint ratios of different manufacturers.19 Kowalsky et al. retrospectively examined 88 patients and found that the retentive insert Zimmer Trabecular Metal Reverse Shoulder System (Zimmer Biomet, Warsaw, IN, USA) has a high rate of notching compared to the nonretentive insert (71% vs. 58%). However, the stem used in the study had a 150° NSA, so the results should be interpreted with caution.27

Anatomical considerations such as lateralization and especially distalization may also play an important role in favor of a more “anatomical” RSA and subscapularis length and orientation if repairable. A more lateralized humeral stem has been shown to restore the anatomical position of the lesser and greater tuberosities, improving the length/tension curve of the remaining cuff.21 A more lateral greater tuberosity increases the ABD angle and improves deltoid wrapping, which ultimately leads to a greater compressive force across the joint surface.18 On the other hand, Levin et al have shown that a lateral glenoid-medial humerus combination with a 135° NSA provides the most anatomical fiber-length relationship for optimized muscle contractility according to the Blix curve.31 If instability is encountered with such an optimized “anatomical” RSA with a 135° NSA, solving the problem with a thicker insert could be detrimental to the repair of subscapularis by adding more humeral lateralization and distalization, with fiber overlengthening and possibly reduced contractility,31 failure of the repair, or even inability to repair the tendon. Furthermore, some patients with hyperlaxity and instability of the RSA may be vulnerable to nerve stretching when the insert thickness is increased as pointed out by Marion et al.32 They recommended avoiding building up the humerus by increasing implant thickness while simultaneously distalizing it since they demonstrated axillary nerve stretching if the summit of the greater tubercle of the humerus was distalized below the equatorial mid-glenoid line. They conclude that alternative options to increase stability should be considered. Given the findings that a retentive 135° inlay is “as good” for ROM as a standard 145° inlay, the threshold to use a retentive 135° instead of an increased thickness 135° inlay should be lowered in the future. Retentive inlays may have had a negative connotation in the past with a 155° NSA being associated as a salvage option with reduced ROM, notching, and decreased implant longevity.

Our study has several strengths. These include a controlled design of both the humeral-sided and glenoid-sided implant guided by a neutral RSA position in the scapular plane computed by the software; the standardized measurement of ROM for IR, ER, EXT, and ADD pertinent for scapular notching; and an even distribution of male and female patients in the study cohort.

Limitations of this study are those inherent to computer modeling studies with RBM of the glenohumeral joint. First, it does not take scapulothoracic motion into account, which delivers a large contribution to FLE and ABD, a lesser degree to EXT, and little contribution to ER and ADD with the “arm at side.” Second, the influence of the soft tissues and muscle forces cannot be accounted for with these. In addition, EXT beyond 60° is not physiological and could be of little clinical relevance. Third, our RBM results are representative for only 1 implant configuration, which cannot reflect the design of all humeral stems with a NSA of 135° and different retentive liners with different “constraint ratios” in the market. Implantation strategies to increase impingement-free ROM, such as anteriorization, posteriorization, change of version, and dialing GS eccentricity more posteriorly, and glenoid strategies to increase stability, such as increasing the GS size and eccentricity, were not explored in this study. Computer model studies assessing RBM are not able to assess the stability of different inserts and this was not the purpose of this study. However, it is mechanically evident that a retentive insert with a higher lip is more stable compared to the same nonretentive insert with a lower lip. Finally, instability in RSA is often multifactorial, and specific etiological factors require a precise diagnosis and specific treatment prior to the use of a constrained liner.

Conclusion

In silico, a 135° retentive liner of the tested implant system offers CIR and CNR ROM, which is at least equivalent to a standard 145° liner. It has the advantages of a less distalized and more “anatomic” RSA, especially if insert thickness is not increased simultaneously.

Acknowledgments

The author (S.B.) sincerely thanks the University of Western Australia and the Australian Government for their support of this work through a Research Training Program PhD scholarship.

Disclaimers:

Funding: No funding was disclosed by the authors.

Conflicts of interest: Stefan Bauer is a consultant for Stryker Osteonics SA without any personal payments; the 10.13039/100015539 Australian Government supported Dr. Bauer as part of a Research Training Program PhD scholarship kindly that is not related to the funding of this study. The other authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

This study was approved by the institutional ethics committee (Commission cantonale d’éthique de la recherche sur l’être humain, CER-VD protocol number 2023-01051), with waiver of patient informed consent.
==== Refs
References

1 Abdulla I. Langohr D.G. Giles J.W. Johnson J.A. Athwal G.S. The effect of humeral polyethylene insert constraint on reverse shoulder arthroplasty biomechanics Shoulder Elbow 10 2018 25 31 10.1177/1758573217701065 29276534
2 Arenas-Miquelez A. Murphy R.J. Rosa A. Caironi D. Zumstein M.A. Impact of humeral and glenoid component variations on range of motion in reverse geometry total shoulder arthroplasty: a standardized computer model study J Shoulder Elbow Surg 30 2021 763 771 10.1016/j.jse.2020.07.026 32763384
3 Bauer S. Blakeney W.G. Goyal N. Flayac H. Wang A. Corbaz J. Posteroinferior relevant scapular neck offset in reverse shoulder arthroplasty: key player for motion and friction-type impingement in a computer model J Shoulder Elbow Surg 31 2022 2638 2646 10.1016/j.jse.2022.06.014 35931331
4 Bauer S. Blakeney W.G. Meylan A. Mahlouly J. Wang A.W. Walch A. Humeral head size predicts baseplate lateralization in reverse shoulder arthroplasty: a comparative computer model study JSES Int 8 2023 335 342 10.1016/j.jseint.2023.11.015 S2666638323002864 38464453
5 Bauer S. Blakeney W.G. Wang A.W. Ernstbrunner L. Corbaz J. Werthel J.-D. Challenges for optimization of reverse shoulder arthroplasty Part II: Subacromial space, scapular posture, moment arms and muscle tensioning J Clin Med 12 2023 1616 10.3390/jcm12041616 36836151
6 Bauer S. Blakeney W.G. Wang A.W. Ernstbrunner L. Werthel J.-D. Corbaz J. Challenges for optimization of reverse shoulder arthroplasty Part I: external rotation, extension and internal rotation J Clin Med 12 2023 1814 10.3390/jcm12051814 36902601
7 Bauer S. Corbaz J. Athwal G.S. Walch G. Blakeney W.G. Lateralization in reverse shoulder arthroplasty J Clin Med 10 2021 5380 10.3390/jcm10225380 34830659
8 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 469 2011 2425 2431 10.1007/s11999-010-1757-y 21210311
9 Boileau P. Cheval D. Gauci M.-O. Holzer N. Chaoui J. Walch G. Automated three-Dimensional measurement of glenoid version and inclination in Arthritic shoulders J Bone Jt Surg 100 2018 57 65 10.2106/JBJS.16.01122
10 Boileau P. Moineau G. Roussanne Y. O’Shea K. Bony increased offset-reversed shoulder arthroplasty (BIO-RSA). JBJS Essent Surg Tech 7 2017 e37 10.2106/JBJS.ST.17.00006
11 Boileau P. Morin-Salvo N. Gauci M.-O. Seeto B.L. Chalmers P.N. Holzer N. Angled BIO-RSA (bony-increased offset–reverse shoulder arthroplasty): a solution for the management of glenoid bone loss and erosion J Shoulder Elbow Surg 26 2017 2133 2142 10.1016/j.jse.2017.05.024 28735842
12 Boileau P. Watkinson D. Hatzidakis A.M. Hovorka I. Neer award 2005: the Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture sequelae, and revision arthroplasty J Shoulder Elbow Surg 15 2006 527 540 10.1016/j.jse.2006.01.003 16979046
13 Boileau P. Watkinson D.J. Hatzidakis A.M. Balg F. Grammont reverse prosthesis: design, rationale, and biomechanics J Shoulder Elbow Surg 14 2005 S147 S161 10.1016/j.jse.2004.10.006
14 Bradley Edwards T. Morris B.J. Hodorek B. Tornier Aequalis AscendTM Flex Convertible shoulder system Frankle M. Marberry S. Pupello D. Reverse shoulder arthroplasty 2016 Springer International Publishing Cham 441 447 10.1007/978-3-319-20840-4_44 ISBN 978-3-319-20839-8
15 Chae J. Siljander M. Wiater J.M. Instability in reverse total shoulder arthroplasty J Am Acad Orthop Surg 26 2018 587 596 10.5435/JAAOS-D-16-00408 30074512
16 Cheung E. Willis M. Walker M. Clark R. Frankle M.A. Complications in reverse total shoulder arthroplasty J Am Acad Orthop Surg 19 2011 439 449 10.5435/00124635-201107000-00007 21724923
17 Cogan C.J. Ho J.C. Entezari V. Iannotti J.P. Ricchetti E.T. The influence of reverse total shoulder arthroplasty implant design on biomechanics Curr Rev Musculoskelet Med 16 2023 95 102 10.1007/s12178-023-09820-8 36735182
18 Costantini O. Choi D.S. Kontaxis A. Gulotta L.V. The effects of progressive lateralization of the joint center of rotation of reverse total shoulder implants J Shoulder Elbow Surg 24 2015 1120 1128 10.1016/j.jse.2014.11.040 25601382
19 Elwell J. Athwal G. Willing R. Maximizing range of motion of reverse total shoulder arthroplasty using design optimization techniques J Biomech 125 2021 110602 10.1016/j.jbiomech.2021.110602
20 Frankle M. Levy J.C. Pupello D. Siegal S. Saleem A. Mighell M. The reverse shoulder prosthesis for glenohumeral arthritis associated with severe rotator cuff deficiency J Bone Joint Surg Am 87 2005 1697 1705 10.2106/JBJS.D.02813 16085607
21 Giles J.W. Langohr D.G.G. Johnson J.A. Athwal G.S. Implant design variations in reverse total shoulder arthroplasty influence the required deltoid force and resultant joint load Clin Orthop 473 2015 3615 3626 10.1007/s11999-015-4526-0 26310680
22 Goodloe J.B. Denard P.J. Lederman E. Gobezie R. Werner B.C. No difference in range of motion in reverse total shoulder arthroplasty using standard or constrained liners: a matched cohort study JSES Int 6 2022 929 934 10.1016/j.jseint.2022.07.004 36353430
23 Guarrella V. Chelli M. Domos P. Ascione F. Boileau P. Walch G. Risk factors for instability after reverse shoulder arthroplasty Shoulder Elbow 13 2021 51 57 10.1177/1758573219864266 33717218
24 Gutiérrez S. Comiskey C.A. Luo Z.-P. Pupello D.R. Frankle M.A. Range of impingement-free abduction and adduction deficit after reverse shoulder arthroplasty: Hierarchy of Surgical and implant-design-related factors J Bone Jt Surg Am 90 2008 2606 2615 10.2106/JBJS.H.00012
25 Hochreiter B. Wyss S. Gerber C. Extension of the shoulder is essential for functional internal rotation after reverse total shoulder arthroplasty J Shoulder Elbow Surg 31 2022 1166 1174 10.1016/j.jse.2021.11.006 34968695
26 Holsters L. Sadeghi N. Gendera H. Groen V. Bruls V. Lambers Heerspink O. Influence of humeral stem inclination in reverse shoulder arthroplasty on range of motion: a meta-analysis JSES Rev Rep Tech 1 2021 102 112 10.1016/j.xrrt.2021.02.002 37588151
27 Kowalsky M.S. Galatz L.M. Shia D.S. Steger-May K. Keener J.D. The relationship between scapular notching and reverse shoulder arthroplasty prosthesis design J Shoulder Elbow Surg 21 2012 1430 1441 10.1016/j.jse.2011.08.051 22079766
28 Kozak T. Bauer S. Walch G. Al-karawi S. Blakeney W. An update on reverse total shoulder arthroplasty: current indications, new designs, same old problems EFORT Open Rev 6 2021 189 201 10.1302/2058-5241.6.200085 33841918
29 Lädermann A. Denard P.J. Boileau P. Farron A. Deransart P. Terrier A. Effect of humeral stem design on humeral position and range of motion in reverse shoulder arthroplasty Int Orthop 39 2015 2205 2213 10.1007/s00264-015-2984-3 26381907
30 Lädermann A. Gueorguiev B. Charbonnier C. Stimec B.V. Fasel J.H.D. Zderic I. Scapular notching on Kinematic simulated range of motion after reverse shoulder arthroplasty is not the result of impingement in adduction Medicine (Baltimore) 94 2015 e1615 10.1097/MD.0000000000001615
31 Levin J.M. Pugliese M. Gobbi F. Pandy M.G. Di Giacomo G. Frankle M.A. Impact of reverse shoulder arthroplasty design and patient shoulder size on moment arms and muscle fiber lengths in shoulder abductors J Shoulder Elbow Surg 32 2023 2550 2560 10.1016/j.jse.2023.05.035 37419441
32 Marion B. Leclère F.M. Casoli V. Paganini F. Unglaub F. Spies C. Potential axillary nerve stretching during RSA implantation: an anatomical study Anat Sci Int 89 2014 232 237 10.1007/s12565-014-0229-y 24497198
33 Neyton L. Nigues A. McBride A.P. Giovannetti De Sanctis E. Neck shaft angle in reverse shoulder arthroplasty: 135 vs. 145 degrees at minimum 2-year follow-up J Shoulder Elbow Surg 32 2023 1486 1493 10.1016/j.jse.2022.12.014 36690171
34 Nicholson G.P. Strauss E.J. Sherman S.L. Scapular notching: Recognition and strategies to minimize clinical impact Clin Orthop 469 2011 2521 2530 10.1007/s11999-010-1720-y 21128030
35 Sheth U. Saltzman M. Reverse total shoulder arthroplasty: implant design considerations Curr Rev Musculoskelet Med 12 2019 554 561 10.1007/s12178-019-09585-z 31721016
36 Simovitch R. Flurin P.-H. Wright T.W. Zuckerman J.D. Roche C. Impact of scapular notching on reverse total shoulder arthroplasty midterm outcomes: 5-year minimum follow-up J Shoulder Elbow Surg 28 2019 2301 2307 10.1016/j.jse.2019.04.042 31311751
37 Spiry C. Berhouet J. Agout C. Bacle G. Favard L. Long-term impact of scapular notching after reverse shoulder arthroplasty Int Orthop 45 2021 1559 1566 10.1007/s00264-021-04998-3 33723643
38 Teusink M.J. Pappou I.P. Schwartz D.G. Cottrell B.J. Frankle M.A. Results of closed management of acute dislocation after reverse shoulder arthroplasty J Shoulder Elbow Surg 24 2015 621 627 10.1016/j.jse.2014.07.015 25441563
39 Werthel J.-D. Walch G. Vegehan E. Deransart P. Sanchez-Sotelo J. Valenti P. Lateralization in reverse shoulder arthroplasty: a descriptive analysis of different implants in current practice Int Orthop 43 2019 2349 2360 10.1007/s00264-019-04365-3 31254018
