Current designs and trends in reverse shoulder arthroplasty

Transcription

1 Page 1 of 7 Surgical Procedures NP Sachinis*, P Athanasiadou Current designs and trends in reverse shoulder arthroplasty Abstract Introduction The need for finding a suitable treatment for patients suffering from cuff tear arthropathy has been the basis for the evolvement of reverse shoulder arthroplasty. This unorthodox implant with promising but not very satisfactory results, when early design results were reported, has seen a substantial increase in the recent years in the creation of new prostheses and implantations. All designs that exist so far and their alterations according to the first Delta prosthesis are being analysed in this review. Discussion The Delta design has been the one with most reports in the international literature. Based on this design, several other prostheses have been developed. The complications, which have been encountered in early reports, have triggered alterations on the new Delta and on other implants. As expected, no new studies with long-term follow-up of new designs exist, while other models have yet to demonstrate any reported outcomes. Conclusion Reverse shoulder arthroplasty has originated from the necessity of treating several troublesome pathologies. This recent plethora of reverse shoulder systems is manufactured in order to limit the rate of all complications reported in early designs. Future studies should permit for the resolution of troublesome complications and discover which implant * Corresponding author nick.sachinis@gmail.com A Orthopaedic Department, Aristotle University of Thessaloniki, G. Papanikolaou General Hospital, Thessaloniki, Greece or implants offer an optimum survival rate along with above-average clinical outcomes. Introduction There is a distinctive point in the history for the treatment of each joint. For the shoulder, it was the dead-end of standard total shoulder arthroplasty in providing solid results when dealing with patients suffering from rotator cuff deficiency 1,2 (Figure 1). It was then when several surgeons in the 1970s began designing shoulder arthroplasties but reversed the ballsocket anatomy, hoping for improved outcomes 3. From 1972 until 1985, eight major designs were clinically tested, from the Leeds Shoulder up to the trispherical design, in hope of eliminating the risks of dislocation and loosening and improving range and strength 3. The results of these prostheses were not as favourable as expected. In 1985, Dr Paul Grammont designed a different system which demonstrated four features, in order to improve the clinical results: inherent stability of the prosthesis, a convex implant on the glene and a concave one on the humeral side, transfer of the centre of the sphere at or within the glenoid neck and a medialised, distalised centre of rotation (COR) 4. As the initial Grammont implant got redesigned several times 5, from Figure 1: Cases in which a reverse shoulder arthroplasty is indicated as a second procedure (salvage). (a) Hemiarthroplasty of the shoulder in a patient with a rotator cuff deficiency has resulted in superior migration of the humerus and arthritic changes around the acromion and glenoid. (b) Cuff deficiency in a patient with total shoulder arthroplasty. Again superior migration is evident, along with displacement of the glenoid component. (c) Loosening (aseptic in this figure) of a hemiarthroplasty. Although in this case, superior migration is not evident in plain x-rays, if the patient is diagnosed by other means (e.g. magnetic resonance imaging) with rotator cuff deficiency, then a reverse shoulder arthroplasty is indicated.

2 Page 2 of until 2013, new implants have arisen that focus on reverse shoulder arthroplasty. Indications for doing a reverse shoulder arthroplasty have been also expanded. They have been implemented not only for cuff-deficient arthritic shoulders, but also in cases of trauma, rheumatoid arthritis, tumours and revisions of other shoulder arthroplasties 6 (Figure 2). This review is focused in highlighting current designs of reverse shoulder replacements and analysing the studies that centre on them. We performed a review of the English literature, using a PubMed search with the terms reverse, shoulder, arthroplasty and replacement, and we found 381 articles. Also, we performed a web-based search by using the same keywords on several search engines. From all retrieved articles and websites, after investigation for current designs, we finally investigated the prostheses that are displayed in Table 1. Discussion The Delta Xtend Reverse Shoulder System (De Puy, J&J Company) is the latest implant in the Delta reverse series, which started from the design of Dr Paul Grammont, the Delta I, in It consists of a cementless titanium modular hydroxyapatite (HA)-coated or monobloc cobalt chromium alloy (Co Cr) cemented stem, variable thickness polyethylene (PE) cup and a glenoid component with a central peg and cannulated screws. The features of this design on the humeral prosthesis are a nonanatomic neck shaft angle, which was presented on the previous model, a fluted humeral stem and thinner monobloc humeral stem for cemented purposes. The metaglene has a curved back design for preserving bone, and the joint COR is on the glenoid surface for reducing pull-out torques. There is also an inferior overlap of the glenoid component in order to avoid scapular neck erosion and maximise the range of motion (ROM). Figure 2: X-rays of patients in which a reverse shoulder arthroplasty was used (a) for arthritis combined with a deficient rotator cuff and (b) for treating a periprosthetic fracture of the humerus. For both cases, the same principles exist when placing the components, although for fracture cases, a long humeral stem and a cement technique are considered as necessary. The Delta system is the most studied in English literature. For the first design, Delta I, Grammont et al. 4 in 1987 published a series of eight patients with impressive short-term results in terms of motion. At 6 months follow-up, three of the eight designs demonstrated 100 to 130 of elevation, despite the preoperative cuff deficiency. Later on, the follow-up cases of loosening of the glenoid component were seen, and this was attributed to the lateral COR, in regard to the natural glenoid. Sirveaux et al. 7 in a multicentre study reviewed 80 shoulders with an average follow-up of 44 months. Although only three of the implants were revised, when glenosphere or humeral component loosening were considered on the survival analysis, survivorship was 91.3% at 5, 74.6% at 7 and only 29.8% at 8 years. The poor survival was mostly attributed due to the initial 11 monobloc implants which were placed on the first years of the study. Two years later, Guery along with the previous group of authors 8 published a continuation of the study. What was defined from their survival results was that early loosening was mostly seen up to 3 years from surgery and was responsible for the first drop of the curve. Progressive deterioration of function was responsible for the second drop of the survival line. The authors finally indicated reserving the procedure only for patients over 70 with low functional demands. The next model of the series, Delta III, was studied prospectively by Klein et al. 9, in 20 patients with comminuted fractures of the proximal humerus, with a mean follow-up of 33 months (range months). Mean elevation was 122, Constant score 10 was 68 and the American Shoulder and Elbow Surgeon (ASES) score 11 was 68. Radiographic analysis showed no evidence of glenoid or humeral loosening, one demonstrated a Nerot-Sirveaux et al. 7 grade I inferior notching and one had two dislocations. No revision was done until the latest follow-up. Naveed et al. 5 reported a single-centre study of 50 serial cases with the Delta III reverse implant. Mean follow-up was 39 months (8 81 months) and most of the

3 Page 3 of 7 Table 1 Specific variables in available reverse shoulder arthroplasty designs Design/company Glenoid Humerus Delta Xtend (Johnson & Johnson) Trabecular metal reverse (Zimmer) Aequalis Reverse (Tornier) Comprehensive Reverse Shoulder System (Biomet) SMR (Lima) Equinoxe Reverse Shoulder (Exactech) Titan Reverse Shoulder System (Integra Lifesciences) Vaios Reverse Shoulder Replacement System (JRI Orthopedics Ltd) Promos Modular Shoulder System (Smith&Nethew) Univers Reverse (Arthrex) HA coating Four screw holes with variable angle Locking cannulated screws Eccentric glenosphere available Revision glenoid bearing tray with four hole plate available Tantalum coating Variable peg length Two screw holes with variable angle Locking screw cap No central hole on glenosphere 36 or 40 mm glenospheres HA coating Four screw holes with variable angle Locking head screws Hemispherical heads for compression 36 or 42 mm glenospheres Porous plasma spray coating Four base plate sizes Four screw holes 36 or 41 mm glenospheres Porotitanium + HA coating Variable peg diameter Two base plate sizes Two screw holes Only 36 mm glenosphere Eccentric glenosphere available Two peg design No inferior screw PE glenosphere Titanium with asymmetrical bead sintered coating Central compression screw with peripheral polyaxial locking screws Eccentric design available Polished Co Cr 2 glenoid coverage sizes conforming or 4 mm radial mismatch for each head size Two fixed-angle, locking head glenoid bone screws Eccentric available Two diameters (36 mm, 42 mm) Co Cr glenosphere TPS/CaP-coated titanium glenoid base plate and titanium screws Modular uncemented stem Monoblock cemented fracture stem Cuff tear arthropathy head +3, +6, +9 mm offset Monoblock metaphysis available 0, +3, +6 mm offsets Modular metaphysis +6, +9, +12 mm offsets Modular metaphysis +6, +8 mm offsets 45 /135 neck-shaft angle Modular metaphysis Cuff tear arthropathy head Co Cr inlay Special fracture inverse system Co Cr cemented or titanium with porous coating uncemented neck-shaft angle H-A.C. Supravit coated titanium or cemented stems 150 neck-shaft angle Taper lock with set screw 155 neck-shaft angle Titanium humeral stem 135 or 155 neck-shaft angle

4 Page 4 of 7 Table 1 (Continued) Design/company Glenoid Humerus Encore, RSP (DJO) Affinis Inverse Shoulder System (Mathys) HA coating Available diameter 32, 36, 40 mm in neutral and 4 mm offsets Inverted materials (PE-Glenosphere, Co Cr in lay) Metaglene with 2-peg fixation All designs have metal backed titanium base plates. All have cemented and uncemented stems. All have metaphyseal suture holes. All have metaphyseal extension to increase length. All use ultrahigh-molecular-weight polyethylene All are convertible to hemiarthroplasty except Biomet s Comprehensive Reverse Shoulder System HA, hydroxyapatite; Co Cr, cobalt chromium; PE, polyethylene. Titanium alloy cemented stem Titanium alloy shells available in neutral, +4, +8 mm offsets 135 neck-shaft angle on RSP design Co Cr inlay 155 neck-shaft angle Eccentric implant positioning Revision/fracture implants Small metaphysical implant (bone saving) patients (43/50) suffered from cuff tear arthropathy (CTA). At final follow-up, ASES score was 65, Oxford score 12 was 23 and elevation had a mean of 105. Four patients required a second operation. Boileau et al. 13, in their clinical study in 2006, reported the midterm results of 45 patients with the Grammont prosthesis. Mean followup was 40 months (24 72 months). From the patient pool, 45 had CTA, 5 had a fracture and 19 cases underwent a revision arthroplasty. At the final follow-up, the authors observed 10 (22%) reoperations, of which four were revisions and two were removals, in a total of 14 complications. Complications were significantly higher in the revision group (47% vs. 5% in CTA group). Average elevation on all groups was 121, Constant score was 58. All scores were significantly higher in the CTA group. The authors suggested that better results are seen, regarding external rotation when teres minor is functional. They also point that surgeons should be cautious of low-grade infection in cases of revision arthroplasty. Realising the need for solid fixation between bone and metal at the base plate, Zimmer (Inc., Warsaw, IN) produced the Trabecular Metal Reverse Shoulder System (TMRS). The prosthesis was first applied in March 2006 and incorporates several alterations to the design and materials related to the Delta implants. As stated by one of the designers 14, Dr Gregory Nicholson, the implant still respects the acknowledged concepts of inferiorisation and medialisation of the glenoid COR. Instead of HA, the implant integrates porous tantalum on the base plate, its central peg and on the proximal side of the humeral stem. As researched in published studies 15,16, this metal with high volume porosity has high friction and increased capability of soft tissue and bone ingrowth later at 8 weeks approximately. In order to prevent scapular notching, a complication recognised even by early Delta implants, the humeral stem has a low profile with no metal above the humeral osteotomy 14. Also, it features a neck-shaft angle of 143 and a PE 7 angle, totalling in an angle of 150. The glenoid base plate is manufactured in order to be placed with a small lateral offset and also inferiorly 14. There are only short-term studies regarding TMRS reaching up to 2 years. Bogle et al. 17 recently published a radiographic review of x-rays of 98 serial shoulders with TMRS, taken at 2 weeks, 1 year and 2 years postoperatively. Shoulders were evaluated for radiolucent lines and for scapular notching. Loosening was absent in 93.9% of humeral implants on the first and 89.5% on the second year. Lucency was no more than 2 mm or in more than one zone in any stem. No glenoid component shows signs of radiolucency. Concerning scapular notching, on the second year, 34.2% had type one notching, 5.3% type two and 2.6% type 3 notching. The authors concluded that in the short term, the results of scapular notching were comparable to previous studies and did not affect implant stability. Dr Gregory Nicholson reports on a review 14 in 2011 that on his ongoing clinical series, he detected no scapular notching at 6 months and 8% at 14 months. Lima LTO (Italy) has produced the SMR (Systema Multiplana Randelli) prosthesis and recently the SMR HP design. The main difference between the two designs is that the HP has a PE glenosphere, instead of the standard metal design and the PE insert; this has been advocated by the company in order to reduce scapular notching. Young et al. 18 first published on the SMR with a series of 55 consecutive patients (56 shoulders). In order to

5 Page 5 of 7 improve fixation at the glene, SMR has a curved back, HA coating and a large tapered central peg, with the option of inserting screws at variable angles. The authors followed the patients for a mean of 38 months (49 shoulders until latest follow-up), where 92% of them reported no or minimal pain with a visual analogue scale (VAS) score. Mean ASES score was 70.1 and average anterior elevation was 122. There were three operative complications and one postoperative dislocation that was reduced under general anaesthesia. The incidence of scapular notching was observed in 12 patients (24%, all under 5 mm). No evidence of loosening on the glenoid fossa and no reoperations were reported until the latest follow-up. Encore reverse shoulder (DJO Surgery, TX) consists of a Co Cr glenoid head implant tapered to a titanium glenoid base plate with a HA coating plasma sprayed over the 3D Matrix porous coating on the backside. Its humeral implant consists of a titanium stem with cement flutes and a humeral socket implant of a titanium shell that snaps into a 4 mm thick compression moulded PE insert. Though its manufacturers do not include trauma as an indication for this implant, Maroney et al. 19 used the prosthesis on a 67-year-old woman with a fracture dislocation of the proximal humerus. At the final follow-up, the patient s clinical outcome was found satisfactory 19. Another case report by Levy and Blum 20, also in 2009, presents scapular notching in a 2-year follow-up of a patient who received an alternative glenosphere as the Encore s reverse shoulder prosthesis (RSP), with a COR 2 mm lateral to the glenoid. The altered COR is also the object of a study by Saltzman et al., in anteroposterior and axillary radiographs taken before and after reverse arthroplasties of 68 patients divided into two groups, where the Encore and Delta III were used. They concluded that COR changes in reverse shoulder arthroplasty, in relation to the shoulder anatomy, and this alteration varies among designs 21. DJO has produced a newer design, RSP, with modifications and a neck-shaft angle of 135 in order to avoid the incidence of scapular notching. The Aequalis Reverse II Shoulder prosthesis (Tornier Inc., Amsterdam) was designed 13 years ago (as Aequalis I), based on the principle of kinematic balancing of the shoulder based on a model initiated by Professor Grammont. Its humeral implant consists of a Co Cr stem and metaphysis, with a PE plug to secure fixation between the metaphysis and the stem; it features four ranges of PE inserts. The glenoid implant consists of the glenoid sphere and base plate, which are designed to enhance primary fixation with a press-fit conical central post and four peripheral screws and secondary fixation with HA coating. The Reverse II Fracture humeral implant is different from the Reverse II standard, as the one who is made for fractures has a metaphysis covered by HA coating, to enhance osteointegration of tuberosities, a metaphysis window, for the use of bone graft material, and polished neck to allow passage of suture. Berhouet et al., in a cadaveric study, investigated 40 shoulders with the Reverse II Aequalis Prosthesis in order to evaluate the ROM of the shoulder and the rate of inferior scapular impingement. The results of their analysis after several combinations were that the most efficient way to prevent scapular notching was to insert the humeral component in 10 to 20 or in the patient s anatomical position 22. Edwards et al. in 2009 evaluated 138 reverse shoulder arthroplasties, where the subscapularis muscle was not repaired in 76 of them. After surgery, seven dislocations took place, all of them from the irreparable group. They concluded that there is greater danger for dislocation when the subscapularis tendon cannot be repaired 23. Wierks et al. followed-up 20 patients with the Aequalis Reverse system. After an average of 9 months follow-up, the authors reported 22 intraoperative and 11 postoperative complications in 15 patients and nine patients with heterotopic ossification. In conclusion, they came up with greater rates of complication in relation to literature 24. Another reverse prosthesis, Equinoxe of Exactech Inc (Gainesville, Florida), has been designed based on the principles of Delta III, but also in order to improve its weaknesses. Equinoxe combines a medialised COR along with a curved glenoid metal plate, which has a unique cylindrical hollow peg with holes in order to augment bone ingrowth and graft insertion. The humeral stem can be used for primary standard and for reverse arthroplasties and has less angle than the Grammont design in order for the humerus to be lateralised, without lateralising the COR 25. Patel et al. in 2012 published a case series of 28 shoulders with an average follow-up of 40.7 months. The patients has a failed primary arthroplasty which was revised to a reverse implant. At final follow-up, ASES averaged at 66.2, forward elevation to 108. The event of scapular notching was not reported in this series, as the authors found only three complications (10.7%) which consisted of a periprosthetic fracture, an infection and an anterior shoulder dislocation. Several other recent designs exist, all based on the initial concept of Grammont prosthesis but with particular modifications, in hope of eliminating the adverse effects of glenoid loosening and scapular notching and prolonging implant survival. To the author s knowledge, there are no clinical trials published in peer-reviewed journals yet which centre on these implants. The Titan Reverse Shoulder System (Integra Lifesciences Holdings Corp) is a recent prosthesis with a platform stem ( cementless or

6 Page 6 of 7 cemented) which offers the ability to interchange components depending on the arthroplasty (primary standard, reverse). Vaios Inverse Shoulder Replacement System (JRI Orthopaedics Ltd) has a curved metal glenoid back to improve load distribution with a large tapered peg and the ability to insert four locking screws. It also has the ability to interchange components between standard and reverse arthroplasty without the need to change the metal glenoid back. Promos Modulas Shoulder System (Smith & Nephew) has a reverse option along with its regular model. The glenoid base plate has a central peg and allows for fixation with two fixed-angle locking screws. Similar to most other options, it combines a metal glenosphere, a PE insert and a stem that can be used for the regular and reverse designs. The Univers Revers (Arthrex) is another inverse implant that medialises and inferiorises the COR of the shoulder joint which as per Grammont s and other Delta studies 3,4,7,26 can lengthen the lever arm of the deltoid and increase tension of the muscle. The Univers Revers has a variable humeral-shoulder inclination angle of 135 or 155 in order to prevent scapular notching, and the humeral part can be fixed either cemented or cementless. The Comprehensive Reverse Shoulder System is a design produced by Biomet. It has a porous plasma spray coating proximally to enhance bone integration, a 45 /135 neck-shaft angle and an exclusive RingLoc locking mechanism between the humeral tray and PE bearing. The above system also allows for removal and exchange of the insert without disruption of the humeral tray or stem. The Affinis Inverse Shoulder System (Mathys) features a change on the articulation couple by having an eccentric PE glenosphere (similar to the SMR HP), so that no PE debris will be produced on the scapular notch. Unlike other designs it has two pegs on the glenoid base plate and the possibility inserting two screws, the one in-between of the pegs. Conclusion Reverse shoulder arthroplasty has originated from the necessity of treating several troublesome pathologies. Mostly entailed are pseudoparalysis from massive unrepairable rotator cuff tears, failed primary standard arthroplasties and fractures of the proximal humerus in elderly patients with deficient rotator cuffs. Although this, not so new now, concept can deliver significant improvements in several clinical aspects such as pain relief, forward elevation and overall satisfaction, many concerns remain. Complications of the operation involve prosthetic loosening (mostly on the glenoid fossa), deltoid tensioning, decoaptation (resulting in dislocation), scapular notching and limitations in external and internal rotation. This recent plethora of reverse shoulder systems, as discussed above, is manufactured in order to limit the rate of all complications reported in early designs. Surgeons experience plays a significant role in decreasing any perioperative and postoperative problems, along with careful selection of the ideal candidate for this procedure. All clinical studies so far regarding current implants have a short-term follow-up and are vastly cohort studies, which depict the recent experience of a surgeon with a certain design. Future studies should permit for resolution of troublesome complications such as glenoid loosening and scapular notching and discover which implant or implants offer an optimum survival rate along with above-average clinical outcomes. Abbreviations list ASES, American Shoulder and Elbow Surgeon; Co Cr, cobalt chromium alloy; COR, centre of rotation; CTA, cuff tear arthropathy; HA, hydroxyapatite; PE, polyethylene; ROM, range of motion; RSP, reverse shoulder prosthesis; TMRS, Trabecular Metal Reverse Shoulder System; VAS, visual analogue scale. References 1. Franklin JL, Barrett WP, Jackins SE, Matsen FA 3rd. Glenoid loosening in total shoulder arthroplasty. Association with rotator cuff deficiency. J Arthroplasty. 1988;3(1): Wirth MA, Rockwood CA Jr. Complications of total shoulder-replacement arthroplasty. J Bone Joint Surg Am Apr;78(4): Flatow EL, Harrison AK. A history of reverse total shoulder arthroplasty. Clin Orthop Relat Res. 2011;469(9): Grammont P TP, Laffay J, Deries X. Concept study and realization of a new total shoulder prosthesis. Rhumatologie. 1987;39: Naveed MA, Kitson J, Bunker TD. The Delta III reverse shoulder replacement for cuff tear arthropathy: a single-centre study of 50 consecutive procedures. J Bone Joint Surg Br Jan;93(1): Mahmood A, Malal JJ, Waseem M. Reverse shoulder arthroplasty a literature review. Open Orthop J Sep;7: Sirveaux F, Favard L, Oudet D, Huquet D, Walch G, Mole D. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff. Results of a multicentre study of 80 shoulders. J Bone Joint Surg Br Apr;86(3): Guery J, Favard L, Sirveaux F, Oudet D, Mole D, Walch G. Reverse total shoulder arthroplasty. Survivorship analysis of eighty replacements followed for five to ten years. J Bone Joint Surg Am Aug;88(8): Klein M, Juschka M, Hinkenjann B, Scherger B, Ostermann PA. Treatment of comminuted fractures of the proximal humerus in elderly patients with the Delta III reverse shoulder prosthesis. J Orthop Trauma Nov Dec;22(10): Constant CR, Murley AH. A clinical method of functional assessment of the shoulder. Clin Orthop Relat Res Jan;(214): Michener LA, McClure PW, Sennett BJ. American shoulder and elbow surgeons standardized shoulder assessment form,

7 Page 7 of 7 patient self-report section: reliability, validity, and responsiveness. J Shoulder Elbow Surg Nov Dec;11(6): Dawson J, Fitzpatrick R, Carr A. Questionnaire on the perceptions of patients about shoulder surgery. J Bone Joint Surg Br Jul;78(4): Boileau P, Watkinson D, Hatzidakis AM, Hovorka I. Neer Award 2005: the Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture sequelae, and revision arthroplasty. J Shoulder Elbow Surg Sep Oct;15(5): Nicholson GP, Strauss EJ, Sherman SL. Scapular notching: Recognition and strategies to minimize clinical impact. Clin Orthop Relat Res Sep;469(9): Hacking SA, Bobyn JD, Toh K, Tanzer M, Krygier JJ. Fibrous tissue ingrowth and attachment to porous tantalum. J Biomed Mater Res Dec;52(4): Bobyn JD, Stackpool GJ, Hacking SA, Tanzer M, Krygier JJ. Characteristics of bone ingrowth and interface mechanics of a new porous tantalum biomaterial. J Bone Joint Surg Br Sep;81(5): Bogle A, Budge M, Richman A, Miller RJ, Wiater JM, Voloshin I. Radiographic results of fully uncemented trabecular metal reverse shoulder system at 1 and 2 years follow-up. J Shoulder Elbow Surg Apr;22(4):e Young SW, Everts NM, Ball CM, Astley TM, Poon PC. The SMR reverse shoulder prosthesis in the treatment of cuff-deficient shoulder conditions. J Shoulder Elbow Surg Jul Aug;18(4): Maroney SS, Devinney DS. Intrathoracic fracture-dislocation of the proximal humerus treated with reverse total shoulder arthroplasty. Orthopedics Dec;32(12): Levy J, Blum S. Inferior scapular notching following encore reverse shoulder prosthesis. Orthopedics. 2009;32(10): Saltzman MD, Mercer DM, Warme WJ, Bertelsen AL, Matsen FA 3rd. A method for documenting the change in center of rotation with reverse total shoulder arthroplasty and its application to a consecutive series of 68 shoulders having reconstruction with one of two different reverse prostheses. J Shoulder Elbow Surg Oct;19(7): Berhouet J, Garaud P, Favard L. Evaluation of the role of glenosphere design and humeral component retroversion in avoiding scapular notching during reverse shoulder arthroplasty. J Shoulder Elbow Surg Feb;23(2): Edwards TB, Williams MD, Labriola JE, Elkousy HA, Gartsman GM, O Connor DP. Subscapularis insufficiency and the risk of shoulder dislocation after reverse shoulder arthroplasty. J Shoulder Elbow Surg Nov Dec;18(6): Wierks C, Skolasky RL, Ji JH, Mc- Farland EG. Reverse total shoulder replacement: intraoperative and early postoperative complications. Clin Orthop Relat Res Jan;467(1): Roche C, Flurin PH, Wright T, Crosby LA, Mauldin M, Zuckerman JD. An evaluation of the relationships between reverse shoulder design parameters and range of motion, impingement, and stability. J Shoulder Elbow Surg Sep Oct;18(5): Grammont PM, Baulot E. Delta shoulder prosthesis for rotator cuff rupture. Orthopedics Jan;16(1):65 8.