Does arm lengthening affect the functional outcome in onlay reverse shoulder arthroplasty?

Biomechanical Characteristics of Glenosphere Orientation Based on Tilting Angle and Overhang Changes in Reverse Shoulder Arthroplasty

Background

Glenoid position and inclination are important factors in protecting against scapular notching, which is the most common complication that directly affects the longevity of reverse shoulder arthroplasty (RSA). This study aimed to investigate the biomechanical characteristics of glenosphere orientation, comparing neutral tilt, inferior overhang with an eccentric glenosphere at the same placement of baseplate, and inferior tilt after 10° inferior reaming in the lower part of the glenoid in RSA.

Methods

Nine cadaveric shoulders were tested with 5 combinations of customized glenoid components: a centric glenosphere was combined with a standard baseplate (group A); an eccentric glenosphere to provide 4-mm inferior overhang than the centric glenosphere was combined with a standard baseplate (group B); a centric glenosphere was combined with a wedge-shaped baseplate tilted inferiorly by 10° with the same center of rotation (group C); an eccentric glenosphere was attached to a wedge-shaped baseplate (group D); and 10° inferior reaming was performed on the lower part of the glenoid to apply 10° inferior tilt, with a centric glenosphere secured to the standard baseplate for simulation of clinical tilt (group E). Impingement-free angles for adduction, abduction, forward flexion, external rotation, and internal rotation were measured. The capability of the deltoid moment arm for abduction and forward flexion, deltoid length, and geometric analysis for adduction engagement were evaluated.

Results

Compared with neutral tilt, inferior tilt at the same position showed no significant difference in impingement-free angle, moment arm capability, and deltoid length. However, group D resulted in better biomechanical properties than a central position, regardless of inferior tilt. Group E demonstrated a greater range of adduction, internal and external rotation, and higher abduction and forward flexion capability with distalization, compared to corresponding parameters for inferior tilt with a customized wedge-shaped baseplate.

Conclusions

A 10° inferior tilt of the glenosphere, without changing the position of the baseplate, had no benefit in terms of the impingement-free angle and deltoid moment arm. However, an eccentric glenosphere had a significant advantage, regardless of inferior tilt. Inferior tilt through 10° inferior reaming showed better biomechanical results than neutral tilt due to the distalization effect.

The association between humeral lengthening and clinical outcomes after reverse shoulder arthroplasty: a systematic review and meta-analysis

BACKGROUND

The purpose of this study was to evaluate the relationship between humeral lengthening and clinical outcomes after reverse shoulder arthroplasty (RSA) with stratification based on measurement method and implant design.

METHODS

This systematic review was performed using PRISMA-P guidelines. PubMed/Medline, Cochrane Trials, and Embase were queried for articles evaluating the relationship between humeral lengthening and clinical outcomes inclusive of range of motion (ROM), strength, outcome scores, and pertinent complications (acromial and scapular spine fractures, nerve injury) after RSA. The relationship between humeral lengthening and clinical outcomes was reported descriptively overall and stratified by measurement method and implant design (globally medialized vs. lateralized). A positive association was defined as increased humeral lengthening being associated with greater ROM, outcome scores, or a greater incidence of complications, whereas a negative association denoted that increased humeral lengthening was associated with poorer ROM, outcome scores, or a lower incidence of complications. Meta-analysis was performed to compare humeral lengthening between patients with and without fractures of the acromion or scapular spine.

RESULTS

Twenty-two studies were included. Humeral lengthening was assessed as the acromiohumeral distance (AHD), the distance from the acromion to the greater tuberosity (AGT), the acromion to the deltoid tuberosity (ADT), and the acromion to the distal humerus (ADH). Of 11 studies that assessed forward elevation, a positive association with humeral lengthening was found in 6, a negative association was found in 1, and 4 studies reported no association. Of studies assessing internal rotation (n = 9), external rotation (n = 7), and abduction (n = 4), all either identified a positive or lack of association with humeral lengthening. Studies assessing outcome scores (n = 11) found either a positive (n = 5) or no (n = 6) association with humeral lengthening. Of the studies that assessed fractures of the acromion and/or scapular spine (n = 6), 2 identified a positive association with humeral lengthening, 1 identified a negative association, and 3 identified no association. The single study that assessed the incidence of nerve injury identified a positive association with humeral lengthening. Meta-analysis was possible for AGT (n = 2) and AHD (n = 2); greater humeral lengthening was found in patients with fractures for studies using the AGT (mean difference 4.5 mm, 95% CI 0.7-8.3) but not the AHD. Limited study inclusion and heterogeneity prohibited identification of trends based on method of measuring humeral lengthening and implant design.

CONCLUSION

The relationship between humeral lengthening and clinical outcomes after RSA remains unclear and requires future investigation using a standardized assessment method.

Preoperative Planning for Reverse Shoulder Arthroplasty: Does the Clinical Range of Motion Match the Planned 3D Humeral Displacement?

INTRODUCTION

The functional outcome after reverse shoulder arthroplasty (RSA) is closely linked to how much the humerus shifts because of the implants. While two-dimensional (2D) angle measurements have been used to capture this shift, it can be measured in three dimensions (3D) as the arm change position (ACP). In a previous study, the ACP was measured using 3D preoperative planning software with the passive virtual shoulder range of motion obtained after RSA. The main objective of this study was to evaluate the relationship between the ACP and the actual active shoulder range of motion measured after RSA. The hypothesis was that the ACP and the active clinical range of motion are related such that the ACP is a reliable parameter to guide the preoperative planning of an RSA. The secondary objective was to assess the relationship between 2D and 3D humeral displacement measurements.

MATERIALS AND METHODS

This prospective observational study enrolled 12 patients who underwent RSA and had a minimum follow-up of 2 years. The active range of motion in shoulder flexion, abduction, and internal and external rotation was measured. At the same time, ACP measurements were taken from a reconstructed postoperative CT scan, in addition to the radiographic measurements of humeral lateralization and distalization angles on AP views in neutral rotation.

RESULTS

The mean humeral distalization induced by RSA was 33.3 mm (±3.8 mm). A non-statistically significant increase in shoulder flexion was observed for humeral distalization beyond 38 mm (R² = 0.29, p = 0.07). This "threshold" effect of humeral distalization was also observed for the gains in abduction, as well as internal and external rotations, which seemed better with less than 38 mm or even 35 mm distalization. No statistical correlation was found between the 3D ACP measurements and 2D angle measurements.

CONCLUSION

Excessive humeral distalization seems to be detrimental to joint mobility, especially shoulder flexion. Humeral lateralization and humeral anteriorization measured using the ACP seem to promote better shoulder range of motion, with no threshold effect. These findings could be evidence of tension in the soft tissues around the shoulder joint, which should be taken into consideration during preoperative planning.

How common is nerve injury after reverse shoulder arthroplasty? A systematic review

BACKGROUND

Nerve injury following reverse shoulder arthroplasty (RSA) is a known risk factor with wide ranging incidences reported. This systematic review evaluates the overall incidence of nerve injury following primary and revision RSA and summarizes the characteristics of the nerve injuries reported in the current literature.

METHODS

A systematic review was performed using separate database searches (Pubmed, Embase, Web of Science, Cochrane) following the PRISMA guidelines. Search criteria included the title terms "reverse shoulder," "reverse total shoulder," "inverted shoulder," and "inverted total shoulder" with publication dates ranging from 01/01/2010 to 01/01/2022. Studies that reported neurological injuries and complications were included and evaluated for primary RSA, revision RSA, number of nerve injuries, and which nerves were affected.

RESULTS

After exclusion, our systematic review consisted of 188 articles. A total of 40,146 patients were included, with 65% female. The weighted mean age was 70.3 years. The weighted mean follow-up was 35.4 months. The rate of nerve injury after RSA was 1.3% (510 of 40,146 RSAs). The rate of injury was greater in revision RSA compared to primary RSA (2.4% vs. 1.3%). Nerve injury was most common in RSAs done for a primary diagnosis of acute proximal humerus fracture (4.0%), followed by cuff tear arthropathy (3.0%), DJD (2.6%), and inflammatory arthritis (1.7%). Massive rotator cuff tears and post-traumatic arthritis cases had the lowest nerve injury rates (1.0% and 1.4%, respectively). The axillary nerve was the most commonly reported nerve that was injured in both primary and revision RSA (0.6%), followed by the ulnar nerve (0.26%) and median nerve (0.23%). Brachial plexus injury was reported in 0.19% of overall RSA cases.

CONCLUSION

Based on current English literature, nerve injuries occur at a rate of 1.3% after primary RSA compared with 2.4% after revision RSA. The most common nerve injury was to the axillary nerve (0.64%), with the most common operative diagnosis associated with nerve injury after RSA being acute proximal humerus fracture (4.0%). Surgeons should carefully counsel patients prior to surgery regarding the risk of nerve injury.

Influence of humeral lengthening on clinical outcomes in reverse shoulder arthroplasty

BACKGROUND

Deltoid tensioning secondary to humeral lengthening after reverse shoulder arthroplasty (RSA) is commonly theorized to be crucial to improving range of motion (ROM) but may predispose patients to acromial/scapular spine fractures and neurologic injury. Clinical evidence linking patient outcomes to humeral lengthening is limited. This study assesses the relationship between humeral lengthening and clinical outcomes after RSA.

METHODS

A single institution review of 284 RSAs performed in 265 patients was performed. Humeral lengthening was defined as the difference in the subacromial height preoperatively to postoperatively as measured on Grashey radiographs. The subacromial height was measured as the vertical difference between the most inferolateral aspect of the acromion and the most superior aspect of the greater tuberosity. The relationship between humeral lengthening and clinical outcomes was assessed on a continuous basis. Secondarily, clinical outcomes were assessed using a dichotomous definition of humeral lengthening (≤25 vs. >25mm) based on prior clinical and biomechanical work purporting a correlation with clinical outcomes. Improvement exceeding the minimal clinically important difference (MCID) and substantial clinical benefit (SCB) for ROM and outcome scores after RSA were also compared.

RESULTS

Humeral lengthening demonstrated a nonlinear relationship with postoperative ROM, clinical outcome scores, and shoulder strength and their improvement preoperatively to postoperatively. Furthermore, there were minimal differences in ROM measures, outcome scores, and shoulder strength when stratified using the dichotomous definition of humeral lengthening. No difference in the proportion of patients exceeding the MCID or SCB when stratified by humeral lengthening ≤25 vs. >25mm was found. There was no difference in humeral lengthening in patients with versus without complications.

CONCLUSION

No clear relationship between humeral lengthening and clinical outcomes was identified. The previously purported 25mm threshold for humeral lengthening did not predict improved patient outcomes. Outcomes after RSA are multifactorial; the relationship between humeral lengthening and outcomes is likely confounded by other patient and surgical factors.

LEVEL OF EVIDENCE

IV; Case Series.

The arm change position: Additional information for optimizing range of motion after reverse shoulder arthroplasty

INTRODUCTION

The arm change position (ACP) is a new parameter for evaluating the humerus' 3D displacement following reverse shoulder arthroplasty (RSA) during 3D pre operative planning. The purpose of this study was to analyze the relationship between ACP variations after RSA and simulated passive joint mobility. The assumption is that the ACP will to help optimize the passive joint mobility of a RSA implant.

METHODS

In 30 degenerative shoulders, four shoulder surgeons planned a RSA with virtual motion analysis. After this analysis, each plan was revised to optimize the range of motion. Relationships between the differences in movement amplitude and the differences in ACP were evaluated.

RESULTS

Arm lengthening and humerus lateralization were significantly associated with better joint mobility in all three planes (frontal, sagittal and axial). They were equally important for improving external rotation, extension, flexion and adduction. Anterior displacement of the humerus improved both internal and external rotation.

DISCUSSION

The ACP is a useful preoperative planning parameter for RSA. It could help with selecting the best implant combination, as well as determining their position, in order to optimize the simulated passive mobility relative to humerus displacement after RSA. To validate the value of the ACP in clinical practice, a prospective study is needed in which the postoperative joint mobility is measured in vivo as a function of the ACP.

LEVEL OF EVIDENCE

III, case control study.

Elongation of the brachial plexus after reverse shoulder arthroplasty: an anatomical study

INTRODUCTION

The use of reverse shoulder arthroplasty (RSA) is becoming more extended and its clinical results are good or excellent according to the literature. The main biomechanical characteristic of RSA is that it lowers and medializes the centre of rotation of the shoulder causing an arm lengthening. Although the number of neurological complications is low (5%), there are more neurophysiological changes in the brachial plexus with RSA than with the anatomic shoulder arthroplasty. The main goal of this study was to quantify the lengthening of the terminal branches of the brachial plexus suffered after RSA implantation.

MATERIALS AND METHODS

20 Embalmed cadavers were analysed. Four distances using bone references were employed to measure the lengthening of the arm and subacromial space. The brachial plexus and its terminal branches (radial, axillary, ulnar, musculocutaneous and median nerves) and the axillary artery, were identified and marked. Measurements were made to determine the change of position of the neurovascular structures, the arm lengthening and the lengthening of each nerve before and after the implantation of RSA. Two models of RSA were used: SMR^®(Lima) and Delta Xtend^®(DePuy-Synthes).

RESULTS

The mean arm elongation was 10.5 mm. The subacromial space suffers an elongation of 20.5-29.8%. All the neurovascular structures suffered elongation: median nerve 23.1%, musculocutaneous nerve 22.1%, ulnar nerve 19%, radial nerve 17%, axillary nerve 12-14.5%, axillary artery 24.8%. There were no differences in the results between the types of prosthesis.

CONCLUSIONS

Due to its design, the RSA causes an arm lengthening which is reflected by the elongation of the neurovascular structures of the arm.

Factors Influencing Acromial and Scapular Spine Strain after Reverse Total Shoulder Arthroplasty: A Systematic Review of Biomechanical Studies

BACKGROUND

Acromial and scapular spine fractures after reverse total shoulder arthroplasty (RTSA) can be devastating complications leading to substantial functional impairments. The purpose of this study was to review factors associated with increased acromial and scapular spine strain after RTSA from a biomechanical standpoint.

METHODS

A systematic review of the literature was conducted based on PRISMA guidelines. PubMed, Embase, OVID Medline, and CENTRAL databases were searched and strict inclusion and exclusion criteria were applied. Each article was assessed using the modified Downs and Black checklist to appraise the quality of included studies. Study selection, extraction of data, and assessment of methodological quality were carried out independently by two of the authors. Only biomechanical studies were considered.

RESULTS

Six biomechanical studies evaluated factors associated with increased acromial and scapular spine strain and stress. Significant increases in acromial and scapular spine strain were found with increasing lateralization of the glenosphere in four of the included studies. In two studies, glenosphere inferiorization consistently reduced acromial strain. The results concerning humeral lateralization were variable between four studies. Humeral component neck-shaft angle had no significant effect on acromial strain as analysed in one study. One study showed that scapular spine strain was significantly increased with a more posteriorly oriented acromion (55° vs. 43°; p < 0.001). Another study showed that the transection of the coracoacromial ligament increased scapular spine strain in all abduction angles (p < 0.05).

CONCLUSIONS

Glenoid lateralization was consistently associated with increased acromial and scapular spine strain, whereas inferiorization of the glenosphere reduced strain in the biomechanical studies analysed in this systematic review. Humeral-sided lateralization may increase or decrease acromial or scapular spine strain. Independent of different design parameters, the transection of the coracoacromial ligament resulted in significantly increased strains and scapular spine strains were also increased when the acromion was more posteriorly oriented. The results found in this systematic review of biomechanical in-silico and in-vitro studies may help in the surgical planning of RTSA to mitigate complications associated with acromion and scapular spine fracture.

Problems, complications, and reinterventions in 4893 onlay humeral lateralized reverse shoulder arthroplasties, a systematic review: part II-problems and reinterventions

BACKGROUND

Several modifications to the original Grammont reverse shoulder arthroplasty (RSA) design have been proposed to prevent distinctive issues, such as both glenoid and humeral lateralization. The aim of this systematic review was to determine rates of problems, complications, reoperations, and revisions after onlay lateralized humeral stem RSA, hypothesizing that these are design related.

METHODS

This systematic review was performed in accordance with the PRISMA statement guidelines. A literature search was conducted (1 January 2000 to 14 April 2020) using PubMed, Cochrane Reviews, Scopus, and Google Scholar, employing several combinations of keywords: "reverse shoulder arthroplasty," "reverse shoulder prosthesis," "inverse shoulder arthroplasty," "inverse shoulder prosthesis," "problems," "complications," "results," "outcomes," "reoperation," and "revision."

RESULTS

Thirty-one studies with 4893 RSA met inclusion criteria. The 892 postoperative problems and 296 postoperative complications represented overall problem and complication rates of 22.7% and 7.5%, respectively. Forty-one reoperations and 63 revisions resulted, with overall reoperation and revision rates of 1.7% and 2.6%, respectively.

CONCLUSIONS

Problem, complication, and reintervention rates proved acceptable when implanting a high humeral lateralization stem RSA. The most frequent problem was scapular notching (12.6%), and the most common postoperative complication was scapular stress fracture (1.8%). An overall humeral complication rate of 1.9% was identified, whereas no humeral fractures or stem loosening were reported with short stems. Infections (1.3%) were the most common reason for component revision, followed by instability (0.8%).

LEVEL OF EVIDENCE

Systematic review IV.

Early restoration of shoulder function in patients with the Grammont prosthesis compared to lateralized humeral design in reverse shoulder arthroplasty

BACKGROUND

This study aimed to compare the clinical outcomes and radiographic parameters of patients after reverse shoulder arthroplasty (RSA) between the Grammont prosthesis and lateralized humeral design prosthesis.

METHODS

A total of 114 patients who underwent RSA with a lateralized humeral design (group L; 71 shoulders) and medialized humeral design (group M; 43 shoulders) prosthesis for cuff tear arthropathy or irreparable rotator cuff tear were enrolled. Clinical outcomes including visual analog scale (VAS), American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES), and Constant scores and range of motion (ROM) were serially followed up at postoperative 3, 6, 12, and 24 months. Radiographic parameters were measured to evaluate preoperative and postoperative status.

RESULTS

Both prostheses demonstrated similar clinical outcomes and shoulder function preoperatively and at postoperative 2 years (P >.05). However, patients in group M had significantly better postoperative active forward flexion (postoperative 3 months, 115° ± 12° vs. 101° ± 14°; P <.001; 6 months, 125° ± 13° vs. 118° ± 13°; P <.013) and abduction (3 months, 105° ± 12° vs. 98° ± 12°; P = .002); VAS (3 months, 3.1 ± 1.2 vs. 3.7 ± 1.4; P = .031; 6 months, 2.3 ± 1.1 vs. 2.8 ± 1.3; P = .038); ASES (3 months, 64.2 ± 7.0 vs. 60.4 ± 9.2; P = .022; 6 months, 70.6 ± 6.0 vs. 66.6 ± 8.1; P = .007); and Constant scores (6 months, 59.6 ± 6.9 vs. 55.7 ± 9.3; P = .020). Group L showed a significantly lower rate of scapular notching than group M (15.5% vs. 41.8%; P < .001). The position of the proximal humerus in group L was more lateralized and less distalized than in group M after RSA.

CONCLUSIONS

RSA with both the Grammont and lateralized humeral design prostheses provided similar shoulder ROM restoration and functional improvements at a minimum of 2 years. However, patients with a humeral lateralized prosthesis showed slower recovery of shoulder function and ROM up to postoperative 6 months despite a lower incidence of scapular notching.

Similar optimal distalization and lateralization angles can be achieved with different reverse shoulder arthroplasty implant designs

Background

Optimal postoperative distalization (DSA) and lateralization (LSA) shoulder angles have been described as radiological measurements correlated with function after reverse shoulder arthroplasty (RSA). The proposed optimal values are DSA between 40° and 65° and LSA between 75° and 95°; however, whether these values can be reached with different implant designs is unclear.

Aim

To determine which RSA implant could achieve higher rates of optimal DSA and LSA, to determine any association between each implant and optimal DSA and LSA, and to assess the correlation of the preoperative critical shoulder angle (CSA) and acromial index (AI) with the DSA and LSA.

Methods

This was a retrospective comparative study of all patients who underwent primary RSA for rotator cuff arthropathy. Three RSA implant designs were included, based on which patients were divided into three groups: group 1 (FH Arrow™; 16 patients) comprised onlay implants with a 135° neck-shaft angle (NSA); group 2 (Biomet Comprehensive™; 20 patients) comprised onlay implants with a 147° NSA; group 3 (Mathys Affinis™; 15 patients) comprised inlay implants with a 155° NSA. The AI and CSA were measured on preoperative radiographs. The DSA and LSA were measured on true AP postoperative radiographs.

Results

The mean DSAs were 44°, 46°, and 46° (P = 0.671) and the mean LSAs were 92°, 91°, and 82° for groups 1, 2, and 3, respectively (P = 0.003). Group 3 had lower LSA than groups 1 (-10°; P = 0.005) and 2 (-9°; P = 0.002). Optimal DSA and LSA were achieved in 71% and 73% of all arthroplasties, respectively. No association between implant designs and achieving an optimal DSA or LSA was observed. None of the implant designs had DSA >65°. The most common cause of failure to reach an optimal LSA in onlay implants was a combination of LSA >95° and DSA <40°. The most common cause of failure in group 3 was DSA <40°. The DSA was negatively correlated with the AI (-0.384; P = 0.006) and CSA (-0.305; P = 0.033). No correlation was observed between the LSA and AI (P = 0.312) or CSA (P = 0.137).

Conclusion

The LSA is lower with the Mathys Affinis™ implant than with the Biomet Comprehensive™ and FH Arrow™ implants; however, most LSAs are in the optimal ranges, and no association is observed between different implant designs and optimal DSA and LSA. Implant design, CSA, and AI should be considered during preoperative planning to achieve optimal DSA and LSA.

Problems, complications, and reinterventions in 4893 onlay humeral lateralized reverse shoulder arthroplasties: a systematic review (part I-complications)

Background

Several modifications to the original Grammont reverse shoulder arthroplasty (RSA) design have been proposed to prevent distinctive issues, such as both glenoid and humeral lateralization. The aim of this systematic review was to determine rates of problems, complications, reoperations, and revisions after onlay lateralized humeral stem RSA, hypothesizing that these are design related.

Methods

This systematic review was performed in accordance with the PRISMA statement guidelines. A literature search was conducted (01.01.2000–14.04.2020) using PubMed, Cochrane Reviews, Scopus, and Google Scholar employing several combinations of keywords: “reverse shoulder arthroplasty,” “reverse shoulder prosthesis,” “inverse shoulder arthroplasty,” “inverse shoulder prosthesis,” “problems,” “complications,” “results,” “outcomes,” “reoperation,” “revision.”

Results

Thirty-one studies with 4893 RSA met inclusion criteria. The 892 postoperative problems and 296 postoperative complications represented overall problem and complication rates of 22.7% and 7.5%, respectively. Forty-one reoperations and 63 revisions resulted, with an overall reoperation rate of 1.7% and overall revision rate of 2.6%.

Conclusions

Problem, complication, and reintervention rates proved acceptable when implanting a high humeral lateralization stem in RSA. The most frequent problem was scapular notching (12.6%), and the most common postoperative complication was scapular stress fracture (1.8%). An overall humeral complication rate of 1.9% was identified, whereas short stems reported no humeral fractures or stem loosening. Infections (1.3%) proved to be the most common reason for component revision, and instability had a complication rate of 0.8%.

Level of evidence

Systematic review IV

Acromion and Scapular Spine Fractures Following Reverse Total Shoulder Arthroplasty

Reverse total shoulder arthroplasty (RSA) continues to see tremendous growth as the indications have expanded. A variety of complications have been described, including fractures of the acromion or scapular spine. These fractures are painful and can compromise shoulder stability and functional outcomes following RSA. Multiple studies have recently investigated the incidence, risk factors, and treatment strategies for these injuries. In this article, the authors review current literature and discuss the incidence, cause, associated risk factors, treatment options, and outcomes following fractures of the acromion or scapular spine after RSA.

Patient risk factors for acromial stress fractures after reverse shoulder arthroplasty: a multicenter study

BACKGROUND

Despite the growing recognition of acromial stress fractures (ASFs) after reverse total shoulder arthroplasty (RTSA), most of the current data are derived from single-center studies with limited generalizability. This multicenter study investigated the incidence of ASFs after RTSA and identified preoperative patient characteristics associated with their occurrence.

METHODS

Using 2 institutional registries from different regions of the United States, we identified 1479 patients undergoing either primary or revision RTSA between 2013 and 2018 with minimum 3-month follow-up. ASFs were defined as radiographic evidence of an acromial or scapular spine fracture with clinical symptoms (eg, tenderness over the acromion or scapular spine). Multivariable logistic regression was performed to identify preoperative patient factors associated with the development of ASFs.

RESULTS

Overall, 54 (3.7%) patients were diagnosed with an ASF after RTSA. Patient-related factors independently associated with the development of an ASF included female sex (odds ratio [OR], 2.21 reference: male; 95% confidence interval [CI], 1.03-4.74; P < .05), rheumatoid arthritis (OR, 2.30; 95% CI, 1.02-5.16; P < .05), osteoporosis (OR, 2.55; 95% CI, 1.24-5.21; P < .05), a diagnosis of degenerative joint disease with rotator cuff tear (OR, 4.74 reference: degenerative joint disease without rotator cuff tear; 95% CI, 1.84-12.23; P < .05), and fracture malunion/nonunion (OR, 5.21; 95% CI, 1.20-22.76; P < .05).

CONCLUSIONS

The non-negligible percentage of ASFs that occur after RTSA is associated with the diagnoses of rotator cuff dysfunction and chronic fracture sequelae in female patients with suboptimal bone health. This information can be used to counsel patients and set expectations about potential setbacks in recovery.

Infraspinatus and deltoid length and patient height: implications for lateralization and distalization in reverse total shoulder arthroplasty

BACKGROUND

Restoration of muscular strength is predicated on restoration of muscle length. The purpose of this study was to describe infraspinatus and deltoid length preoperative to reverse total shoulder arthroplasty (RTSA) to guide distalization and lateralization to restore preoperative muscle length.

METHODS

This was a retrospective radiographic study. We measured the infraspinatus length on preoperative computed tomographic images and the deltoid length on preoperative radiographs. For all measurements, reliability was first established by comparing measurements between 2 observers, and intraclass correlation coefficients (ICCs) were calculated. We then calculated descriptive statistics for these muscle lengths and developed a formula to predict these muscle lengths from patient demographics.

RESULTS

We measured infraspinatus length in 97 patients and deltoid length in 108 patients. Inter-rater reliability was excellent, with all ICCs >0.886. The mean infraspinatus length was 15.5 cm (standard deviation 1.3) and ranged from 12.6-18.9 cm, whereas the deltoid length was 16.2±1.7 cm and ranged from 12.5-20.2 cm. Both infraspinatus (r = 0.775, P < .001) and deltoid length (r = 0.717, P < .001) were highly correlated with patient height but did not differ between diagnoses. Formulae developed through linear regression allowed prediction of muscle length to within 1 cm in 78% and within 2 cm in 100% for the infraspinatus and 60% and 88% for the deltoid.

CONCLUSION

Deltoid and infraspinatus length are variable but highly correlated with patient height. To maintain tension, 2 mm of lateralization and distalization should be added for every 6 inches (∼15 cm) of height above average for a Grammont-style RTSA.

Complications of reverse shoulder arthroplasty: a concise review

Reverse shoulder arthroplasty is an ideal treatment for glenohumeral dysfunction due to cuff tear arthropathy. As the number of patients treated with reverse shoulder arthroplasty is increasing, the incidence of complications after this procedure also is increasing. The rate of complications in reverse shoulder arthroplasty was reported to be 15%-24%. Recently, the following complications have been reported in order of frequency: periprosthetic infection, dislocation, periprosthetic fracture, neurologic injury, scapular notching, acromion or scapular spine fracture, and aseptic loosening of prosthesis. However, the overall complication rate has varied across studies because of different prosthesis used, improvement of implant and surgical skills, and different definitions of complications. Some authors included complications that affect the clinical outcomes of the surgery, while others reported minor complications that do not affect the clinical outcomes such as minor reversible neurologic deficit or minimal scapular notching. This review article summarizes the processes related to diagnosis and treatment of complications after reverse shoulder arthroplasty with the aim of helping clinicians reduce complications and perform appropriate procedures if/when complications occur.

Adjusting Implant Size and Position Can Improve Internal Rotation After Reverse Total Shoulder Arthroplasty in a Three-dimensional Computational Model

BACKGROUND

Efforts during reverse total shoulder arthroplasty (RSA) have typically focused on maximizing ROM in elevation and external rotation and avoiding scapular notching. Improving internal rotation (IR) is often overlooked, despite its importance for functional outcomes in terms of patient self-care and hygiene. Although determinants of IR are multifactorial, it is unable to surpass limits of bony impingement of the implant. Identifying implant configurations that can reduce bony impingement in a computer model will help surgeons during preoperative planning and also direct implant design and clinical research going forward.

QUESTIONS/PURPOSES

In a CT-modeling study, we asked: What reverse total shoulder arthroplasty implant position improves the range of impingement free internal rotation without compromising other motions (external rotation and extension)?

METHODS

CT images stored in a deidentified teaching database from 25 consecutive patients with Walch A1 glenoids underwent three-dimensional templating for RSA. Each template used the same implant and configuration, which consisted of an onlay humeral design and a 36-mm standard glenosphere. The resulting constructs were virtually taken through ROM until bony impingement was found. Variations were made in the RSA parameters of baseplate lateralization, glenosphere size, glenosphere overhang, humeral version, and humeral neck-shaft angle. Simulated ROM was repeated after each parameter was changed individually and then again after combining multiple changes into a single configuration. The impingement-free IR was calculated and compared between groups. We also evaluated the effect on other ROM including external rotation and extension to ensure that configurations with improvements in IR were not associated with losses in other areas.

RESULTS

Combining lateralization, inferiorization, varus neck-shaft angle, increased glenosphere size, and increased humeral anteversion resulted in a greater improvement in internal rotation than any single parameter change did (median baseline IR: 85° [interquartile range 73° to 90°]; combined changes: 119° [IQR 113° to 121°], median difference: 37° [IQR 32° to 43°]; p < 0.001).

CONCLUSION

Increased glenosphere overhang, varus neck-shaft angle, and humeral anteversion improved internal rotation in a computational model, while glenoid lateralization alone did not. Combining these techniques led to the greatest improvement in IR.

CLINICAL RELEVANCE

This computer model study showed that various implant changes including inferiorization, varus neck-shaft angle, increased glenosphere size, and increased humeral anteversion can be combined to increase impingement-free IR. Surgeons can employ these currently available implant configurations to improve IR when planning and performing RSA. These findings support the need for further clinical studies validating the effect of implant configuration on resultant IR.

An Evolution of Shoulder Periprosthetic Infections Management: MicroDTTect, Bioactive Glass and Tantalum Cones Employment

Periprosthetic joint infections of the shoulder (PJIS) are the major cause for revision within the first two post-operative years, and are challenging both to diagnose and treat. Success depends on early identification of microorganisms, appropriate surgical procedures and efficient antibiotic administration. The peculiar microbiology of the shoulder may render the criteria for hip/knee PJI management inappropriate. In addition, later cases with clinically subtle signs often present diagnostic challenges. In recent years, specific issues of PJIS have been managed through the use of new instruments, such as MicroDTTect in pathogen detection and Bioactive Glass and tantalum cones in humeral bone loss. In the literature to date, no reports have been found that discuss the application in shoulder revisions and infections. The early identification of the microorganisms that cause infection may help improve both treatment strategies and the efficacy of therapy. MicroDTTect proved to be more efficient than swab collection for bacterial identification in orthopedic surgery, thus reducing analysis costs. The increasing number of shoulder arthroplasties is associated with an increase in the number of revisions. In cases of massive metaphyseal humeral bone loss, several techniques have been described; no reports have been reported regarding tantalum in humeral bone loss management. In some cases the tantalum cones required adaptation for femoral diaphysis in the augmentation of the humerus metaphysis and bone loss management improvement. Obtaining stable osseointegration of prosthetic implants is one of the greatest issues in orthopedic surgery, and even more crucial in revisions. Bioactive glasses demonstrated good regenerative and osseointegration properties, and an excellent candidate as a bone graft, scaffold and antibiotics deliverer. The Bioactive glasses were used to increase prosthesis-bone interface stability and fill bone defects in PJIS revision surgeries, contributing to the prevention of re-infection. Longer-term follow-up will be necessary to determine if construction durability is improved in the long term.

Influence of implant design and parasagittal acromial morphology on acromial and scapular spine strain after reverse total shoulder arthroplasty: a cadaveric and computer-based biomechanical analysis

BACKGROUND

The purpose was to analyze the influence of deltoid lengthening due to different implant designs and anatomic variations of the acromion and scapular spine (SS) in the parasagittal plane on strain patterns after reverse shoulder arthroplasty (RSA).

METHODS

Ten cadaveric shoulders with strain rosettes placed on the surface of the acromial body (Levy II) and SS (Levy III) were tested using a shoulder simulator. RSA using humeral onlay (+3, +5, +8, +10, +13 mm) and glenosphere lateralization (0, +6 mm) was performed. Arm lengthening and magnitude of strain on acromion/SS were measured. The length of deltoid was assessed using validated computer modeling. Anatomic variance of the SS angle and position of acromion in relation to the scapular plane was examined. For comparison of strain as a function of deltoid lengthening, 25 mm was used as a threshold value for comparison based on previous literature demonstrating a decrease in Constant score and active anterior elevation in patients with arm lengthening >25 mm.

RESULTS

At maximal deltoid lengthening (30.8 mm), average strains were 1112 με (acromion) and 1165 με (SS) (P < .01). There was an 82.6% increase in acromial strain at maximum lengthening compared with 25 mm (P = .02) and a strain increase of 79 με/mm deltoid lengthening above a threshold of 25 mm. The strain results delineated 2 anatomic groups: 5 of 10 specimens (group A) showed higher strain on SS (1445 με) vs. acromion (862 με, P = .02). Group A had a more posteriorly oriented acromion, whereas group B was anteriorly oriented (P < .001).

CONCLUSION

Deltoid lengthening above 25 mm produced large strains on the acromion/SS. Anatomic variation may indicate that as the acromion is more posteriorly oriented, the SS takes more strain from the deltoid vs. the acromion. Our study's data may help surgeons identify a high-risk population for increased strain patterns after RSA.

Onlay Uncemented Lateralized Reverse Shoulder Arthroplasty for Fracture Sequelae Type 1 with Valgus/Varus Malunion: Deltoid Lengthening and Outcomes

The successful treatment of proximal humeral fractures remains challenging for shoulder surgeons, and failure rates are high, regardless of initial treatment. This study aimed to analyze the clinical and radiographic midterm results of onlay lateralized cementless stem reverse shoulder arthroplasty (RSA) in patients with valgus/varus malunion proximal humerus fracture sequelae without metaphyseal osteotomy. We retrospectively studied 35 cases with the diagnosis of fracture sequelae of the proximal part of the humerus with valgus/varus malunion. The mean duration of follow-up was 4.6 years (range, 2 to 7 years), and the mean time between fracture and arthroplasty was 6 years (1 to 32 years). Seventeen patients (48.6%) had initially been treated nonoperatively. The Constant score (CS), active range of motion, and radiographs of the affected shoulders, as well as the acromion to greater tuberosity (AGT) distance and deltoid length (DL), were analyzed before surgery and at their latest follow-up. A total of thirty-three patients (94.3%) rated their outcome as very good or good. Mean CS, forward flexion, and external rotation improved significantly (p < 0.0001), as did internal rotation and pain (p < 0.05). AGT distance significantly increased postoperatively from 14.7 to 43.3 mm, as did DL from 143 to 170 mm (p < 0.05). There was no correlation between the outcomes and valgus/varus deformity, previous surgeries, or AGT distance/DL. A total of four complications occurred (11.4%): two dislocations were detected (5.7%) and successfully revised with a longer cemented stem. Onlay lateralized uncemented stem RSA improves clinical outcomes and decreases complications when treating valgus/varus malunion fracture sequelae, avoiding intraoperative technical challenges, such as tuberosities osteotomy conscious of bone loss and proper deltoid tensioning.

The modern reverse shoulder arthroplasty and an updated systematic review for each complication: part I

Background

Globally, reverse shoulder arthroplasty (RSA) has moved away from the Grammont design to modern prosthesis designs. The purpose of this 2-part study was to systematically review each of the most common complications of RSA, limiting each search to publications in 2010 or later. In this part (part I), we examined (1) scapular notching (SN), (2) periprosthetic infection (PJI), (3) mechanical failure (glenoid or humeral component), and (4) neurologic injury (NI).

Methods

Four separate PubMed database searches were performed following Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Overall, 113 studies on SN, 62 on PJI, 34 on mechanical failure, and 48 on NI were included in our reviews. Univariate analysis was performed with the χ² or Fisher exact test.

Results

The Grammont design had a higher SN rate vs. all other designs combined (42.5% vs. 12.3%, P < .001). The onlay humeral design had a lower rate than the lateralized glenoid design (10.5% vs. 14.8%, P < .001). The PJI rate was 2.4% for primary RSA and 2.6% for revision RSA. The incidence of glenoid and humeral component loosening was 2.3% and 1.4%, respectively. The Grammont design had an increased NI rate vs. all other designs combined (0.9% vs. 0.1%, P = .04).

Conclusions

Focused systematic reviews of the recent literature with a large volume of RSAs demonstrate that with the use of non-Grammont modern prosthesis designs, complications including SN, PJI, glenoid component loosening, and NI are significantly reduced compared with previous studies. As the indications for RSA continue to expand, it is imperative to accurately track the rates and types of complications to justify its cost and increased indications.

Treatment of cephalotuberosity fractures in elderly patients treated by reverse shoulder prosthesis: a study of functional results in relation to deltoid tension

INTRODUCTION

The treatment of proximal humerus fractures is a therapeutic challenge in the elderly as the functional demands of these patients are high. We postulated that there may be a relationship between functional results and deltoid tension when these fractures are treated with a reverse prosthesis. This study was performed to determine the optimal tension of the deltoid. The primary outcome was the constant score in relation to humeral length at the final follow-up.

MATERIALS AND METHODS

Our retrospective cohort consisted of 45 patients treated with a reverse fracture prosthesis during the period from January 2010 to July 2017. The fractures were all classified as Neer III or IV, 91% of our patients were women and the average age was 82 years.

RESULTS

Constant score and antepulsion were improved with humeral elongation between 10 and 25 mm (p < 0.02 and p < 0.05, respectively). External rotation was improved with humeral elongation (p < 0.03).

CONCLUSION

Tuberosity reinsertion improves mobility in patients treated surgically for a reverse fracture prosthesis. The recovery of anatomical retroversion seems of fundamental importance, and we confirmed that deltoid tension that must also be taken into account to improve functional results of reverse shoulder prosthesis on fracture. The ideal humeral elongation seems to be between 10 and 25 mm, in relation to the contralateral side, to obtain better functional results.

Humeral Bone Loss in Revision Total Shoulder Arthroplasty: the Proximal Humeral Arthroplasty Revision Osseous inSufficiency (PHAROS) Classification System

BACKGROUND

Humeral bone loss is commonly encountered during revision shoulder arthroplasty and anticipating humeral bone defects can help the revision surgeon make appropriate plans to achieve adequate fixation and stability. No validated classification system exists to characterize humeral bone loss in the setting of revision shoulder arthroplasty.

QUESTIONS/PURPOSES

The purposes of this study were (1) to create a classification system for humeral bone loss in revision shoulder arthroplasty; (2) to determine the classification system's reliability; and (3) to determine whether humeral bone loss type is associated with intraoperative humeral-related reconstruction characteristics.

METHODS

This was a comparative retrospective radiographic study. First, six surgeons from five centers collaborated to create a classification by consensus. Second, two surgeons from two other centers who had fellowship training in shoulder and elbow surgery, who were blinded to each other's grades and all patient details other than plain radiographs, and who were not involved in creation of the system, classified true AP, AP, and lateral (axillary and/or scapular-Y) radiographs from 108 revision (413 radiographs) from one center that were performed between November 15, 2006, and January 4, 2018. Interobserver reliability was calculated by comparing those two reviews and determining Cohen's κ. In addition, one reviewer repeated his assessments twice, 4 months apart, to determine intraobserver reliability using Cohen's κ. Third, we performed a retrospective chart study of these same revisions to determine intraoperative humeral-related reconstruction characteristics such as the use of greater tuberosity fixation, stem length, humeral bone grafting, and the use of proximal humeral replacement or total humeral replacement; at the center where these revisions were performed during that timespan, no attempt to classify bone loss was made. During that period, the general indications for greater tuberosity fixation included the absence of a stable osseous connection between the greater tuberosity and the shaft of the humerus with a tuberosity amendable to repair; the general indications for use of longer stems were inability to obtain a minimum of two cortical widths of overlap between the implant and the humeral diaphysis and/or loss of the greater tuberosity; and the general indications for proximal and total humeral replacement were bone loss that was felt to be too severe to allow reconstruction with allograft.

RESULTS

The classification system consists of three types of humeral bone loss: Type 1 is loss of the epiphysis with subtypes for loss of the calcar and loss of the greater tuberosity; Type 2 is loss of the metadiaphysis above the deltoid attachment with a subtype for cortical thinning; and Type 3 is bone loss extending below the deltoid attachment with a subtype for cortical thinning. We studied 108 revisions: 38 (35%) without bone loss, 34 (31%) Type 1, 27 (25%) Type 2, and nine (8%) Type 3. For reliability, interrater κ was 0.545 and in 71% (77 of 108) of revisions, the two raters agreed on a numeric type. Intrarater κ was 0.615 and in 77% (83 of 108) of revisions, the rater agreed with himself as to the numeric type. Stem length increased with class type (Type 1 median [range] 130 [70-210], Type 2 150 [70-210], Type 3 190 [70-240], p = 0.005). Most greater tuberosity fixation for intraoperative fracture was in Types 1 and 2 (13 of 18 compared with the five of 18 of greater tuberosity fixation that was within Types 0 and 3, p = 0.043). Most bone grafting was in Types 2 and 3 (eight of 13 compared with five of 13 of bone grafting was in Types 0 and 1, p = 0.044). Most proximal humeral and total humeral replacements were in Type 3 (three of four compared with one of four, p < 0.001).

CONCLUSIONS

We developed the Proximal Humeral Arthroplasty Revision Osseous inSufficiency (PHAROS) system, which has adequate, if imperfect, reliability to classify humeral bone loss in the setting of revision shoulder arthroplasty. This classification system may be useful to anticipate the complexity of humeral reconstruction. Further validation incorporating advanced imaging and further evaluators will be necessary.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Grammont Award 2018: Scapular fractures in reverse shoulder arthroplasty (Grammont style): prevalence, functional, and radiographic results with minimum 5-year follow-up

BACKGROUND

Scapular fractures after reverse shoulder arthroplasty (RSA) are an increasingly reported complication. Information is missing regarding midterm to long-term follow-up consequences. The aim of this study was to determine the rate of scapular fracture (acromial base and spine) after Grammont-style RSA and to report functional and radiographic results of patients with a minimum 5-year follow-up.

MATERIALS AND METHODS

We retrospectively reviewed 1953 Grammont-style RSAs in 1745 patients in a multicenter study. Of these, 953 patients (1035 RSAs) had minimum 5-year follow-up for functional and radiographic assessment (anteroposterior and scapular Y views.

RESULTS

Twenty-six patients (1.3%) had sustained a scapular fracture; of these, 19 (10 acromial base and 9 spine fractures) had minimum 5-year follow-up and were reviewed at a mean follow-up of 97 months. Three patients (15.8%) were diagnosed at the last follow-up after an undiagnosed fracture. There were 3 traumatic cases (15.8%) and 13 (68.4%) without antecedent trauma. These 16 patients underwent nonoperative treatment. The fracture was healed in 8 (4 acromion and 4 spine). The average active forward elevation was 109° (range, 50°-170°), and the Constant score was 47.0 points (range, 8-81 points).

CONCLUSIONS

Scapular fractures after Grammont-style RSAs are rare (1.3%) but remain a concern. These fractures occur mainly in the early postoperative 6 months. Immobilization with an abduction splint frequently resulted in nonunion or malunion. Final functional outcomes are poor regardless of acromial or spine fracture compared with primary RSA without fracture.

Radiologic Comparison of Humeral Position according to the Implant Designs Following Reverse Shoulder Arthroplasty: Analysis between Medial Glenoid/Medial Humerus, Lateral Glenoid/Medial Humerus, and Medial Glenoid/Lateral Humerus Designs

Background

The currently available reverse shoulder arthroplasty (RSA) designs can be classified into medial glenoid/medial humerus (MGMH), lateral glenoid/medial humerus (LGMH), and medial glenoid/lateral humerus (MGLH) prosthesis designs. The purpose of this study was to radiologically analyze the effect of different RSA designs on humeral position following RSA.

Methods

A total of 50 patients who underwent primary RSA were retrospectively analyzed. Among 50 patients, 33 patients (group A: MGMH) underwent RSA with Aequalis system (Wright, Inc, Bloomington, MN, USA), 6 (group B: LGMH) with Aequalis system using bony increased offset, and 11 (group C: MGLH) with Aequalis Ascend Flex system. The acromiohumeral distance, acromioepiphyseal distance (AED), lateral humeral offset (LHO), LHO from the center of rotation (LHO^COR), and deltoid length were radiologically measured to quantify the distalization and lateralization of the humerus.

Results

The increment in postoperative AED was 19.92 ± 3.93 mm in group A, 24.52 ± 5.25 mm in group B, and 25.97 ± 5.29 mm in group C, respectively (p=0.001). The increment in postoperative LHO was 0.13 ± 6.30 mm, 8.00 ± 12.14 mm, and 7.42 ± 6.88 mm, respectively (p=0.005). The increment in postoperative LHO^COR was 20.76 ± 6.06 mm, 22.04 ± 5.15 mm, and 28.11 ± 4.14 mm, respectively (p=0.002).

Conclusions

The radiologic analysis of the effect of different RSA designs on humeral position following RSA showed significant differences in the increment in postoperative AED, LHO, and LHO^COR between the 3 groups. Therefore, MGLH design seems to be more effective for humeral distalization and lateralization compared to original Grammont design.

Geometric modification of the humeral position after total reverse shoulder arthroplasty: what is the optimal lowering of the humerus?

BACKGROUND

The main mechanical effect after reverse shoulder arthroplasty (RSA) is the lowering of the glenohumeral rotation center. The optimal value of the humeral lowering after RSA is still debated. The main objective of our study was to determine the lowering and medialization of the humerus and to correlate these parameters with short-term functional results.

MATERIALS AND METHODS

The study included 70 patients with complete radiographic and clinical data. A multivariate analysis was used to compare the clinical and radiographic outcomes with the humeral lowering.

RESULTS

The mean humeral lowering was 25.4 mm (range, 6-38 mm), and the mean medialization was 9.2 mm (range, 0-20 mm). Humeral lowering significantly influenced active forward elevation and the rate of scapular notching.

DISCUSSION

The best clinical results and the lowest incidence of scapular notching were found after a lowering of more than 24 mm in our series. We recommend humeral lengthening of at least 24 mm after implanting a total reverse shoulder prosthesis.

Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases

BACKGROUND

Scapular stress fractures after reverse shoulder arthroplasty (RSA) are a potentially serious complication with modern lateralized and onlay implants. The aim of this study was to report the scapular spine stress fracture rate after RSA with an onlay, 145° humeral stem, analyzing potential fracture risk factors and clinical outcomes in a large cohort of patients.

METHODS

A consecutive series of 485 RSAs were implanted with the Aequalis Ascend Flex stem. Data collection included preoperative and postoperative clinical and radiographic assessment findings (rotator cuff Goutallier grade; Hamada, Walch, and Favard classifications; range of motion; Constant score) and perioperative data. Patients with a scapular spine fracture following RSA were matched with nonfracture control patients, and preoperative variables were tested to determine whether they were predictive of a scapular spine fracture.

RESULTS

A scapular spine fracture following RSA occurred in 21 patients (4.3%), with a mean time to diagnosis of 8.6 months (range, 1-34 months). No preoperative factor was found to be a significant predictor of scapular spine fracture. Both groups showed significant improvements in active mobility measurements and Constant scores from preoperatively to final follow-up (P < .001). The control group scored significantly better than the scapular spine fracture group regarding the Constant score and forward flexion.

CONCLUSION

Scapular spine fractures have shown an increased prevalence after onlay-design RSA. This series was not able to link any clear risk factors. Functional results are limited, regardless of the fracture management.

The lateralization and distalization shoulder angles are important determinants of clinical outcomes in reverse shoulder arthroplasty

BACKGROUND

Reverse shoulder arthroplasty (RSA) designs vary in the lateralization and distalization geometry, which may affect functional outcomes. The purpose was to determine the effect of RSA lateralization and distalization on final functional outcomes by using the "lateralization shoulder angle" (LSA) and the "distalization shoulder angle" (DSA).

METHODS

Forty-six consecutive patients who underwent RSA for cuff tear arthropathy were retrospectively evaluated. Functional outcome and radiographs were evaluated at a minimum of 2 years postoperatively and compared between implants with or without glenoid lateralization and with or without humeral-sided lateralization. Anteroposterior shoulder radiographs were used to evaluate the LSA and DSA.

RESULTS

Both angles showed substantial to almost perfect intrarater and inter-rater agreement. Higher LSA values were found in more lateralized RSAs (P = .027), and values between 75° and 95° were correlated with better active external rotation (quadratic regression analysis R² = 0.553, P < .001). Postoperative active anterior elevation (R² = 0.2, P = .008), Constant (r_s = 0.29, P = .05), and Activities of Daily Living Requiring External Rotation scores (r_s = 0.4 P = .007) had a positive correlation with the LSA. The quadratic regression analysis also showed that a DSA between 40° and 65° resulted in better active anterior elevation (R² = 0.4, P < .001) and abduction (R² = 0.4, P < .001). The negative correlation between the LSA and DSA (r_s = -0.7, P < .001) revealed that, according to the implant used, the more distally the RSA is placed the less lateralization is achieved.

CONCLUSIONS

The LSA and the DSA are reproducible measurements that may be used to estimate "lateralization and distalization" after RSA. These measurements are correlated with postoperative clinical outcomes.