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PURPOSE: This study aimed to identify the demographic-, radiographic-, and surgery-related factors influencing postoperative functional internal rotation (fIR) following reverse total shoulder arthroplasty (RTSA). METHODS: In this retrospective cohort study, patients who underwent RTSA between June 2013 and April 2018 at a single institution were assigned to two groups ("IROgood" or "IRObad"). Patients were classified as having good fIR (≥8 points in the Constant-Murley score (CS) and fIR to the twelfth thoracic vertebra or higher) or poor fIR (≤2 points in the CS and fIR to the twelfth thoracic vertebra or lower) after RTSA with a single implant model. The minimum follow-up period was two years. Standardized shoulder-specific scores (Visual Analogue Scale (VAS), Simple Shoulder Test (SST), American Shoulder and Elbow Surgeons Score (ASES), Constant-Murley score (CS)) were used to assess the pre- and postoperative functional status of patients. Postoperative radiographic evaluation included the distalization shoulder angle (DSA), lateralization shoulder angle (LSA), critical shoulder angle (CSA), acromiohumeral distance (AHD), glenoid inclination (GI), medialization of the center of rotation (COR), lateralization of the humerus, and distalization of the greater tuberosity. Additionally, preoperative evaluation included rotator cuff arthropathy according to Hamada, glenoid version, anterior or posterior humeral head subluxation, and fatty infiltration of the rotator cuff according to Goutallier. Univariate analysis of demographic, surgical, radiographic, and implant-associated parameters was performed to identify factors associated with postoperative fIR. The Shapiro-Wilk test assessed the normal distribution of the data. Intergroup comparisons regarding demographic and surgery-related factors were conducted using the Mann-Whitney-U Test. Radiographic changes were compared using chi-square or Fisher's exact tests. The significance level was set at p < 0.05. RESULTS: Of a total of 42 patients, 17 (age: 73.7 ± 5.0 years, follow-up (FU) 38 months [IQR 29.5-57.5]) were included in the "IRObad" group, and 25 (age: 72 ± 6.1 years, FU 47 months [IQR 30.5-65.5]) were included in the "IROgood" group. All patients were treated with the same type of implant (glenosphere size: 36 mm, 14.3%; 39 mm, 38.1%; 42 mm, 47.6%; neck-shaft angle: 135° in 68.0%; 155° in 32.0%) and had comparable indications. Univariate analysis did not reveal any of the investigated demographic, radiographic, or surgery-related parameters as risk factors for poor postoperative fIR (p > 0.05). CONCLUSION: None of the investigated factors, including implant-associated parameters, influenced postoperative fIR after RTSA in this cohort.

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Background: Recently, the issue of subacromial notching, caused by acromial impingement has been reported. The purpose of this study was to assess the impact of differences in the distance between the glenosphere center and the greater tuberosity (DGT) and the distance between the glenosphere center and the acromion (DA) on the closest distance between the greater tuberosity and the acromion during active abduction in shoulders with reverse total shoulder arthroplasty (RSA). Methods: Eleven shoulders with semiinlay RSA were analyzed. Subjects underwent fluoroscopy during active scapular plane abduction. Computed tomography of their shoulders was performed to create three-dimensional (3D) implant models at a mean of 16 months after surgery. Using model-image registration techniques, poses of 3D implant models were iteratively adjusted to match their silhouettes with the silhouettes in the fluoroscopic images (shape matching), and 3D kinematics of implants were computed. The closest distance between the acromion and greater tuberosity was computed at maximum abduction. DA and DGT were measured from 3D surface models. Shoulders were divided into two groups based on DA and DGT measurements and their closest distance data were compared between the groups. Results: There were 7 shoulders with DA ≥ DGT, and 4 shoulders with DA < DGT. Shoulders with DA ≥ DGT showed a significantly wider distance between the greater tuberosity and acromion at maximum abduction compared to those with DA < DGT (5.9 ± 2.4 mm vs. 0.6 ± 0.7 mm, respectively, P = .0021). There were no significant differences in maximum glenohumeral abduction angle and humeral abduction angle between the two groups. Although DA was significantly greater in shoulders with DA ≥ DGT than in those with DA < DGT (43.7 ± 4.4 mm vs. 35.1 ± 6.7 mm, respectively, P = .0275), there was no significant difference in DGT between the two groups. Conclusion: When DGT is less than DA in shoulders with RSA, the closest distance between the greater tuberosity and the acromion at maximum abduction is significantly wider compared to cases where DGT is greater than DA by 3D measurement. Therefore, acromial impingement is less likely to occur in shoulders with RSA when DA is greater than DGT. To avoid acromial impingement, it might be important to make DA greater than DGT.

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Background: Despite the increasing use of revision reverse total shoulder arthroplasty (RTSA), studies directly comparing revision RTSA performed for different failed index procedures are limited. We therefore compared the results of revision RTSA between patients with a failed primary anatomic arthroplasty (total shoulder arthroplasty and hemiarthroplasty) and those with a failed primary RTSA to explore revision of which index procedure resulted in better long-term clinical outcomes. Methods: In this prospective, multicenter, observational study, patients underwent revision RTSA using an inverted-bearing prosthesis. We recorded clinical scores, active range of motion, pain, satisfaction, and the rate of scapular notching. Complications and prosthesis survival were also noted. Results: We included 45 patients (45 shoulders) with revision RTSA for failed primary anatomic shoulder arthroplasty (30 patients) and RTSA (15 patients). Clinical and radiographic outcomes were recorded from 36 patients at a median follow-up of 101.6 months, and prosthesis survival was assessed from all 45 patients. At final follow-up, clinical scores (P < .05), abduction (P = .032), re-revision rate (P = .018), and prosthesis survival (P = .015) were significantly better in patients revised from failed primary anatomic shoulder arthroplasty than those from RTSA. However, pain, satisfaction, and overall complication rates were similar in both groups (P > .05). Conclusions: We found better long-term clinical scores, abduction, and prosthesis survival rates after failed primary anatomic shoulder arthroplasty than after RTSA. Pain reduction and complication rates were comparable in both groups. Thus, anatomic shoulder arthroplasty remains an attractive option for primary arthroplasty in selected cases.

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PURPOSE: The aim of this study was to observe the effects of changing humeral tray thickness on the resultant of intraoperative glenohumeral joint loads using a load-sensing system (LSS). METHODS: An rTSA was performed on fresh frozen full-body cadaver shoulders by using an internal proprietary LSS on the humeral side. The glenohumeral loads (Newtons) and the direction of the resultant force applied on the implant were recorded during four standard positions (External rotation, Extension, Abduction, Flexion) and three "complex" positions of Activity Daily Life ("behind back", "overhead reach" and "across chest"). For each position, the thickness was increased from 0 to 6 mm in a continuous fashion using the adjustment feature of the humeral system. Each manoeuvre was repeated three times. RESULTS: All shoulder positions showed a high repeatability of the glenohumeral load magnitude measured with an intra-class correlation coefficient of over 0.9. For each position, we observed a strong but no linear correlation between humeral tray thickness and joint loads. It was a cubical correlation (rs = 0,91) with a short ascending phase, then a plateau phase, and finally a phase with an exponential growth of the loads on the humeral implant. In addition, an increase in trail-poly thickness led to a recentering of force application at the interface of the two glenohumeral implants. CONCLUSION: This study provides further insight into the effects of humeral implant thickness on rTSA glenohumeral joint loads during different positions of the arm. Data obtained using this type of device could guide surgeons in finding the proper implant balance during rTSA.

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BACKGROUND: Stilting is a novel technique used in reverse shoulder arthroplasty (RSA) in patients with significant glenoid bone loss. This technique utilizes peripheral locking screws placed behind an unseated portion of the baseplate, to transmit forces from the baseplate to the cortical surface of the glenoid, without the need for bone grafting. The stilted screw, once locked, provides a fixed angle point of support for an unseated aspect of a baseplate. The primary advantages of this technique are reduced cost compared to a custom implant and reduced operative time compared to bone grafting. METHODS: We conducted a retrospective, non-randomized, comparative cohort study of 41 patients underwent primary Reverse Shoulder Arthroplasty (RSA) using the Stilting Technique with the Exactech Equinoxe Reverse System (Gainesville, FL, USA) at a single, academic center from the years 2004-2021. Exclusion criteria included age under 18 or over 100, and oncologic or acute fracture RSA indications. Operative data was documented, including implant records, percent baseplate seating, and operative duration. Survivorship was compared among primary stilted-RSA (n=41), bone graft-RSA (n=42), and non-stilted/non-bone grafted RSA (n=1,032) within our institutional shoulder arthroplasty database. A radiographic examination of baseplate failure was also conducted across the study groups. Postoperative functional outcomes were compared in a matched analysis involving patients with a minimum 2-year follow-up between stilted patients and a non-stilted/non-bone grafted control group for primary RSA. RESULTS: All Stilted-RSA cases utilized metal augments and demonstrated a mean baseplate seating of 61% (range 45-75%). For stilted RSAs, survivorship was 100% and 92.6% at 2- and 5-years, compared to 98.3% and 94.6% for non-stilted/non-bone grafted and 96.3% and 79.5% for bone-grafted RSAs (p=0.042). At 5-years, the baseplate-related failure rates were greater in the stilted (7.4%) and the bone-grafted (9.3%) cohorts compared with the non-stilted/non-bone grafted cohort (1.1%, p<0.001). The mean time to baseplate failure was 30 months for stilted RSA. Functional outcomes for primary RSA were statistically similar between stilted and non-stilted patients, including range of motion, Constant, ASES, SST, UCLA, and SPADI scores. CONCLUSION: The stilted-RSA cohort exhibited noninferior revision and baseplate failure rates to that of bone-grafted RSA. This suggests that stilting may be a viable technique for patients undergoing primary RSA with significant glenoid deformity.

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Rotator cuff arthropathy is a spectrum of disease states secondary to full-thickness cuff tears classified by rotator cuff insufficiency and degenerative disease within the shoulder joint. Diagnosis can be made through standard physical exam and radiographic films demonstrating varying levels of weakness, along with acetabularization, femoralization, and superior migration of the humeral head. Severity of disease is classified through both the Hamada and Seebauer grading systems, which are used clinically to determine the appropriate treatment algorithm. Treatment exists along the spectrum from conservative therapy with physical therapy to a definitive treatment with total joint replacement. Depending on a patient's progression and other comorbidities, arthroscopic treatments may additionally be used in specific circumstances as joint-sparing techniques. In recent years, reverse total shoulder arthroplasty has produced increasingly favorable outcomes with improvements in pain and function while simultaneously diminishing complication rates, making it generally accepted as standard of care. This disease limits quality of life for a large population of patients and efforts toward optimization of the treatment regimen is critical. This review provides an overview on the diagnostic criteria, classification, pathoanatomic changes, biomechanics, treatment options, outcomes, and complications of rotator cuff arthropathy.

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Glenoid bone loss from an infiltrating intramuscular lipoma causing erosive changes is a rare occurrence. A 71-year-old woman with symptomatic rotator cuff arthropathy in the setting of an intramuscular infiltrating lipoma and secondary glenoid bone loss was treated with single-stage tumor excision and reverse total shoulder arthroplasty (rTSA) using an injectable, hard self-setting calcium phosphate as structural bone graft substitute. The patient demonstrated excellent clinical and radiographic outcomes at 2-year follow-up. Infiltrating lipomas resulting in functional rotator cuff arthropathy and erosive osseous glenoid changes are exceedingly rare, yet significant glenoid bony defects present a challenge in the setting of shoulder arthroplasty. This report describes the use of structural bone graft substitute for the management of a glenoid bone defect from a rare case of an intramuscular infiltrating lipoma, while maintaining excellent improvement in functional outcomes and pain after rTSA.

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Proximal humerus fractures and injuries to the acromioclavicular joint are among the most common traumatic diseases of the upper extremity. Fractures of the proximal humerus occur most frequently in older people and are an indicator fracture of osteoporosis. While a large proportion of only slightly displaced fractures can be treated non-operatively, more complex fractures require surgical treatment. The choice of optimal treatment and the decision between joint-preserving surgery by means of osteosynthesis or endoprosthetic treatment is often a difficult decision in which both fracture morphology factors and individual factors should be taken into account. If endoprosthetic treatment is indicated, satisfactory long-term functional and clinical results have been achieved with a reverse shoulder arthroplasty. Injuries to the acromioclavicular joint occur primarily in young, athletic individuals. The common classification according to Rockwood divides the injury into 6 degrees of severity depending on the dislocation. This classification forms the basis for the decision on non-operative or surgical treatment. The indication for surgical treatment for higher-grade injuries is the subject of controversial debate in the latest literature. In chronic injuries, an autologous tendon transplant is also performed. Whereas in the past, treatment was often carried out using a hook plate, which was associated with complications, the gold standard today is minimally invasive treatment using Endobutton systems. This review provides an overview of the two injury patterns and discusses the various treatment options.

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BACKGROUND: Augmented baseplates can be effective at addressing eccentric glenoid wear in reverse total shoulder arthroplasty (rTSA). However, these implants often come in a limited number of predetermined shapes that require additional reaming to ensure adequate glenoid seating. This typically involves complex instrumentation and can have a negative impact on implant stability. Modular baseplate augmentation based on intra-operative measurements may allow for more precise defect filling while preserving glenoid bone. The purpose of this investigation was to assess the stability of a novel ringed baseplate with modular augmentation in comparison to non-augmented standard and ringed baseplate designs. METHODS: In this biomechanical study, baseplate micromotion was tested for three constructs according to American Society for Testing and Materials (ASTM) guidelines. The constructs included a non-augmented curved baseplate, a non-augmented ringed baseplate and ringed baseplate with an 8 mm locking modular augmentation peg. The non-augmented constructs were mounted flush onto polyurethane (PU) foam blocks, while the augmented baseplate was mounted on a PU block with a simulated defect. Baseplate displacement was measured prior to and after 100,000 cycles of cyclic loading. RESULTS: Prior to cyclic loading, the non-augmented and augmented ringed baseplates both demonstrated significantly less micromotion than the non-augmented curved baseplate design (81.1 µm vs 97.2 µm vs 152.7 µm; p=0.009). After cyclic loading, both ringed constructs continued to have significantly less micromotion compared to the curved design (105.5 µm vs 103.2 µm vs 136.6 µm; p<0.001). The micromotion for both ringed constructs remained below the minimum threshold required for bony ingrowth (150 µm) at all time points. CONCLUSION: In the setting of a simulated glenoid defect, locked modular augmentation of a ringed baseplate does not result in increased baseplate micromotion when compared to full contact, non-augmented baseplates. This design offers a simple method for tailored baseplate augmentation that can match specific variations in glenoid anatomy, limiting the need for excessive reaming and ultimately optimizing the environment for long term implant stability. LEVEL OF EVIDENCE: Basic Science Study; Biomechanics.

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Background: Shoulder arthroplasty (SA) has been shown to improve quality of life, though outcomes may vary between individuals. Multiple factors may affect outcomes, including preoperative mental health conditions (MHCs). The goal of this systematic review was to evaluate the clinical and functional outcomes after SA in patients with MHC compared to patients without MHC. Methods: This systematic review was performed in adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines outlined by Cochrane Collaboration. A search of PubMed, the Medline Library, and EMBASE was conducted from inception until September 2023 to obtain studies reporting outcomes after total shoulder arthroplasty and reverse total shoulder arthroplasty in patients with and without MHC. Study characteristics and information on clinical and functional outcomes were collected. All included studies were case-control studies. The methodological quality of the included primary studies was appraised using the methodological index for nonrandomized studies scoring. Results: Eleven articles published between 2016 and 2023 met inclusion criteria. In total, 49,187 patients, 49,289 shoulders, and five different MHC were included. 8134 patients in the cohort had a diagnosed MHC. The mean patient age was 67.8 years (range, 63.5-71.6 years), and 52.6% of the patients were female. The mean follow-up time was 35.5 months (range, 16.2-58.3 months). Reverse total shoulder arthroplasty was the most common type of procedure (25,543 shoulders, 51.8%). Depression and anxiety were the most reported psychiatric diagnoses (7990 patients, 98.2%). Patients with versus without MHC reported mean improvements of 38 and 42 in American Shoulder and Elbow Surgeons shoulder score and mean Visual Analog Scale pain improvements of 4.7 and 4.9, respectively. Mean complication rates of 31.4% and 14.2% were observed in patients with versus without MHC, respectively. The most prevalent surgical complication in patients with MHC was infection (1.8%), followed by prosthetic complication (1.7%), and adhesive capsulitis (1.6%). Conclusions: Patients with MHC may have lower preoperative range of motion, worse postoperative shoulder function, and higher postoperative pain levels than patients without MHC. Patients with MHC demonstrated improvements in range of motion and functional outcomes after SA but had higher reported complication and revision rates when compared to patients without MHC. Depression and anxiety were the leading conditions correlated with lower outcomes in patients with MHC after SA. Preoperative physical therapy, mental health counseling, and expectation setting may help these patients reach the maximal achievable benefit from SA.

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OpenSim Moco enables solving for an optimal motion using Predictive and Tracking simulations. However, Predictive simulations are computationally prohibitive, and the efficacy of Tracking in deviating from its reference is unclear. This study compares Tracking and Predictive approaches applied to the generation of morphology-specific motion in statistically-derived musculoskeletal shoulder models. The signal analysis software, CORA, determined mean correlation ratings between Tracking and Predictive solutions of 0.91 ± 0.06 and 0.91 ± 0.07 for lateral and forward-reaching tasks. Additionally, Tracking provided computational speed-up of 6-8 times. Therefore, Tracking is an efficient approach that yields results equivalent to Predictive, facilitating future large-scale modelling studies.

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BACKGROUND: Superior capsular reconstruction (SCR) and reverse total shoulder arthroplasty (RTSA) are widely performed in patients with irreparable rotator cuff tears, including pseudoparalytic shoulder (PPS), and have shown positive clinical outcomes. However, limited studies have compared these two in terms of functional recovery in patients with PPS without osteoarthritic change. Thus, this study aimed to compare the clinical outcomes and to clarify the characteristics and differences in temporal changes among patients who underwent either RTSA or SCR using tensor fascia lata for PPS due to irreparable rotator cuff tear without osteoarthritic change (Hamada grade ≤ 3). METHODS: We enrolled a total of 39 patients who underwent SCR (n = 20) or RTSA (n = 19 cases) with a follow-up period of 2 years. All patients were follow-up at 2, 3, 4, 5, 6, 8, 10, 12, and 24 months postoperatively. Preoperative and postoperative range of motion (ROM), American Shoulder and Elbow Surgeons (ASES) scores, and temporal changes in ROMs were compared between the two groups. RESULTS: The SCR group had significantly better ROM than the RTSA group in flexion (146° ± 34° vs. 132° ± 23°, P = 0.022), abduction (147° ± 36° vs. 130° ± 23°, P = 0.0092), internal rotation (11 ± 3 Th10 vs. 6 ± 3 L3, P < 0.001), and ASES score (84.1 ± 13.8 vs. 80.1 ± 6.1, P = 0.0096). While the RTSA group achieved 100° in flexion and abduction after 3 months postoperatively, the SCR group took approximately 5 months. However, the SCR group exceeded the RTSA group in flexion and abduction at six months postoperatively. In the SCR group, some patients with irreparable subscapularis tendon tears could not achieve 90° shoulder elevation. Both groups showed significant improvements in shoulder flexion and abduction compared to the preoperative state (P < 0.001). CONCLUSION: Although SCR requires a longer rehabilitation period, it provides similar outcomes to RTSA after two years for non-osteoarthritic, irreparable cuff tears with pseudoparalysis.

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BACKGROUND: Humeral component retroversion (HcRV) can be customized to match native humeral retroversion (RV) during reverse total shoulder arthroplasty (RTSA). However, assessing postoperative individualized HcRV using computed tomography (CT) scans without an elbow can be challenging. Therefore, we developed a new method to obtain the HcRV and evaluated its reliability. METHODS: A total of 106 patients underwent RTSA using a single implant, in which the humeral component was implanted based on the preoperative humeral RV (Pre_HRV) using a bilateral CT scan of the elbow. Intraoperatively, a retroversion guide with version hole at 10° intervals was used; Pre_HRV was converted to 5° increments and applied for humeral component implantation. The axis of intertubercular sulcus (ITS) was defined as the line perpendicular to the intertubercular line, and the angle between the axis of ITS and the trans-epicondylar axis was defined as the bicipital groove rotation (BGR). ITS orientation was defined as the angle between the axis of ITS and the central axis of the humeral head. Since the BGR does not change, the postoperative implanted HcRV (Post_HcRV)f is calculated as the BGR minus the value of the postoperative ITS orientation. An agreement analysis was performed between Post_HcRV and both the intraoperatively applied humeral RV (I_HRV) and Pre_HRV, as well as between the pre- and postoperative ITS orientations. The humeral component's insertional errors were also evaluated. RESULTS: All radiologic measurements exhibited excellent inter- and intra-observer reliabilities. The reliabilities between Post_HcRV and both I_HRV and Pre_HRV, as well as between pre- and postoperative ITS orientations, showed excellent agreement (intraclass correlation coefficients: 0.953, 0.952, and 0.873, respectively). The humeral component was inserted within 5° in 86.8% of the planned humeral RV cases. CONCLUSIONS: The HcRV measured using the BGR and ITS orientations achieved good accuracy for restoring the planned humeral RV using a retroversion guide with the forearm axis. Therefore, this new radiological measurement method can aid orthopedic surgeons in confirming Post_HcRV on CT scans without an elbow.

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BACKGROUND: While both anatomic (ATSA) and reverse total shoulder arthroplasty (RTSA) have been popularized as a means of treating individuals with degenerative shoulder conditions, the indications for each can vary widely amongst providers. While surgeons with differing fellowship training commonly perform these procedures, it is not understood how fellowship training influences choice of implant. METHODS: A national database was queried to identify surgeons performing anatomic and reverse total shoulder arthroplasty. For all surgeons who performed more than 10 cases between 2010-2022, fellowship data was individually collected via online search. For each fellowship group, rates of anatomic and reverse total shoulder arthroplasty were identified using International Classification of Diseases (ICD) procedural codes. Those undergoing revision arthroplasty and those with a history of fracture, infection, or malignancy were excluded. Primary outcome measures included the proportion of primary and revision ATSA and RTSA by fellowship in addition to the rate of RTSA performed for a primary diagnosis of glenohumeral osteoarthritis. RESULTS: A total of 131,974 patients met the inclusion criteria and were retained for this study. RTSA increased from 50.1% of all primary shoulder arthroplasty cases in 2011 to 72.0% in 2022. After adjusting for age and comorbidities, Sports Medicine fellowship-trained (Sports) surgeons opted for primary RTSA over ATSA at a significantly higher rate than Shoulder and Elbow fellowship-trained (Shoulder) surgeons and surgeons who completed another type of fellowship or no fellowship (Other). Sports surgeons also chose RTSA more frequently for the diagnosis of glenohumeral osteoarthritis compared to Shoulder surgeons. Surgeons in the Other cohort were more likely to perform primary ATSA rather than RTSA in comparison to surgeons in the Shoulder and Sports cohorts. Sports surgeons were responsible for the greatest increase in percentage of all shoulder arthroplasty procedures from 2010-2022 (28.4% to 40.4%) while the Other group decreased by a comparable amount (45.9% to 32.4%) over the same period. CONCLUSION: Surgeons who have completed a Sports Medicine fellowship choose RTSA over ATSA at a higher rate than Shoulder and Elbow surgeons, both for all indications and also for a primary diagnosis of glenohumeral osteoarthritis. Those who have no fellowship training or fellowship training outside of Sports Medicine and Shoulder and Elbow surgery have the highest percentage of ATSA in their arthroplasty practice. Revision anatomic and revision reverse total shoulder arthroplasty represents a larger percentage of overall case volume for Shoulder and Elbow surgeons.

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Reverse total shoulder arthroplasty (RSA) was historically reserved for the elderly, low-demand patient with rotator cuff arthropathy (RCA) or as a salvage procedure after failed primary arthroplasty. Surgeon expertise and the advancement of implant design has allowed RSA to now become commonplace not only for RCA but also for glenohumeral osteoarthritis. RSA provides a robust glenoid baseplate fixation, which allows for easier and more reliable bone grafting or augmentation when needed. For patients with severe glenoid bone loss, RSA has been shown to have superior or equivalent patient-reported outcomes and shoulder range of motion when compared with total shoulder arthroplasty.

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BACKGROUND: Reverse total shoulder arthroplasty (RTSA) is the standard of care for patients with glenohumeral osteoarthritis and rotator cuff deficiency. Preoperative RTSA planning based on medical images and patient-specific instruments has been established over the last decade. This study aims to determine the effects of using augmented reality-assisted intraoperative navigation (ARIN) for baseplate positioning in RTSA compared to preoperative planning. It is hypothesized that ARIN will decrease deviation between preoperative planning and postoperative baseplate positioning. Moreover, ARIN will decrease deviation between the (senior) more (>50 RTSAs/yr) and less experienced (junior) surgeon (5-10 RTSAs/yr). METHODS: Preoperative CT scans of 16 fresh-frozen cadaveric shoulders were obtained. Baseplate placements were planned using a validated software. The data were then converted and uploaded to the augmented reality system (NextAR; Medacta International). Each of the 8 RTSAs were implanted by a senior and a junior surgeon, with 4 RTSAs using ARIN and 4 without. A postoperative CT scan was performed in all cases. The scanned scapulae were segmented, and the preoperative scan was laid over the postoperative scapula by the nearest iterative point cloud analysis. The deviation from the planned entry point and trajectory was calculated regarding the inclination, retroversion, medialization (reaming depth) and lateralization, anteroposterior position, and superoinferior position of the baseplate. Data are reported as mean ± standard deviation (SD) or mean and 95% confidence interval (CI). P values < .05 were considered statistically significant. RESULTS: The use of ARIN yielded a reduction in the absolute difference between planned and obtained inclination from 9° (SD: 4°) to 3° (SD: 2°) (P = .011). Mean difference in planned-obtained inclination between surgeons was 3° in free-hand surgeries (95% CI: -4 to 10; P = .578), whereas this difference reduced to 1° (95% CI: -6 to 7, P = .996) using ARIN. Retroversion, medialization (reaming depth) and lateralization, anteroposterior position, and superoinferior position of the baseplate were not affected by using ARIN. Surgical duration was increased using ARIN for both the senior (10 minutes) and junior (18 minutes) surgeon. CONCLUSIONS: The implementation of ARIN leads to greater accuracy of glenoid component placement, specifically with respect to inclination. Further studies have to verify if this increased accuracy is clinically important. Furthermore, ARIN allows less experienced surgeons to achieve a similar level of accuracy in component placement comparable to more experienced surgeons. However, the potential advantages of ARIN in RTSA are counterbalanced by an increase in operative time.