Impact of Deltoid Computer Tomography Image Data on the Accuracy of Machine Learning Predictions of Clinical Outcomes after Anatomic and Reverse Total Shoulder Arthroplasty.

Background: Despite the importance of the deltoid to shoulder biomechanics, very few studies have quantified the three-dimensional shape, size, or quality of the deltoid muscle, and no studies have correlated these measurements to clinical outcomes after anatomic (aTSA) and/or reverse (rTSA) total shoulder arthroplasty in any statistically/scientifically relevant manner. Methods: Preoperative computer tomography (CT) images from 1057 patients (585 female, 469 male; 799 primary rTSA and 258 primary aTSA) of a single platform shoulder arthroplasty prosthesis (Equinoxe; Exactech, Inc., Gainesville, FL) were analyzed in this study. A machine learning (ML) framework was used to segment the deltoid muscle for 1057 patients and quantify 15 different muscle characteristics, including volumetric (size, shape, etc.) and intensity-based Hounsfield (HU) measurements. These deltoid measurements were correlated to postoperative clinical outcomes and utilized as inputs to train/test ML algorithms used to predict postoperative outcomes at multiple postoperative timepoints (1 year, 2-3 years, and 3-5 years) for aTSA and rTSA. Results: Numerous deltoid muscle measurements were demonstrated to significantly vary with age, gender, prosthesis type, and CT image kernel; notably, normalized deltoid volume and deltoid fatty infiltration were demonstrated to be relevant to preoperative and postoperative clinical outcomes after aTSA and rTSA. Incorporating deltoid image data into the ML models improved clinical outcome prediction accuracy relative to ML algorithms without image data, particularly for the prediction of abduction and forward elevation after aTSA and rTSA. Analyzing ML feature importance facilitated rank-ordering of the deltoid image measurements relevant to aTSA and rTSA clinical outcomes. Specifically, we identified that deltoid shape flatness, normalized deltoid volume, deltoid voxel skewness, and deltoid shape sphericity were the most predictive image-based features used to predict clinical outcomes after aTSA and rTSA. Many of these deltoid measurements were found to be more predictive of aTSA and rTSA postoperative outcomes than patient demographic data, comorbidity data, and diagnosis data. Conclusions: While future work is required to further refine the ML models, which include additional shoulder muscles, like the rotator cuff, our results show promise that the developed ML framework can be used to evolve traditional CT-based preoperative planning software into an evidence-based ML clinical decision support tool.

Stratification of the Minimal Clinically Important Difference, Substantial Clinical Benefit, and Patient Acceptable Symptomatic State after Total Shoulder Arthroplasty by Implant Type, Preoperative Diagnosis, and Sex.

BACKGROUND: Clinical significance, as opposed to statistical significance, has increasingly been utilized to evaluate outcomes after total shoulder arthroplasty (TSA). The purpose of this study was to identify thresholds of the minimal clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptomatic state (PASS) for TSA outcome metrics and determine if these thresholds are influenced by prosthesis type (anatomic or reverse TSA), sex, or preoperative diagnosis. METHODS: A prospectively collected international multicenter database inclusive of 38 surgeons was queried for patients receiving a primary aTSA or rTSA between 2003 and 2021. Prospectively, outcome metrics including ASES, shoulder function score (SFS), SST, UCLA, Constant, VAS Pain, shoulder arthroplasty smart (SAS) score, forward flexion, abduction, external rotation, and internal rotation was recorded preoperatively and at each follow-up. A patient satisfaction question was administered at each follow-up. Anchor-based MCID, SCB, and PASS were calculated as defined previously overall and according to implant type, preoperative diagnosis, and sex. The percentage of patients achieving thresholds was also quantified. RESULTS: A total of 5,851 total shoulder arthroplasties including aTSA (n=2,236) and rTSA (n=3,615) were included in the study cohort. The following were identified as MCID thresholds for the overall (aTSA + rTSA irrespective of diagnosis or sex) cohort: VAS Pain (-1.5), SFS (1.2), SST (2.1), Constant (7.2), ASES (13.9), UCLA (8.2), SPADI (-21.5), and SAS (7.3), Abduction (13°), Forward elevation (16°), External rotation (4°), Internal rotation score (0.2). SCB thresholds for the overall cohort were: VAS Pain (-3.3), SFS (2.9), SST 3.8), Constant (18.9), ASES (33.1), UCLA (12.3), SPADI (-44.7), and SAS (18.2), Abduction (30°), Forward elevation (31°), External rotation (12°), Internal rotation score (0.9). PASS thresholds for the overall cohort were: VAS Pain (0.8), SFS (7.3), SST (9.2), Constant (64.2), ASES (79.5), UCLA (29.5), SPADI (24.7), and SAS (72.5), Abduction (104°), Forward elevation (130°), External rotation (30°), Internal rotation score (3.2). MCID, SCB, and PASS thresholds varied depending on preoperative diagnosis and sex. CONCLUSION: MCID, SCB, and PASS thresholds vary depending on implant type, preoperative diagnosis, and sex. A comprehensive understanding of these differences as well as identification of clinically-relevant thresholds for legacy and novel metrics is essential to assist surgeons in evaluating their patient's outcomes, interpreting the literature, and counseling their patients preoperatively regarding expectations for improvement. Given that PASS thresholds are fragile and vary greatly depending on cohort variability, caution should be exercised in conflating them across different studies.

Utility of Superior Augments in Reverse Shoulder Arthroplasty (Exactech, Equinoxe GPS) without Significant Glenoid Deformity.

INTRODUCTION: Superior augment use may help avoid superior tilt while minimizing removal of inferior glenoid bone. Therefore, our goal is to compare superior augments versus no augment baseplates in RSA for patients with rotator cuff dysfunction and no significant superior glenoid erosion. METHODS: A multicenter retrospective analysis of 145 patients who underwent RSA with intraoperative navigation (Exactech, Equinoxe GPS) and three-year follow-up (mean 32-month follow-up, range 20 to 61 months) who had preoperative superior inclination less than 10 degrees and retroversion less than 15 degrees. Patient demographics, radiographic measurements, surgical characteristics, patient-reported outcomes at preoperative and postoperative visit closest to three years, and adverse events at final follow-up were obtained. Operative time, planned inclination, and planned version of the baseplate were obtained. Chi-square test used to compare categorical variables and student t-test used to compare augment and no augment cohorts. RESULTS: The study population consisted of 54 superior augment patients and 91 no augment patients. The augment cohort had lower BMI (27.2 vs. 29.4, p-0.023), higher native superior inclination (5.9 vs. 1.4 degrees, p<0.001). No difference between the augment and no augment cohorts was found regarding age (p=0.643), gender (p=0.314), medical comorbidities (p>0.05), surgical indication (p=0.082), and native glenoid version (p=0.564). The augment cohort had higher internal rotation score (4.6 vs. 3.9, p=0.023), all remaining ROM and PROs preoperatively were not significantly different. At final follow-up, active ROM in all planes was not different between the cohorts. Regarding PROs, the postoperative SAS score was significantly higher (78.0 vs. 73.6, p=0.042), and ASES score trended towards higher (83.6 vs. 77.5, p=0.063) in the augment cohort. The augment cohort had significantly lower proportion of patients planned to have superior baseplate tilt (1.9% vs. 14.3%, p=0.012), and had greater mean inclination correction (6.3 vs. 1.3 degrees, p<0.001), compared to no augment cohort. Adverse events were rare, and there was no significant difference found between the augment and no augment cohorts (5.6% vs. 3.3%, p=0.509). DISCUSSION: Superior augmented baseplate in RSA with minimal superior glenoid erosion is associated with similar ROM and adverse events with somewhat improved postoperative PROs compared to non-augmented baseplates at 3-year follow-up. Additionally, superior augments resulted in a greater proportion of baseplates planned to avoid superior tilt, and trended toward shorter operative times. Further investigation of long-term glenoid baseplate loosening is imperative to fully understand the cost-effectiveness of superior augments in the setting of minimal glenoid deformity.

Two-year minimum survivorship and radiographic analysis of a pressfit short humeral stem for total shoulder arthroplasty.

Background: Newer generation humeral stem designs in total shoulder arthroplasty (TSA) are trending towards shorter lengths and uncemented fixation. The goal of this study is to report a 2-yr minimum clinical and radiographic outcomes of an uncemented short-stem press-fit humeral stem in anatomic total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA). Methods: A retrospective multicenter database review was performed of all patients who received an uncemented short-length press-fit humeral stem (Equinoxe Preserve humeral stem, Exactech, Inc., Gainesville, FL, USA) in ATSA and RTSA with a minimum two-year follow-up. The primary outcome was the prevalence of humeral stems at risk of radiographic loosening. Secondary outcomes included evaluation of functional outcome scores and prevalence of revision TSA for humeral stem loosening. Two blinded observers performed radiographic analyses, which included humeral stem alignment, canal filling ratio, radiolucent lines, stress shielding (calcar and greater tuberosity), and changes in component position (subsidence and stem shift). At risk stems were defined by the presence of one or more of the following: humeral stem with shifting or subsidence, scalloping of the humeral cortex, or radiolucent lines measuring 2 mm or greater in 3 or more zones. Results: 287 patients (97 ATSA and 190 RTSA) were included in this study. The mean follow-up was 35.9 (±6.1) months. There were significant improvements for all functional outcome scores (P < .05), range of motion (P < .05), and visual analogue pain scale pain (P < .05). The prevalence of humeral stem at risk of radiographic loosening was 1% in the ATSA group (1/97) and 18.4% in the RTSA group (35/190). Calcar resorption was seen in 34% of ATSA and 19% of RTSA, with severe resorption in 12.4% of ATSA and only 3.2% of RTSA. Greater tuberosity resorption was present in 3.1% of ATSA and 7.9% of RTSA. The mean canal filling ratio was 50.2% (standard deviation 11.2%). Using logistic regression, a significant positive correlation between canal filling ratio and stress shielding (P < .01) was seen for both calcar and tuberosity stress shielding. The revision surgery rate was 0% in ATSA compared to 1.6% in RTSA. Conclusion: This retrospective study demonstrates a low revision rate and low prevalence of humeral stems at risk of radiographic loosening at two years with a press-fit short-stem humeral design in ATSA. Physiologic subsidence of humeral stems can account for higher prevalence of humeral stems at radiographic risk of loosening in RTSA compared to ATSA.

Initial clinical experience with a predictive clinical decision support tool for anatomic and reverse total shoulder arthroplasty.

PURPOSE: Clinical decision support tools (CDSTs) are software that generate patient-specific assessments that can be used to better inform healthcare provider decision making. Machine learning (ML)-based CDSTs have recently been developed for anatomic (aTSA) and reverse (rTSA) total shoulder arthroplasty to facilitate more data-driven, evidence-based decision making. Using this shoulder CDST as an example, this external validation study provides an overview of how ML-based algorithms are developed and discusses the limitations of these tools. METHODS: An external validation for a novel CDST was conducted on 243 patients (120F/123M) who received a personalized prediction prior to surgery and had short-term clinical follow-up from 3 months to 2 years after primary aTSA (n = 43) or rTSA (n = 200). The outcome score and active range of motion predictions were compared to each patient's actual result at each timepoint, with the accuracy quantified by the mean absolute error (MAE). RESULTS: The results of this external validation demonstrate the CDST accuracy to be similar (within 10%) or better than the MAEs from the published internal validation. A few predictive models were observed to have substantially lower MAEs than the internal validation, specifically, Constant (31.6% better), active abduction (22.5% better), global shoulder function (20.0% better), active external rotation (19.0% better), and active forward elevation (16.2% better), which is encouraging; however, the sample size was small. CONCLUSION: A greater understanding of the limitations of ML-based CDSTs will facilitate more responsible use and build trust and confidence, potentially leading to greater adoption. As CDSTs evolve, we anticipate greater shared decision making between the patient and surgeon with the aim of achieving even better outcomes and greater levels of patient satisfaction.

Evaluating the fairness and accuracy of machine learning-based predictions of clinical outcomes after anatomic and reverse total shoulder arthroplasty.

BACKGROUND: Machine learning (ML)-based clinical decision support tools (CDSTs) make personalized predictions for different treatments; by comparing predictions of multiple treatments, these tools can be used to optimize decision making for a particular patient. However, CDST prediction accuracy varies for different patients and also for different treatment options. If these differences are sufficiently large and consistent for a particular subcohort of patients, then that bias may result in those patients not receiving a particular treatment. Such level of bias would deem the CDST "unfair." The purpose of this study is to evaluate the "fairness" of ML CDST-based clinical outcomes predictions after anatomic (aTSA) and reverse total shoulder arthroplasty (rTSA) for patients of different demographic attributes. METHODS: Clinical data from 8280 shoulder arthroplasty patients with 19,249 postoperative visits was used to evaluate the prediction fairness and accuracy associated with the following patient demographic attributes: ethnicity, sex, and age at the time of surgery. Performance of clinical outcome and range of motion regression predictions were quantified by the mean absolute error (MAE) and performance of minimal clinically important difference (MCID) and substantial clinical benefit classification predictions were quantified by accuracy, sensitivity, and the F1 score. Fairness of classification predictions leveraged the "four-fifths" legal guideline from the US Equal Employment Opportunity Commission and fairness of regression predictions leveraged established MCID thresholds associated with each outcome measure. RESULTS: For both aTSA and rTSA clinical outcome predictions, only minor differences in MAE were observed between patients of different ethnicity, sex, and age. Evaluation of prediction fairness demonstrated that 0 of 486 MCID (0%) and only 3 of 486 substantial clinical benefit (0.6%) classification predictions were outside the 20% fairness boundary and only 14 of 972 (1.4%) regression predictions were outside of the MCID fairness boundary. Hispanic and Black patients were more likely to have ML predictions out of fairness tolerance for aTSA and rTSA. Additionally, patients <60 years old were more likely to have ML predictions out of fairness tolerance for rTSA. No disparate predictions were identified for sex and no disparate regression predictions were observed for forward elevation, internal rotation score, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score, or global shoulder function. CONCLUSION: The ML algorithms analyzed in this study accurately predict clinical outcomes after aTSA and rTSA for patients of different ethnicity, sex, and age, where only 1.4% of regression predictions and only 0.3% of classification predictions were out of fairness tolerance using the proposed fairness evaluation method and acceptance criteria. Future work is required to externally validate these ML algorithms to ensure they are equally accurate for all legally protected patient groups.

Prognostic value of the Walch classification for patients before and after shoulder arthroplasty performed for osteoarthritis with an intact rotator cuff.

BACKGROUND: The Walch classification is commonly used by surgeons when determining the treatment of osteoarthritis (OA). However, its utility in prognosticating patient clinical state before and after TSA remains unproven. We assessed the prognostic value of the modified Walch glenoid classification on preoperative clinical state and postoperative clinical and radiographic outcomes in total shoulder arthroplasty (TSA). METHODS: A prospectively collected, multicenter database for a single-platform TSA system was queried for patients with rotator cuff-intact OA and minimum 2 year follow-up after anatomic (aTSA) and reverse TSA (rTSA). Differences in patient-reported outcome scores (Simple Shoulder Test, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, Shoulder Pain and Disability Index, visual analog scale for pain, Shoulder Function score), combined patient-reported and clinical-input scores (Constant, University of California-Los Angeles shoulder score, Shoulder Arthroplasty Smart Score), active range of motion values (forward elevation [FE], abduction, external rotation [ER], internal rotation [IR], and radiographic outcomes (humeral and glenoid radiolucency line rates, scapula notching rate) were stratified and compared by glenoid deformity type per the Walch classification for aTSA and rTSA cohorts. Comparisons were performed to assess the ability of the Walch classification to predict the preoperative, postoperative, and improved state after TSA. RESULTS: 1008 TSAs were analyzed including 576 aTSA and 432 rTSA. Comparison of outcomes between Walch glenoid types resulted in 15 pairwise comparisons of 12 clinical outcome metrics, yielding 180 total Walch glenoid pairwise comparisons for each clinical state (preoperative, postoperative, improvement). Of the 180 possible pairwise Walch glenoid type and metric comparisons studied for aTSA and rTSA cohorts, <6% and <2% significantly differed in aTSA and rTSA cohorts, respectively. Significant differences based on Walch type were seen after adjustment for multiple pairwise comparisons in the aTSA cohort for FE and ER preoperatively, the Constant score postoperatively, and for abduction, FE, ER, Constant score, and SAS score for pre- to postoperative improvement. In the rTSA cohort, significant differences were only seen in abduction and Constant score both postoperatively and for pre- to postoperative improvement. There were no statistically significant differences in humeral lucency rate, glenoid lucency rate (aTSA), scapular notching rate (rTSA), complication rates, or revision rates between Walch glenoid types after TSA. CONCLUSION: Although useful for describing degenerative changes to the glenohumeral joint, we demonstrate a weak association between preoperative glenoid morphology according to the Walch classification and clinical state when evaluating patients undergoing TSA for rotator cuff-intact OA. Alternative glenoid classification systems or predictive models should be considered to provide more precise prognoses for patients undergoing TSA for rotator cuff-intact OA.

Comparison of Survivorship and Failure Modes Between Anatomic and Reverse Total Shoulder Arthroplasty Across Multiple Government Joint Registries for a Single Platform Shoulder System.

INTRODUCTION: We analyzed two different government joint registries for survivorship associated with one platform shoulder system and compared reasons for revision and trends in usage of anatomic total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) over a period of more than 10 years to elucidate reasons for any changes in market trends. METHODS: A review of the United Kingdom (UK) and Aus- tralian national joint registries was performed for a single platform shoulder prosthesis (Equinoxe; Exactech, Inc, Gainesville, Florida, USA) from 2011 to 2022 to investigate changes in annual usage rates of primary aTSA and primary rTSA relative to differences in survivorship and reasons for revision for each prosthesis type. RESULTS: Between June 2011 and July 2022, 633 primary aTSA and 4,048 primary rTSA were performed in Australia, and 1,371 primary aTSA and 3,659 primary rTSA were per- formed in the UK with the same platform shoulder prosthesis. Over this period of use, rTSA utilization increased annually at a greater rate than aTSA for this platform shoulder pros- thesis. Specifically in Australia, primary aTSA use increased annually by an average of 38.3% while primary rTSA use increased annually by an average of 148.9%. Similarly, in the UK, primary aTSA use increased annually by an aver- age of 14.0%, while primary rTSA use increased annually by an average of 32.4%. Additionally, the overall incidence of aTSA and rTSA revisions was low; 99 of 2,004 primary aTSA (4.9%) patients and 216 of 7,707 primary rTSA (2.8%) patients with this specific platform shoulder prosthesis were revised. The average 8-year cumulative revision rate for primary aTSA patients was higher than that for primary rTSA patients; 7.7% of aTSA patients were revised at 8 years (0.96% revised/year), but only 4.4% of primary rTSA patients were revised at 8 years (0.55% revised/year). No difference in hazard ratio for all-cause revisions was ob- served for the Equinoxe aTSA or rTSA as compared to all other aTSA systems in either registry. Some differences in the reasons for revision were observed between aTSA and rTSA, where most importantly, rTSA patients experienced only one case of revision due to rotator cuff tears or sub- scapularis failure as compared to the 34 cases of rotator cuff tears or subscapularis failure with aTSA, which accounted for more than one-third of all aTSA revisions. Furthermore, soft-tissue related failure modes were the most common reasons for aTSA failure and were responsible for 56.5% (34.3% rotator cuff tears or subscapularis failure and 22.2% instability or dislocation) of all aTSA revisions; in contrast, soft-tissue related failure modes were responsible for only 26.9% (26.4% instability or dislocation and 0.5% rotator cuff failure) of all rTSA revisions. CONCLUSIONS: This multi-country registry analysis utiliz- ing independent and unbiased data of 2,004 aTSA and 7,707 rTSA of the same platform shoulder prosthesis demonstrated high aTSA and rTSA survivorship in two different markets over a period of more than 10 years of clinical use. A dra- matic increase in rTSA utilization was observed in each country. Reverse total shoulder arthroplasty patients were demonstrated to have a lower revision rate at 8 years and were not as susceptible to the most common failure mode associated with aTSA: rotator cuff tears or subscapularis failure. The reduction in soft-tissue related failure modes with rTSA may explain why so many more patients are now being treated with rTSA in each market.

Two-year outcomes of the reverse humeral reconstruction prosthesis.

BACKGROUND: Extensive proximal humeral bone loss in the setting of shoulder arthroplasty represents a difficult challenge for the treating surgeon. Achieving adequate fixation with standard humeral prostheses can be problematic. Allograft-prosthetic composites are a viable solution for this problem; however, high rates of complications have been reported. Modular proximal humeral replacement systems are another potential solution, but there is a paucity of outcome data on these implants. This study reports the 2-year minimum follow-up outcomes and complications of a single system reverse proximal humeral reconstruction prosthesis (RHRP) for patients with extensive proximal humeral bone loss. METHODS: We retrospectively reviewed all patients with minimum 2-year follow-up who underwent implantation of an RHRP for either (1) failed shoulder arthroplasty or (2) proximal humerus fracture with severe bone loss (Pharos 2 and 3) and/or sequelae thereof. Forty-four patients met inclusion criteria (average age 68.3 ± 13.1 years). The average follow-up was 36.2 ± 12.4 months. Demographic information, operative data, and complications were recorded. Pre- and postoperative range of motion (ROM), pain, and outcome scores were assessed and compared to the minimal clinically important difference (MCID) and substantial clinical benefit (SCB) for primary rTSA where available. RESULTS: Of the 44 RHRPs evaluated, 93% (n = 39) had undergone prior surgery and 70% (n = 30) were performed for failed arthroplasty. ROM improved significantly in abduction by 22° (P = .006) and forward elevation by 28° (P = .003). Average pain on a daily basis and pain at worst improved significantly, by 2.0 points (P < .001) and 2.7 points (P < .001), respectively. Mean Simple Shoulder Test score improved by 3.2 (P < .001), Constant score by 10.9 (P = .030), American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) score by 29.7 (P < .001), University of California, Los Angeles (UCLA), score by 10.6 (P < .001), and Shoulder Pain and Disability Index score by 37.4 (P < .001). A majority of patients achieved the MCID for all outcome measures assessed (56%-81%). The SCB was exceeded by half of patients for forward elevation and the Constant score (50%), and exceeded by the majority of patients for the ASES score (58%) and UCLA score (58%). The complication rate was 28%; the most common complication was dislocation requiring closed reduction. Notably, there were no occurrences of humeral loosening requiring revision surgery. DISCUSSION: These data demonstrate that the RHRP resulted in significant improvements in ROM, pain, and patient-reported outcome measures, without the risk of early humeral component loosening. RHRP represents another potential solution for shoulder arthroplasty surgeons when addressing extensive proximal humerus bone loss.

Impact of accumulating risk factors on the acromial and scapular fracture rate after reverse total shoulder arthroplasty with a medialized glenoid-lateralized humerus onlay prosthesis.

BACKGROUND: Identifying risk factors for acromial and scapular fractures improves our understanding about which variables are relevant to these fracture complications; however, these data are difficult to integrate into clinical practice because the majority of reverse total shoulder arthroplasty (rTSA) patients have ≥1 risk factor. The goal of this study was to better facilitate preoperative identification of patients at risk of acromial and scapular fractures and quantify the impact of accumulating risk factors on the incidence of fracture. METHODS: We retrospectively analyzed 9079 rTSA patients from a multicenter database of rTSA procedures performed with a single medialized glenoid-lateralized humerus onlay rTSA prosthesis to quantify the rate of acromial and scapular fractures. Univariate and multivariate analyses were performed to identify risk factors for fracture. Next, we quantified the number of patients with 1 or multiple significant risk factors for fracture. Finally, to facilitate preoperative identification of patients most at risk of fracture, we stratified our data set using multiple combinations of age, sex, and diagnosis risk factors and calculated the odds ratio for each cohort to quantify the impact of accumulating risk factors on the incidence of fracture. RESULTS: A fracture of the acromion or scapula was radiographically identified in 138 of 9079 patients, for a rate of 1.52%. Patients with fractures were more likely to be older, of female sex, to have a diagnosis of rheumatoid arthritis and/or cuff tear arthropathy, and were less likely to have a diagnosis of diabetes. Eighty-five percent of rTSA patients had ≥1 fracture risk factor. Individually, age, sex, or diagnosis failed to identify any patient cohort with an odds ratio >2.5. Use of multiple combinations of patient risk factors refined the identification of at-risk patients better than any individual risk factor or 2-risk factor combination and demonstrated that the patients with the greatest fracture risk were female patients with a rheumatoid arthritis diagnosis who were aged >70, >75, and >80 years. CONCLUSION: This 9079-rTSA multicenter study demonstrated that 1.52% of patients experienced acromial and/or scapular fractures with a single medialized glenoid-lateralized humerus onlay rTSA prosthesis. Our analysis identified numerous risk factors and quantified the impact of accumulating risk factors on fracture incidence. Patients who are considering rTSA and who have these age, sex, and diagnosis risk factors should be made aware of their elevated complication risk.

Aseptic glenoid baseplate loosening after reverse total shoulder arthroplasty with a single prosthesis.

BACKGROUND: Early reverse total shoulder arthroplasty (rTSA) designs had high failure rates, mainly from loosening of the glenoid baseplate. The purpose of this study was to determine the incidence of aseptic glenoid baseplate loosening after primary rTSA using a contemporary medialized glenoid-lateralized humerus system and identify significant risk factors associated with loosening. METHODS: A total of 7162 patients underwent primary rTSA with a single-platform rTSA system between April 2007 and August 2021; of these primary rTSA patients, 3127 with a minimum 2-year follow-up period were identified. Patients with aseptic glenoid baseplate loosening were compared with all other primary rTSA patients without loosening. Univariate and multivariate analyses were performed to compare these cohorts and identify the demographic characteristics, comorbidities, operative parameters, and implant characteristics associated aseptic glenoid loosening after rTSA. Odds ratios (ORs) were calculated for each significant risk factor and for multiple combinations of risk factors. RESULTS: Irrespective of minimum follow-up, 53 of 7162 primary rTSA shoulders (31 female and 22 male shoulders) experienced aseptic glenoid loosening, for an overall rate of 0.74%. At latest (2-year minimum) follow-up, 30 of 3127 patients experienced aseptic glenoid loosening and showed significantly lower clinical scores, function, and active range of motion and higher pain scores than patients without loosening. Univariate analysis identified rheumatoid arthritis (P = .029; OR, 2.74) and diabetes (P = .028; OR, 1.84) as significant risk factors for aseptic glenoid loosening after rTSA, and multivariate analysis identified Walch glenoid types B2 (P = .002; OR, 4.513) and B3 (P = .002; OR, 14.804), use of expanded lateralized glenospheres (P = .025; OR, 2.57), and use of augmented baseplates (P = .001; OR, 2.50) as significant risk factors. CONCLUSION: The incidence of aseptic glenoid baseplate loosening was 0.74% for the evaluated medialized glenoid-lateralized humerus rTSA system. Numerous risk factors for aseptic loosening were identified, including rheumatoid arthritis, diabetes, Walch type B2 and B3 glenoids, posteriorly-superiorly augmented baseplates, and expanded lateralized glenospheres. Finally, analysis of multiple combinations of risk factors identified patients and implant configurations with the greatest risk of aseptic glenoid loosening.

Longitudinal analysis of shoulder arthroplasty utilization, clinical outcomes, and value: a comparative assessment of changes in improvement over 15 years with a single platform shoulder prosthesis.

BACKGROUND: The goal of this longitudinal analysis of anatomic total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) utilization from 2007 to 2021 is to quantify changes in clinical outcomes, cost, and value, resulting from the introduction and adoption of new shoulder arthroplasty (SA) technologies. METHODS: We analyzed an international database of a single SA prosthesis (Equinoxe; Exactech, Inc.; Gainesville, FL, USA) for all clinical sites that have continuously enrolled cases from 2007 to 2021 to compare changes in primary aTSA and primary rTSA utilization and outcomes across 3, 5-year cohorts based upon the date of implantation. A value analysis was conducted across the 5-year implantation cohorts, with value measured by the ratio of each postoperative outcome measure at 24-36 months and 36-60 months after surgery, and the average implant selling price each year for the U.S. sites in constant 2007 U.S. dollars. These measures of value were compared between cohorts to quantify the impact of new technology introduced over the study period. RESULTS: A dramatic increase in rTSA utilization was observed across the 6 sites over the 15-year study period, along with a rapid adoption of new aTSA and rTSA technologies. The average patient receiving primary aTSA and primary rTSA changed over the 15-year study period, with significant shifts in diagnosis, comorbidities, and preoperative functional status. A comparison of postoperative results demonstrated that both aTSA and rTSA clinical and radiographic outcomes showed improvement relative to 2007-2011. Over this 15-year study period, the average aTSA implant selling price has been relatively stable while the average rTSA implant selling price has significantly declined. As a result, the value associated with the Equinoxe rTSA significantly increased for nearly every outcome measure at 24-36 months and 36-60 months after surgery, while value associated with the Equinoxe aTSA stayed relatively constant from 2007 to 2021. CONCLUSION: Our 6042-patient longitudinal analysis quantified numerous changes in utilization, outcomes, and value across 6 clinical sites over the 15-year study period. Rapid adoption of new aTSA and rTSA technologies was observed and clinical and radiographic outcomes improved relative to 2007-2011. These clinical improvements, in combination with steady aTSA and declining rTSA implant prices, have driven rTSA value to continuously increase while aTSA value has been maintained at a high-level over the 15-year study period with this particular SA system, even when considering the cost and adoption of new technologies.

Augmented baseplates yield optimum outcomes when compared with bone graft augmentation for managing glenoid deformity during reverse total shoulder arthroplasty: a retrospective comparative study.

PURPOSE: The purpose of this study was to compare the outcomes of primary reverse total shoulder arthroplasty (rTSA) using glenoid bone grafting (BG rTSA) with primary rTSA using augmented glenoid baseplates (Aug rTSA) with a minimum 2-year follow-up. METHODS: A total of 520 primary rTSA patients treated with 8° posterior glenoid augments (n = 246), 10° superior glenoid augments (n = 97), or combined 10° superior/8° posterior glenoid augments (n = 177) were compared with 47 patients undergoing glenoid bone grafting for glenoid bone insufficiency. The mean follow-up was 37.0(±16) and 53.0(±27) months, respectively. Outcomes were analyzed preoperatively and at the latest follow-up using conventional statistics and stratification by minimum clinically important difference (MCID) and substantial clinical benefit (SCB) thresholds where applicable. Radiographs were analyzed for baseplate failure, and the incidences of postoperative complications and revisions were recorded. RESULTS: The glenoid Aug rTSA cohort had greater improvements in patient-reported outcome measures (PROMs) and range of motion when compared with the BG rTSA group at a minimum of 2-year follow-up, including Simple Shoulder Test, Constant score, American Shoulder and Elbow Surgeons score, University of California Los Angeles score, Shoulder Pain and Disability Index score, shoulder function, Shoulder Arthroplasty Smart score, abduction, and external rotation (P < .05). Patient satisfaction was higher in the Aug rTSA group compared with the BG rTSA group (P = .006). The utilization of an augmented glenoid component instead of glenoid bone grafting resulted in approximately 50% less total intraoperative time (P < .001), nearly 33% less intraoperative blood loss volume (P < .001), approximately 3-fold less scapular notching (P < .01), and approximately 8-fold less adverse events requiring revision (P < .01) when compared with the BG rTSA cohort. Aside from SCB for abduction, the Aug rTSA cohort achieved higher rates of exceeding MCID and SCB for every PROM compared with BG rTSA. More specifically, 77.6% and 70.2% of the Aug rTSA achieved SCB for American Shoulder and Elbow Surgeons and Shoulder Pain and Disability Index vs. 55% and 48.6% in the BG rTSA, respectively (P = .003 and P = .013). CONCLUSION: The present midterm clinical and radiographic study demonstrates that the utilization of an augmented baseplate for insufficient glenoid bone stock is superior as judged by multiple PROMs and range of motion metrics when compared with bone graft augmentation at minimum 2-year follow-up. In addition, when analyzed according to MCID and SCB thresholds, the use of augmented baseplates outperforms the use of glenoid bone grafting. Complication and revision rates also favor the use of augmented glenoid baseplates over glenoid bone grafting. Long-term clinical and radiographic follow-up is necessary to confirm that these promising midterm results are durable.

Early clinical outcomes following navigation-assisted baseplate fixation in reverse total shoulder arthroplasty: a matched cohort study.

BACKGROUND: Accurate placement of the glenoid baseplate is an important technical goal of reverse total shoulder arthroplasty (RSA). The use of computer navigated instrumentation has been shown to improve the accuracy and precision of intraoperative execution of preoperative planning. The purpose of this study was to compare early clinical outcomes of patients undergoing navigated RSA vs. a non-navigated matched cohort. METHODS: A retrospective review of a prospectively collected shoulder arthroplasty database was used to identify 113 patients from a single institution who underwent navigated primary RSA with a minimum 2-year follow-up. A matched cohort of 113 non-navigated RSAs was created based on sex, age, follow-up, and preoperative diagnosis. Preoperative and postoperative range of motion, functional outcome scores, and complications were reported. RESULTS: A total of 226 shoulders with a mean age of 71 years were evaluated after navigated (113) or non-navigated (113) RSAs. The mean follow-up was 32.8 months (range: 21-54 months). At the final postoperative follow-up, the navigated group had better active forward elevation (135° vs. 129°, P = .023), active external rotation (39° vs. 32°, P = .003), and Constant scores (71.1 vs. 65.5, P = .003). However, when comparing improvements from the preoperative state, there was no statistically significant difference in range of motion or functional outcome scores between the groups. Complications occurred in 1.8% (2) of patients undergoing navigated RSA compared with 5.3% (6) in the non-navigated group (P = .28). Scapular notching (3.1% vs. 8.0%, P = .21) and revision surgery (0.9% vs. 3.5%, P = .37) were more common in non-navigated shoulders. CONCLUSION: At early follow-up, navigated and non-navigated RSAs yielded similar rates of improvement in range of motion and functional outcome scores. Notching and reoperation was more common in non-navigated shoulders, but did not reach statistical significance. Longer follow-up and larger cohort size are needed to determine if intraoperative navigation lengthens the durability of RSA results and reduces the incidence of postoperative complications.

Reverse shoulder arthroplasty with and without baseplate wedge augmentation in the setting of glenoid deformity and rotator cuff deficiency-a multicenter investigation.

INTRODUCTION: Glenoid baseplate augments have recently been introduced as a way of managing glenoid monoplanar or biplanar abnormalities in reverse shoulder arthroplasty (RSA). The purpose of this study is to evaluate the difference in clinical outcomes, complications, and revision rates between augmented and standard baseplates in RSA for rotator cuff arthropathy patients with glenoid deformity. METHODS: A multicenter retrospective analysis of 171 patients with glenoid bone loss who underwent RSA with and without augmented baseplates was performed. Preoperative inclusion criteria included minimum follow-up of 2 years and preoperative retroversion of 15°-30° and/or a beta angle 70°-80°. Version and beta angle were measured on computed tomographic scans, when available, and plain radiographs. Shoulder range of motion (ROM) and patient-reported outcomes were obtained from preoperative and multiple postoperative time points. RESULTS: The study consisted of 84 standard baseplate patients and 87 augmented baseplate patients. The augment cohort had greater mean preoperative glenoid retroversion (17° vs. 9°, P < .001). At >5-year follow-up, the increase in postoperative active abduction (52° vs. 31°, P = .023), forward flexion (58° vs. 35°, P = .020), and internal rotation score (2.8° vs. 1.1°, P = .001) was significantly greater in the augment cohort. Additionally, >5-year follow-up American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score (87.0 ± 16.6 vs. 75.9 ± 22.4, P = .022), Constant score (78.0 ± 9.7 vs. 64.6 ± 15.1, P < .001), and Shoulder Arthroplasty Smart score (81.2 ± 6.5 vs. 71.2 ± 13.6, P = .003) were significantly higher in the augment cohort. Revision rate was low overall, with no difference between the augment and no augment groups (0.7% vs. 3.0%, P = .151). CONCLUSION: In comparing augments to standard nonaugment baseplates in the setting of RSA with glenoid deformity, our results demonstrate greater postoperative improvements in multiple planes of active ROM in the augment cohort. Additionally, the augment cohort demonstrated greater postoperative level and improvement in scores for multiple clinical outcome metrics up to >5 years of follow-up with no difference in complication or revision rates, supporting the use of augmented glenoid baseplates in RSA with glenoid deformity.

Characteristics of anatomic and reverse total shoulder arthroplasty patients who achieve ceiling scores with 3 common patient-reported outcome measures.

BACKGROUND: Legacy shoulder outcome scores have postoperative ceiling scores effects when quantifying clinical outcomes for anatomic (aTSA) and reverse (rTSA) total shoulder arthroplasty patients. This study uses data from an international database of a single shoulder prosthesis using data from 30 different clinical sites to quantify and compare the percentage of aTSA and rTSA patients achieving postoperative ceiling scores with multiple outcome measures and defines the patient demographics, comorbidities, implant, and operative parameters associated with ceiling scores for each outcome measure. METHODS: Clinical outcomes for 1817 aTSA and 2635 rTSA patients between 2007 and 2019 were quantified with the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES), Simple Shoulder Test (SST), the University of California, Los Angeles (UCLA), Constant, and Shoulder Arthroplasty Smart (SAS) scores. The number of aTSA and rTSA patients with ceiling scores were calculated and sorted into those that achieved ceiling scores with the SST, ASES, and UCLA measures and compared to patients without ceiling scores. A univariate and multivariate analysis then identified the patient demographics, comorbidities, and implant and operative parameters associated with ceiling scores for each outcome measure. RESULTS: aTSA patients achieved ceiling scores at a significantly greater rate than rTSA patients for all outcome measures, except SAS. The SST score was the most susceptible to ceiling scores (aTSA = 43.4%, rTSA = 34.1%, P < .0001), followed by the ASES (aTSA = 23.7%, rTSA = 13.3%, P < .0001) and UCLA (aTSA = 22.2%, rTSA = 10.6%, P < .0001) scores. Ceiling scores were least likely with the Constant (aTSA = 0.4%, rTSA = 0%, P = .0060) and SAS (aTSA = 0.1%, rTSA = 0%, P = .0750) scores. Male patients had a significantly higher ceiling score rate than female patients using the SST and ASES scores, and no differences in ceiling score rates were observed with the UCLA, Constant, or SAS scores. Finally, we identified numerous patient demographic, comorbidity, implant, and operative parameters associated with SST, ASES, and UCLA ceiling scores for aTSA and rTSA patients. DISCUSSION: Postoperative ceiling scores occur at a high rate for aTSA and rTSA patients with the SST, ASES, and UCLA scores. Those most susceptible to ceiling scores are aTSA patients treated with cage glenoids, aTSA patients of lower body mass index, rTSA patients of male gender, rTSA patients with osteoarthritis diagnosis, and rTSA patients with subscapularis repair. Clinical researchers should consider using alternative scores, such as the SAS score, to ensure a more normalized distribution of data and more accurately quantify aTSA and rTSA outcomes.

Factors associated with improvement or loss of internal rotation after reverse shoulder arthroplasty.

BACKGROUND: Internal rotation (IR) with reverse total shoulder arthroplasty (rTSA) can be unpredictable. Identifying the factors associated with loss of or improved IR could aid preoperative patient counseling. This study quantifies the change in IR experienced by rTSA patients with nonfracture indications and identifies the patient, implant, and operative factors associated with IR loss or gain at 2-year minimum follow-up. METHODS: A total of 1978 primary rTSA patients were analyzed from an international database of a single rTSA prosthesis to quantify IR at 2 years' minimum follow-up. rTSA patients were divided into 2 cohorts based on their preoperative IR score, with group 1 patients having less active IR as defined by a preoperative IR score ≤3 and group 2 patients having greater active IR as defined by a preoperative IR score ≥4 (ie, L5 or higher). For both group 1 and 2 patients, univariate and multivariate analyses were performed to quantify the risk factors associated with IR loss after rTSA. RESULTS: Overall, 58.9% of rTSA patients experienced IR improvement and 17.0% lost IR after rTSA. The occurrence of IR loss or gain was dependent on preoperative IR score, as 73.2% of group 1 patients improved IR and only 40.1% of group 2 patients improved IR, whereas 31.0% of group 2 patients lost IR and only 6.3% of group 1 patients lost IR after rTSA. Numerous risk factors for IR loss were identified. For group 1 patients, male sex (P = .004, odds ratio [OR] = 2.056), tobacco usage (P = .004, OR = 0.348), larger humeral stem diameter (P = .008, OR = 0.852), and not having subscapularis repaired (P = .002, OR = 2.654) were significant risk factors for IR loss. For group 2 patients, male sex (P = .005, OR = 1.656), higher body mass index (P = .002, OR = 0.946), a diagnosis other than osteoarthritis (P < .001, OR = 2.189), nonaugmented baseplate usage (P < .001, OR = 2.116), and not having subscapularis repaired (P < .001, OR = 3.052) were significant risk factors for IR loss. CONCLUSION: The majority of patients improve IR after rTSA in the nonfracture setting. rTSA patients with substantial IR prior to surgery had a greater probability for losing IR compared to patients with poor preoperative IR. Numerous risk factors for IR loss were identified; these risk factors are useful for counseling patients considering rTSA, as some patients are more likely to lose IR than others.

Reverse Shoulder Arthroplasty Biomechanics.

The reverse total shoulder arthroplasty (rTSA) prosthesis has been demonstrated to be a viable treatment option for a variety of end-stage degenerative conditions of the shoulder. The clinical success of this prosthesis is at least partially due to its unique biomechanical advantages. As taught by Paul Grammont, the medialized center of rotation fixed-fulcrum prosthesis increases the deltoid abductor moment arm lengths and improves deltoid efficiency relative to the native shoulder. All modern reverse shoulder prostheses utilize this medialized center of rotation (CoR) design concept; however, some differences in outcomes and complications have been observed between rTSA prostheses. Such differences in outcomes can at least partially be explained by the impact of glenoid and humeral prosthesis design parameters, surgical technique, implant positioning, patient-specific bone morphology, and usage in humeral and glenoid bone loss situations on reverse shoulder biomechanics. Ultimately, a better understanding of the reverse shoulder biomechanical principles will guide future innovations and further improve clinical outcomes.

Deltoid fatigue part 2: a longitudinal assessment of anatomic total shoulder arthroplasty over time.

BACKGROUND: Gradual loss of overhead range of motion (ROM) has been observed after reverse shoulder arthroplasty (RSA). It remains unclear if this is caused by the effect of RSA design on muscle fiber lengthening or is part of the natural aging process of the shoulder musculature. Although studies have attempted to evaluate deltoid fatigue after RSA, there is a paucity of literature evaluating this effect after anatomic shoulder arthroplasty (aTSA), which would be expected to occur due to aging alone. The purpose of this study is to evaluate the effect of time on overhead ROM after aTSA and compare this with previous data on a similar cohort of RSAs. We hypothesized that overhead ROM would decrease gradually over time in both groups without differences between prosthesis types. METHODS: A retrospective review of 384 aTSAs without complications was performed over a 10-year period. All shoulders were treated for primary osteoarthritis using a single implant system. Patients were evaluated longitudinally at multiple postoperative time points. At least 1 follow-up visit was between 1 and 2 years postoperatively and another at least 5 years after surgery. ROM and patient reported outcome measures (PROMs) were evaluated using linear-mixed models for repeated measures. These results were compared with a previously evaluated cohort of 165 well-functioning RSAs analyzed using the same methodology. RESULTS: Primary aTSA shoulders were observed to lose 0.7° of abduction per year starting 1 year postoperatively (P = .001). Smaller losses were observed in external rotation (-0.3°/yr, P = .06) and internal rotation (-0.04/yr, P < .001). However, no significant losses were observed in forward elevation (P = .8). All PROMs diminished slowly over time, but these changes did not exceed the minimally clinically important difference when modeled over 10 years (Simple Shoulder Test -0.08/yr, P < .001; American Shoulder Elbow Surgeons -0.5/yr, P < .001; University of California Los Angeles Shoulder Score -0.2/yr, P < .001). When compared with a similarly analyzed cohort of RSAs, overhead ROM decreased at a slower rate in the aTSA cohort (abduction -0.7° vs. -0.8°/yr, P = .9; FE -0.06° vs. -0.8°/yr, P = .05). DISCUSSION: In the well-functioning aTSA, gradual loss of ROM occurs in all planes of motion except forward elevation. However, these losses are small and have little meaningful impact relative to minimally clinically important difference thresholds on PROMs. Progressive loss of abduction seen in both aTSA and RSA is likely secondary to aging of the periscapular and rotator cuff musculature. When compared with RSA, loss of motion after aTSA was statistically similar, calling into question the belief that RSA-induced deltoid fatigue leads to loss of overhead motion over time.

Deltoid fatigue: a longitudinal assessment of reverse shoulder arthroplasty over time.

BACKGROUND: Studies evaluating the mid-term performance of reverse shoulder arthroplasty (RSA) have identified a drop in the Constant-Murley score between 6 and 8 years after surgery, which is most affected by a loss of forward elevation and strength. Alterations of the deltoid length and moment arm after RSA lead to nonphysiological stress on the deltoid muscle. Concern has arisen that the long-term implications of increased deltoid work may be causing "deltoid fatigue." The purpose of this study was to evaluate the long-term effects of RSA on overhead range of motion (ROM) and validate the hypothesis of deltoid fatigue. METHODS: We performed a retrospective review of 165 RSAs over a 5-year period. Diagnoses were limited to cuff tear arthropathy, osteoarthritis with rotator cuff deficiency, and irreparable rotator cuff tear. All procedures were performed using a single implant system. Patients were evaluated longitudinally at multiple time points. They were required to undergo a minimum of 3 follow-up visits, with at least 1 visit at >5 years. ROM and patient-reported outcome measures were evaluated using linear mixed models for repeated measures to evaluate changes in outcome measures over time. A secondary analysis was performed to assess the influence of patient demographic factors on observed changes in ROM and patient-reported outcome measures. RESULTS: Primary RSA shoulders were observed to lose 0.8° of forward elevation and abduction per year starting at 1 year postoperatively (P = .006), without a significant drop at mid-term follow-up. No significant change in external or internal rotation was observed. Male patients and patients with a diagnosis of osteoarthritis with rotator cuff deficiency showed greater baseline overhead ROM at 1 year postoperatively, but the subsequent rates of functional decline were similar regardless of age, sex, or indication. DISCUSSION: This study challenges the previous theory of deltoid fatigue resulting in a significant loss of overhead ROM beginning 6-8 years after index arthroplasty. However, a slower progressive decline in overhead ROM in well-functioning RSA shoulders was observed, averaging 0.8° of overhead ROM per year. This progressive deterioration occurs at a slightly greater rate than that observed in the natural shoulder. The observed rate of functional decline was found to be independent of age, sex, and preoperative diagnosis.