Impact of accumulating risk factors on the incidence of dislocation after primary reverse total shoulder arthroplasty using a medial glenoid-lateral humerus onlay prosthesis.

BACKGROUND: The aim of this study was to facilitate preoperative identification of patients at risk for dislocation after reverse total shoulder arthroplasty (rTSA) using the Equinoxe rTSA prosthesis (medialized glenoid, lateralized onlay humerus with a 145° neck-shaft angle) and quantify the impact of accumulating risk factors on the occurrence of dislocation. METHODS: We retrospectively analyzed 10,023 primary rTSA patients from an international multicenter database of a single platform shoulder prosthesis and quantified the dislocation rate associated with multiple combinations of previously identified risk factors. To adapt our statistical results for prospective identification of patients most at-risk for dislocation, we stratified our data set by multiple risk factor combinations and calculated the odds ratio for each cohort to quantify the impact of accumulating risk factors on dislocation. RESULTS: Of the 10,023 primary rTSA patients, 136 (52 female, 83 male, 1 unknown) were reported to have a dislocation for a rate of 1.4%. Patients with zero risk factors were rare, where only 12.7% of patients (1268 of 10,023) had no risk factors, and only 0.5% of these (6 of 1268) had a report of dislocation. The dislocation rate increased in patient cohorts with an increasing number of risk factors. Specifically, the dislocation rate increased from 0.9% for a patient cohort with 1 risk factor to 1.0% for 2 risk factors, 1.6% for 3 risk factors, 2.7% for 4 risk factors, 5.3% for 5 risk factors, and 7.3% for 6 risk factors. Stratifying dislocation rate by multiple risk factor combinations identified numerous cohorts with either an elevated risk or a diminished risk for dislocation. DISCUSSION: This multicenter study of 10,023 rTSA patients demonstrated that 1.4% of the patients experienced dislocation with one specific medialized glenoid-lateralized humerus onlay rTSA prosthesis. Stratifying patients by multiple combinations of risk factors demonstrated the impact of accumulating risk factors on the incidence of dislocation. rTSA patients with the greatest risk of dislocation were those of male sex, age ≤67 years at the time of surgery, patients with body mass index ≥31, patients who received cemented humeral stems, patients who received glenospheres having a diameter >40 mm, and/or patients who received expanded or laterally offset glenospheres. Patients with these risk factors who are considering rTSA using a medial glenoid-lateral humerus should be made aware of their elevated dislocation risk profile.

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.

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 5851 total shoulder arthroplasties (TSAs) including aTSA (n = 2236) and rTSA (n = 3615) 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.

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.

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.

Side-to-side differences in postoperative function and patient satisfaction after bilateral total shoulder arthroplasties.

BACKGROUND: As the number of anatomic and reverse total shoulder arthroplasty (TSA) procedures increase, there will be a natural increase in patients who undergo staged bilateral TSA procedures. Bilateral TSAs have been shown to improve patient outcomes; however, it is unknown whether these patients experience side-to-side differences in clinical outcomes and satisfaction between shoulders. Understanding these differences is imperative for accurate patient and provider expectations. METHODS: An international multicenter registry was used to identify patients who underwent staged bilateral TSAs from April 2007 to October 2019 with a minimum of 2-year follow-up. American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) outcomes and satisfaction ratings were compared between dominant and nondominant shoulders, and first and second arthroplasties. Side-to-side differences in postoperative ASES and unequal satisfaction ratings were also explored by using regression analyses to identify potential factors influencing these differences. RESULTS: A total of 60 patients (22 bilateral anatomic TSAs, 38 bilateral reverse TSAs) were identified for inclusion. Group analyses revealed that bilateral TSA patients demonstrated similar functional outcomes and satisfaction regardless of dominance and surgery sequence. Type of TSA, specifically bilateral reverse TSAs, significantly predicted greater side-to-side differences in postoperative ASES scores (P = .025), indicating reverse TSA patients demonstrated greater between-sides differences in postoperative functional outcomes compared with those undergoing anatomic TSAs. Additionally, a larger proportion of bilateral reverse TSA patients reported unequal satisfaction between shoulders (31.6%) compared with anatomic TSA patients (9.1%). Logistic regression analysis revealed that greater side-to-side differences in postoperative ASES scores were found to increase the likelihood of reporting unequal satisfaction between shoulders (odds ratio 1.11, P < .001), which may explain this outcome. CONCLUSIONS: Most patients who undergo bilateral TSAs can expect similar outcomes on both shoulders regardless of dominance and surgery sequence. However, we did find patients who had discordant results between shoulders. Those who underwent reverse TSAs more frequently reported unequal satisfaction with their TSA procedures, which is likely due to larger side-to-side differences in postoperative function. It is unclear why these differences occurred, but this information may be important for providers to remember when counseling these patients for accurate postoperative expectations.

Characterizing the trade-off between range of motion and stability of reverse total shoulder arthroplasty.

BACKGROUND: The trade-off between range of motion (ROM) and stability of reverse total shoulder arthroplasty (RSA) has long been hypothesized to exist but has not yet been well characterized. The goal of this study was to use design optimization techniques to obtain a Pareto curve, which quantifies the trade-off between 2 competing objectives and is defined by the performance of optimum designs that maximize one surgical outcome without sacrificing the other. METHODS: Multi-objective design optimization techniques were used; 4 design and surgical parameters including glenoid lateralization (GLat), neck-shaft angle (NSA), inferior offset of the center of rotation (CORinf), and humerus lateralization (HLat) were tuned simultaneously. The ROM and stability, the objectives to be optimized, of any candidate design were characterized computationally using a combination of finite element models, musculoskeletal models, analytical equations, and surrogate models. Optimum designs and Pareto curves were determined separately for a standard cup depth and a shallow cup depth. The performance of the optimum designs, in terms of ROM and stability, was compared with a representative commercially available design. RESULTS: A Pareto curve was obtained for each cup depth, confirming there is a trade-off between ROM and stability of RSA. In comparison to the commercially available design (cup depth, 8.1 mm; GLat, 5 mm; NSA, 155°; CORinf, 0 mm; HLat, 0 mm), the designs optimized for ROM offered 38.8% (cup depth, 6 mm; GLat, 16 mm; NSA, 163.6°; CORinf, 4 mm; HLat, 0.6 mm) and 35.2% (cup depth, 8.1 mm; GLat, 16 mm; NSA, 160.5°; CORinf, 4 mm; HLat, -0.2 mm) improvement in ROM. The designs optimized for stability (cup depth of 6 mm with GLat of 16 mm, NSA of 170°, CORinf of 4 mm, and HLat of 3 mm and cup depth of 8.1 mm with GLat of 16 mm, NSA of 170°, CORinf of 4 mm, and HLat of 3 mm) both offered 12.4% improvement in stability over the commercially available design. Designs in the toe region of the Pareto curve offered between 75% and 90% of the maximum possible improvement over the commercially available design for both objectives. CONCLUSION: It was confirmed that a trade-off exists between ROM and stability of RSA, in which maximizing one outcome requires a sacrifice in the other. The relative gains and sacrifices in the competing outcomes when traversing the Pareto front could aid in understanding clinically optimum designs based on patient-specific needs.

Comparison of complication types and rates associated with anatomic and reverse total shoulder arthroplasty.

BACKGROUND: Complications after anatomic (aTSA) and reverse (rTSA) total shoulder arthroplasty can be devastating to a patient's quality of life and require revisions that are costly to both the patient and the health care system. The purpose of this study is to determine the types, incidence, and timing of complications following aTSA and rTSA using an international database of patients who received a single-platform total shoulder arthroplasty system, in order to quantify the types of failure modes and the differences that occur between aTSA and rTSA. METHODS: A total of 2224 aTSA (male-female, 1090:1134) and 4158 rTSA (male-female, 1478:2680) patients were enrolled in an international database of primary shoulder arthroplasty performed by 40 different surgeons in the United States and Europe. Adverse events and revisions reported for these 6382 patients were analyzed to identify the most common failure modes associated for both aTSA and rTSA. RESULTS: For the 2224 aTSA patients, 239 adverse events were reported for a complication rate of 10.7% and 124 revisions for a revision rate of 5.6%. The top 3 complications for aTSA were rotator cuff tear/subscapularis failure (n = 69; complication rate = 3.1%, revision rate = 1.9%), aseptic glenoid loosening (n = 55; complication rate = 2.5%, revision rate = 1.9%), and infection (n = 28; complication rate = 1.3%, revision rate = 0.8%). For the 4158 rTSA patients, 372 adverse events were reported for a complication rate of 8.9% and 104 revisions for a revision rate of 2.5%. The top 3 complications for rTSA were acromial/scapular fracture/pain (n = 102; complication rate = 2.5%, revision rate = 0.0%), instability (n = 60; complication rate = 1.4%, revision rate = 1.0%), and pain (n = 49; complication rate = 1.2%, revision rate = 0.2%). CONCLUSIONS: This large database analysis quantified complication and revision rates for aTSA and rTSA. We found aTSA and rTSA complication rates of 10.7% and 8.9%, respectively; with revision surgery rates of 5.6% and 2.5%, respectively. The 2 most common complications for each prosthesis type (aTSA: subscapularis/rotator cuff tears, aseptic glenoid loosening; rTSA: acromial/scapular fractures, instability) were unique to each device. The rate of infection was similar for both. Future prosthesis and technique development should work to mitigate these common complication types in order to reduce their rate of occurrence.

Investigating the Effects of Demographics on Shoulder Morphology and Density Using Statistical Shape and Density Modeling.

A better understanding of how the shape and density of the shoulder vary among members of a population can help design more effective population-based orthopedic implants. The main objective of this study was to develop statistical shape models (SSMs) and statistical density models (SDMs) of the shoulder to describe the main modes of variability in the shape and density distributions of shoulder bones within a population in terms of principal components (PCs). These PC scores were analyzed, and significant correlations were observed between the shape and density distributions of the shoulder and demographics of the population, such as sex and age. Our results demonstrated that when the overall body sizes of male and female donors were matched, males still had, on average, larger scapulae and thicker humeral cortical bones. Moreover, we concluded that age has a weak but significant inverse effect on the density within the entire shoulder. Weak and moderate, but significant, correlations were also found between many modes of shape and density variations in the shoulder. Our results suggested that donors with bigger humeri have bigger scapulae and higher bone density of humeri corresponds with higher bone density in the scapulae. Finally, asymmetry, to some extent, was noted in the shape and density distributions of the contralateral bones of the shoulder. These results can be used to help guide the designs of population-based prosthesis components and pre-operative surgical planning.

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.

Planned Glenoid Implant Utilization: A Comparison of Preoperative Planning with and Without Computer-Assisted Navigation.

BACKGROUND: Preoperative planning for anatomic total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) is becoming increasingly common. While preoperative planning allows surgeons to determine individualized implant types, utilization of intraoperative navigation improves the accuracy of implant placement and may increase confidence in the preoperative plan. The purpose of this study was to evaluate and compare the rate at which surgeons use a glenoid implant different than their preoperative plan with and without the use of computer navigation. METHODS: A retrospective review of a multicenter prospectively collected shoulder arthroplasty database was conducted between 2016 and 2022. Inclusion criteria were primary aTSA or rTSA with an available preoperative plan and record of the actual implant used. Change in glenoid implant was defined as a deviation in the final implant from the preoperative plan in regard to backside shape (nonaugmented vs augment or differing augment shape). RESULTS: We included 1,915 shoulder arthroplasties (525 aTSA, 1,390 rTSA) performed with preoperative planning and intraoperative navigation and 110 shoulder athroplasties (37 aTSA, 73 rTSA) performed with preoperative planning alone. Overall, the final glenoid implant deviated from the preoperative plan less frequently when intraoperative navigation was used compared with preoperative planning alone (1.9% [n = 36] versus 7.3% [n = 8], P = 0.002). When stratified by procedure, deviation from the preoperative plan occurred significantly less for rTSA when preoperative planning was used with intraoperative navigation versus planning alone (2% [n = 29] versus 11% [n = 8], P < 0.001; OR = 0.17 [95% CI = 0.07 to 0.46]), but not aTSA (1% [n = 7] versus 0% [n = 0], P = 1). Use of intraoperative navigation was independently associated with lower odds of deviation from the preoperative plan on multivariable logistic regression (OR = 0.25 [95% CI = 0.11 to 0.56], P = 0.001). CONCLUSION: Use of intraoperative navigation is associated with increased adherence to the preoperative plan for primary rTSA. Use of navigation may increase surgeon confidence despite known limitations of glenoid visualization during this procedure. This may offer advantages in outpatient surgery centers and smaller hospitals where inventory space may be limited. LEVEL OF EVIDENCE: Ⅲ, retrospective cohort study.

Anatomic Versus Reverse Total Shoulder Arthroplasty for Primary Osteoarthritis With an Intact Rotator Cuff: A Midterm Comparison of Early Top Performers.

BACKGROUND: Several surgeons state that their best anatomic total shoulder arthroplasty (aTSA) outperforms their best reverse total shoulder arthroplasty (rTSA) when performed for rotator cuff-intact glenohumeral osteoarthritis. We identified the top-performing aTSAs and rTSAs at short-term follow-up and compared their clinical performance at midterm follow-up to validate this common claim. METHODS: A retrospective review of a multicenter shoulder arthroplasty database was conducted. All shoulders undergoing primary aTSA or rTSA for rotator cuff-intact glenohumeral osteoarthritis between 2007 and 2020 were reviewed. Shoulders with a follow-up clinical visit between 2 and 3 years and a clinical follow-up of minimum 5 years were included. Two separate cohorts were identified: patients with a top 20% (1) American Shoulder and Elbow Surgeons (ASES) score and (2) Shoulder Arthroplasty Smart (SAS) score at 2 to 3 years of follow-up. Clinical outcomes including range of motion, outcome scores, and rates of complications and revision surgeries were compared at minimum 5-year follow-up. RESULTS: The ASES score cohort comprised 185 aTSAs (mean age 67 years, 42% female) and 49 rTSAs (mean age 72 years, 45% female). The SAS score cohort comprised 145 aTSAs (mean age 67 years, 59% female) and 42 rTSAs (mean age 71 years, 57% female). Active external rotation (ER) was greater after aTSA at midterm follow-up in both ASES and SAS score cohorts; however, preoperative to postoperative improvement was equivalent. Postoperative ER and SAS scores were greater after aTSA in both cohorts (P < 0.05); however, no other significant differences in any preoperative or postoperative clinical outcomes were present (P > 0.05), and patients achieved the minimal clinically important difference and substantial clinical benefit at similar rates for all outcomes. No difference was found in the incidence of complications and revision surgeries between top-performing aTSAs and rTSAs. CONCLUSION: Among top-performing shoulder arthroplasties at early follow-up, aTSA does not appear to outperform rTSA, except superior ER at midterm follow-up. LEVEL OF EVIDENCE: Retrospective comparative cohort study, Level Ⅲ.

Implications of humeral short-stem diametral sizing on implant stability.

Background: Shoulder arthroplasty humeral stem design has evolved to include various shapes, coatings, lengths, sizes, and fixation methods. While necessary to accommodate patient anatomy characteristics, this creates a surgical paradox of choice. The relationship between the surgeon's selection of short-stem implant size and construct stiffness, resistance to subsidence and micromotion has not been assessed. Methods: Eight paired cadaveric humeri were reconstructed with surgeon-selected (SS) and 2-mm diametrically larger (SS+2) short-stemmed press-fit implants. Each reconstruction was subjected to 2000 cycles of 90° forward flexion loading, and stem subsidence and micromotion were measured using optical tracking. Compressive stiffness of the stem-bone reconstruction was then assessed by applying a load in-line with the stem axis that resulted in 5 mm of stem subsidence. Results: Increasing stem size by 2 mm resulted in the construct stiffness more than doubling compared to SS stems (-741 ± 243 N/mm vs. -334 ± 120 N/mm; P = .003; power = 0.971). These larger stems also subsided significantly less than their SS counterparts (SS: 1.2 ± 0.6 mm; SS+2: 0.5 ± 0.5 mm; P = .029; power = 0.66), though there were no significant changes in micromotion (SS: 169 ± 59 µm; SS+2: 187 ± 52 µm; P = .506; power = 0.094). Conclusions: The results of this study highlight the importance of proper short-stem sizing, as a relatively small 2 mm increase in diametral size was observed to significantly impact construct stiffness, which could increase the risk of stress shielding and implant loosening. Future work should focus on developing tools that objectively quantify bone quality and aid surgeons in selecting the appropriate size short-stem humeral implants for a particular patient.

Maximizing range of motion of reverse total shoulder arthroplasty using design optimization techniques.

Range of motion (ROM) obtained after reverse shoulder arthroplasty (RSA) is an important factor in patient satisfaction and success of the procedure. The optimum RSA design that maximizes ROM is currently unknown. Furthermore, it is unknown if the envelope of motion the RSA is optimized for (overall versus forward elevation planes only) will determine its design. We hypothesized that these were potentially competing objectives (maximizing ROM in frontal elevation planes would require sacrifice in posterior elevation planes), and as a result the optimized designs would differ. The objective of this study was to use computer models and design optimization techniques to determine RSA configurations optimized for either case and compare them in terms of design and performance. Design parameters included glenoid lateralization, humeral lateralization, neck-shaft angle, and inferior offset of the center of rotation (COR) and two different cup depths. All optimized designs maximized glenoid lateralization and inferior offset of the COR. Designs optimized specifically for greater forward elevation plane ROM, however, had slightly higher neck-shaft angles and greater humeral lateralization. In terms of performance, the optimized designs provided 31% to 39% increases in ROM in comparison to that of a representative commercially-available Grammot-style prosthesis. It was concluded that RSA designs optimized for overall versus forward elevation plane ROMs will differ, but both offer improvement over a representative commercially available design, regardless of which ROM region is considered.

Development and Application of a Novel Metric to Characterize Comprehensive Range of Motion of Reverse Total Shoulder Arthroplasty.

Active range of motion (ROM) of reverse total shoulder arthroplasty (rTSA) can be limited by bony impingement, muscle inability, and joint instability. The aim of this study was to develop a novel metric representative of comprehensive ROM of rTSA, which is evaluated in the context of all three factors. It was hypothesized that the metric, termed global circumduction ROM (GC-ROM), would capture differences resulting from directional changes in rTSA design parameters known to increase ROM. GC-ROM was calculated for a set of 18 rTSA configurations with humeral polyethylene cup depths of 6 and 8.1 mm, glenosphere lateralization (GLat) distances of 0, 5, and 10 mm, and neck-shaft angles (NSA) of 135°, 145°, and 155°. For any implant configuration, arm positions were defined by internal/external (IE) rotation angle and two spherical coordinates representing the elevation plane angle and elevation angle. At each IE rotation angle, incremental positions with variable elevation plane and elevation angles were checked for feasibility based on impingement, muscle ability, and risk of instability. Coordinates of feasible positions were mapped to unit spheres and connected to form regions, of which the surface area was calculated to represent allowable circumduction ROM. ROMs were averaged across all IE rotation angles to produce a single metric, GC-ROM. The results showed that decreasing cup depth and increasing GLat and NSA increased GC-ROM. In conclusion, a novel metric to characterize comprehensive ROM, evaluated based on several ROM-limiting factors, was developed as a performance metric through which rTSA designs can be compared. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:880-887, 2020.

Development and validation of a muscle wrapping model applied to intact and reverse total shoulder arthroplasty shoulders.

Assessment and optimization of procedural outcomes, namely joint replacement, that rely heavily on muscle action necessitates a model capable of accurately and reliably predicting muscle paths in an automated setting. In this study, such a model was developed and validated for the anatomic shoulder and one implanted with reverse total shoulder arthroplasty (rTSA), as these scenarios present particularly complex ranges of motion and wrapping geometries. A finite element (FE) element model included a "string-of-pearls" representation of the four rotator cuff muscles and the three deltoid muscle bundles. Muscle bundles consisted of 15 rigid spheres connected by linearly elastic springs and attached to the bones at their origins. The free ends of the muscle bundles were pulled to their insertions, after which motions were applied to the shoulder. Muscle moment arms were calculated and compared to data available in the literature qualitatively and using Pearson rho values and root-mean-square errors. The process was repeated following implantation of an rTSA. The FE model captured muscle paths throughout 180° of motion in under seven minutes. Moment arms at 30° and 60° of scaption generally fell within the ranges predicted by previous experimental and computational studies. The FE model showed good qualitative agreement with previously published results for abduction, flexion, and axial rotation before and after rTSA. In conclusion, a model capable of predicting muscle paths in the presence of variable wrapping geometry was developed and validated without sacrificing enough computational efficiency to render its use impossible in numerical techniques such as design optimization. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3308-3317, 2018.

Quantifying the competing relationship between adduction range of motion and baseplate micromotion with lateralization of reverse total shoulder arthroplasty.

Lateralizing the center of rotation (COR) of reverse total shoulder arthroplasty (rTSA) could improve functional outcomes and mitigate scapular notching, a commonly occurring complication of the procedure. However, resulting increases in torque at the bone-implant interface may negatively affect initial fixation of the glenoid-side component, especially if only two fixation screws can be placed. Shoulder-specific finite element (FE) models of four fresh-frozen cadaveric shoulders were constructed. Scapular geometry and material property distributions were derived from CT data. Generic baseplates with two and four fixation screws were virtually implanted, after which superiorly-oriented shear loads, accompanied by a compressive load, were applied incrementally further from the glenoid surface to simulate lateralization of the COR. Relationships between lateralization, adduction range of motion (ROM), the number of fixation screws and micromotion of the baseplate (initial implant fixation) were characterized. Lateralization significantly increases micromotion (p=0.015) and adduction ROM (p=0.001). Using two, versus four, baseplate fixation screws significantly increases micromotion (p=0.008). The effect of lateralization and the number of screws on adduction ROM and baseplate fixation is variable on a shoulder-specific basis. Trade-offs exist between functional outcomes, namely adduction ROM, and initial implant fixation and the negative effect of lateralization on implant fixation is amplified when only two fixation screws are used. The possibility of lateralizing the COR in order to improve functional outcomes of the procedure should be considered on a patient-specific basis accounting for factors such as availability and quality of bone stock.