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.

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.

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.