Advances in Glenoid Design in Anatomic Total Shoulder Arthroplasty

Technological innovations in shoulder replacement: current concepts and the future of robotics in total shoulder arthroplasty

BACKGROUND

Total shoulder arthroplasty (TSA) has been rapidly evolving over the last several decades, with innovative technological strategies being investigated and developed in order to achieve optimal component precision and joint alignment and stability, preserve implant longevity, and improve patient outcomes. Future advancements such as robotic-assisted surgeries, augmented reality, artificial intelligence, patient-specific instrumentation (PSI) and other peri- and preoperative planning tools will continue to revolutionize TSA. Robotic-assisted arthroplasty is a novel and increasingly popular alternative to the conventional arthroplasty procedure in the hip and knee but has not yet been investigated in the shoulder. Therefore, the purpose of this study was to conduct a narrative review of the literature on the evolution and projected trends of technological advances and robotic assistance in total shoulder arthroplasty.

METHODS

A narrative synthesis method was employed for this review, rather than a meta-analysis or systematic review of the literature. This decision was based on 2 primary factors: (1) the lack of eligible, peer-reviewed studies with high-quality level of evidence available for review on robotic-assisted shoulder arthroplasty, and (2) a narrative review allows for a broader scope of content analysis, including a comprehensive review of all technological advances-including robotics-within the field of TSA. A general literature search was performed using PubMed, Embase, and Cochrane Library databases. These databases were queried by 2 independent reviewers from database inception through November 11, 2022, for all articles investigating the role of robotics and technology assistance in total shoulder arthroplasty. Inclusion criteria included studies describing "shoulder arthroplasty" and "robotics."

RESULTS

After exclusion criteria were applied, 4 studies on robotic-assisted TSA were described in the review. Given the novelty of this technology and limited data on robotics in TSA, these studies consisted of a literature review, nonvalidated experimental biomechanical studies in sawbones models, and preclinical proof-of-concept cadaveric studies using prototype robotic technology primarily in conjunction with PSI. The remaining studies described the technological advancements in TSA, including PSI, computer-assisted navigation, artificial intelligence, machine learning, and virtual, augmented, and mixed reality. Although not yet commercially available, robotic-assisted TSA confers the theoretical advantages of precise humeral head cuts for restoration of proximal humerus anatomy, more accurate glenoid preparation, and improved soft-tissue assessment in limited early studies.

CONCLUSION

The evidence for the use of robotics in total hip arthroplasty and total knee arthroplasty demonstrates improved component accuracy, more precise radiographic measurements, and improved early/mid-term patient-reported and functional outcomes. Although no such data currently exist for shoulder arthroplasty given that the technology has not yet been commercialized, the lessons learned from robotic hip and knee surgery in conjunction with its rapid adoption suggests robotic-assisted TSA is on the horizon of innovation. By achieving a better understanding of the past, present, and future innovations in TSA through this narrative review, orthopedic surgeons can be better prepared for future applications.

Anatomic glenohumeral arthroplasty: State of the art

Anatomical total shoulder arthroplasty in its modern form where it reproduces the normal shoulder has been utilized clinically for more than half a century. As the technology and the designs have changed to recreate the humeral and glenoid sides of the joint, the sophistication of design has resulted in the growing number of cases annually worldwide. This increase is due in part to the increasing number of indications that the prosthesis can treat with successful results. On the humeral side, there have been design changes to better reflect the proximal humeral anatomy, and humeral stems are increasingly placed safely without cement. Platform systems which allow conversion of a failed arthroplasty to a reverse configuration without stem extraction is another design change. Similarly, there has been increasing utilization of short stem and stemless humeral components. Extensive experience with shorter stem and stemless devices, however, has yet to demonstrate the purported advantages of these devices, as recent studies have demonstrated equivalent blood loss, fracture rates, operative times, and outcome scores. Easier revision with these shorter stems remains to be definitively established, with only one study comparing the ease of revision between stem types. On the glenoid side, hybrid cementless glenoids, inlay glenoids, cementless all-polyethylene glenoids, and augmented glenoids have all been investigated; however, the indications for these devices remain unclear. Lastly, innovative surgical approaches to implanting shoulder arthroplasty and the use of patient specific guides and computerized planning, while interesting concepts, still await validation before they are utilized on a widespread basis. While reverse shoulder arthroplasty has been increasingly used to reconstruct the arthritic shoulder, anatomic glenohumeral replacement maintains a significant role in the armamentarium of the shoulder surgeon.

Outcomes and survivorship of anatomic total shoulder arthroplasty: current concepts

Total shoulder arthroplasty (TSA) has been the gold standard of care for end-stage glenohumeral arthritis. Outcomes are varied and have been affected by both patient and implant characteristics. Patient factors, such as age, preoperative diagnosis, and preoperative glenoid morphology, can affect the outcomes after TSA. Similarly, the different glenoid and humeral component designs significantly affect the survivorship of TSA. Significant evolution has occurred in the design of the glenoid component with the aim of decreasing the glenoid-sided causes of failure in TSA. On the other hand, focus on the humeral component has been increasing as well, with a trend towards using shorter humeral stems. This article aims to look at the outcomes of TSA as affected by the various patient characteristics and design options for the glenoid and the humeral components. This review also aims to compare survivorship data from global literature and the Australian joint replacement registry and to provide insights into the implant combination that may provide the best patient outcome.

A comparison of pegged and keeled glenoid clinical outcomes at long-term follow-up after total shoulder arthroplasty

Background

The two main glenoid types used in total shoulder arthroplasty (TSA) are the pegged and keeled glenoid designs. We aimed to determine if a pegged glenoid is superior to a keeled glenoid at long-term follow-up as measured by range of motion (ROM), patient reported outcomes (PROs), and radiographic glenoid loosening.

Methods

We retrospectively reviewed all patients undergoing TSA by a single surgeon at an urban, academic hospital. The cohort was stratified into two groups based on glenoid type - one group consisting of keeled implants and a second group consisting of pegged implants. For each patient, forward elevation (FE), internal rotation (IR), external rotation (ER), visual analog scale (VAS), American Shoulder and Elbow Surgeons (ASES) shoulder score, and simple shoulder test (SST) scores were collected preoperatively and at the most recent follow-up visit. Radiographic variables included acromiohumeral interval (AHI) and glenoid loosening.

Results

After applying exclusion criteria, 144 TSAs were included in our study. Of these, 42 (29.2%) had keeled glenoids and 102 (70.8%) had pegged glenoids. Patients with a pegged glenoid implant were older (67.4 vs. 60.7 years; p < 0.001) and had a shorter follow-up time (9.3 vs. 14.4 years; p < 0.001) than patients with a keeled glenoid implant. At the most recent follow-up visit, there were no significant differences among postoperative FE, ER, AHI, or PROs. However, pegged glenoid implants provided significantly more internal rotation (T11 vs. L1; p = 0.010) and were less likely to show evidence of radiographic glenoid loosening (16.7% vs. 42.9%; p=<0.001). Revision rates were not significantly different between the pegged and keeled groups (6.9% vs. 14.3%; p = 0.158).

Conclusion

Although a pegged design correlated with superior internal rotation and less radiographic glenoid loosening, both pegged and keeled glenoid designs offered favorable long-term clinical outcomes following TSA over the long-term.

Innovations in Shoulder Arthroplasty

Innovations currently available with anatomic total shoulder arthroplasty include shorter stem designs and augmented/inset/inlay glenoid components. Regarding reverse shoulder arthroplasty (RSA), metal augmentation, including custom augments, on both the glenoid and humeral side have expanded indications in cases of bone loss. In the setting of revision arthroplasty, humeral options include convertible stems and newer tools to improve humeral implant removal. New strategies for treatment and surgical techniques have been developed for recalcitrant shoulder instability, acromial fractures, and infections after RSA. Finally, computer planning, navigation, PSI, and augmented reality are imaging options now available that have redefined preoperative planning and indications as well intraoperative component placement. This review covers many of the innovations in the realm of shoulder arthroplasty.

Glenohumeral osteoarthritis with intact rotator cuff treated with reverse shoulder arthroplasty: a systematic review

BACKGROUND

Although reverse shoulder arthroplasty (RSA) has shown satisfactory outcomes in rotator cuff-deficient shoulders, its performance in shoulders with an intact rotator cuff has not been fully elucidated. Shoulder osteoarthritis can present with alterations in glenoid morphology, which have contributed to inconsistent outcomes in anatomic shoulder replacement. The glenoid component is responsible for a predominance of these arthroplasty complications. Given these glenoid-related difficulties, RSA may provide a more favorable option. We aimed to summarize the current literature on rotator cuff intact osteoarthritis treated with primary RSA and to determine whether morphologic changes in the glenoid led to inferior outcomes.

METHODS

A literature search was performed using an inclusion criterion of primary RSA for osteoarthritis with an intact rotator cuff. The Modified Coleman Methodology Score was calculated to analyze reporting quality. Following appropriate exclusions, of the 1002 studies identified by the databases, 13 were selected.

RESULTS

Postoperative improvement in weighted means for Constant scores reached statistical significance (P = .02). The mean rate of major complications was 3.8%. A subset of 8 studies was created that detailed the following descriptions of altered glenoid morphology: "static posterior instability," "severe posterior subluxation," "posterior glenoid wear >20°," "significant posterior glenoid bone loss," "biconcave glenoid," "B2 glenoid," and "B/C glenoid." Within this subset, the mean complication rate was 4.7%, with 4 of the 7 studies having a rate ≤ 3%, and improvements in the Constant score (P = .002) and external rotation (P = .02) reached statistical significance.

DISCUSSION

RSA as treatment for osteoarthritis with an intact rotator cuff provides optimal outcomes with low complication rates across a short term of follow up. Preoperative considerations for using reverse arthroplasty in the treatment of osteoarthritis with an intact rotator cuff include glenoid retroversion, posterior humeral subluxation, and glenoid bone loss. The attributes of reverse arthroplasty that contribute to favorable outcomes in arthritic shoulders include its semiconstrained design and robust glenoid fixation. Soft-tissue imbalances as a consequence of pathologic glenoid morphology and chronic humeral subluxation can be mitigated with the RSA semiconstrained design. Glenoid bone loss can be effectively managed with RSA's robust glenoid fixation, with and without the use of bone graft. The capability to lateralize the joint center of rotation may be valuable when faced with a medialized glenoid wear pattern. The current findings suggest that reverse arthroplasty can achieve highly favorable outcomes for glenohumeral osteoarthritis with an intact rotator cuff.

Prevalence of Shoulder Arthroplasty in the United States and the Increasing Burden of Revision Shoulder Arthroplasty

Existing data on the epidemiology of shoulder arthroplasty are limited to future projections of incidence. However, the prevalence of shoulder arthroplasty (the number of individuals with a shoulder arthroplasty alive at a certain time and its implications for the burden of revision procedures) remains undetermined for the United States. Hence, the purpose of this study was to estimate the prevalence of shoulder arthroplasty in the United States.