Effect of RSA glenoid baseplate central fixation on micromotion and bone stress

In silico analysis of rib force distribution in postscapulothoracic arthrodesis model

Scapulothoracic arthrodesis (STA) is carried out by fixing the scapula to thoracic ribs which in turn allows the patient suffering from Facioscapulohumeral Muscular Dystrophy to carry out shoulder-joint dependent activities of daily living. A biomechanical analysis of this procedure has not been conducted in the literature and, for the first time, this study investigates the finite element calculated glenohumeral-applied load distributions on ribs by creating a post-STA model. Three loading directions on the glenohumeral joint are designated: anterior-posterior, superior-inferior, and lateral-medial. Reaction forces on the ribs are calculated based on the glenoid force percent. Simulations are repeated by removing a singular rib contact to observe the change in force distributions in the case of missing levels or failed bonding as well as the impact of clavicle osteotomy. Total load distribution is observed highest at T2 followed by T3 and T6. In the T2 missing scenario, total loads on T3 and T4 increase. In the T4 missing case, the most affected level is T3. In the T6 missing scenario, total loads on T5 and T7 increase. In the clavicular osteotomy scenario, all levels' loads increase; the highest is recorded in T7 by 460%, followed by T5, T4, T2, T6, and T3. While all levels contribute to fixation strength, T2 is subjected to the highest loads, and, in the missing level scenarios, the loads are tolerated sufficiently by the remaining levels. Missing T4 scenario has the least effect on the system, which is interpreted as potentially the only skippable level of fixation. Clavicular osteotomy has the highest effect on the arthrodesis site.

How to avoid baseplate failure: the effect of compression and reverse shoulder arthroplasty baseplate design on implant stability

BACKGROUND

Failure to achieve fixation of the glenoid baseplate will lead to clinical failure. The fixation of the baseplate to the scapula must be able to withstand sufficient shear forces to allow bony ingrowth. The importance of compression to neutralize the forces at the baseplate-bone interface has been assumed to be critical in limiting excessive micromotion. The purpose of this study is to determine the effect of compression on implant stability with different baseplate designs.

METHODS

Various baseplate designs (1-piece monolithic central screw [1P], 2-piece locking central screw [2PL], and 2-piece nonlocking center screw [2PNL]) were investigated at 3 different compressive forces (high [810 N], medium [640 N], and low [530 N]). Synthetic bone cylinders were instrumented, and peripheral screws were used in all models. The combination of 1 locking and 3 nonlocking peripheral screw fixation was selected as worst-case scenario. Dynamic testing protocol followed the ASTM F2028-17 standard. The baseplate micromotion at high compression was compared to low compression. Additionally, the baseplate micromotion for each design was compared at baseline (first 50 cycles) and at 10,000 cycles for the 3 different compressive forces where motion above 150 μm was defined as failure.

RESULTS

Baseplate micromotion was found to negatively correlate with compression (rpb = -0.83, P < .0001). At baseline, all baseplate designs were considered stable, regardless of compression. With high compression, average micromotion at the glenoid baseplate-bone interface remained below the 150-μm threshold for all baseplate designs at 10,000 cycles (1P: 50 ± 10 μm; 2PL: 78 ± 32 μm; 2PNL: 79 ± 8 μm; P = .060). With medium compression, average micromotion at 10,000 cycles for all 3 designs remained below the 150-μm threshold (1P: 88 ± 22 μm; 2PL: 132 ± 26 μm; 2PNL: 107 ± 39 μm). The 2PL design had the highest amount of micromotion (P = .013). With low compression, both 2-piece designs had an average micromotion above the 150-μm threshold whereas the 1-piece design did not (1P: 133 ± 35 μm; 2PL: 183 ± 21 μm; 2PNL: 166 ± 39 μm). The 2PL design had significantly higher micromotion when compared to 1P design (P = .041).

DISCUSSION

The stability of a central screw baseplate correlates with the amount of compression obtained and is affected by implant design. For the same amount of compression, more micromotion is observed in a 2-piece design than a 1-piece design.

Stemless reverse humeral component neck-shaft angle has an influence on initial fixation

BACKGROUND

Stemless anatomic humeral components are commonly used and are an accepted alternative to traditional stemmed implants in patients with good bone quality. Presently, little literature exists on the design and implantation parameters that influence primary time-zero fixation of stemless reverse humeral implants. Accordingly, this finite element analysis study assessed the surgical implantation variable of neck-shaft angle, and its effect on the primary time-zero fixation of reversed stemless humeral implants.

METHODS

Eight computed tomography-derived humeral finite element models were used to examine a generic stemless humeral implant at varying neck-shaft angles of 130°, 135°, 140°, 145°, and 150°. Four loading scenarios (30° shoulder abduction with neutral forearm rotation, 30° shoulder abduction with forearm supination, a head-height lifting motion, and a single-handed steering motion) were employed. Implantation inclinations were compared based on the maximum bone-implant interface distraction detected after loading.

RESULTS

The implant-bone distraction was greatest in the 130° neck-shaft angle implantation cases. All implant loading scenarios elicited significantly lower micromotion magnitudes when neck-shaft angle was increased (P = .0001). With every 5° increase in neck-shaft angle, there was an average 17% reduction in bone-implant distraction.

CONCLUSIONS

The neck-shaft angle of implantation for a stemless reverse humeral component is a modifiable parameter that appears to influence time-zero implant stability. Lower, more varus, neck-shaft angles increase bone-implant distractions with simulated activities of daily living. It is therefore suggested that humeral head osteotomies at a higher neck-shaft angle may be beneficial to maximize stemless humeral component stability.

Reverse Shoulder Arthroplasty for Patients with Massive Rotator Cuff Tears or Cuff Tear Arthropathies at a Minimum Follow-up of 7 Years

Purpose

To evaluate indications and factors that influence long-term clinical outcomes and revision rates for reverse shoulder arthroplasty (RSA) in shoulders with irreparable massive rotator cuff tears (mRCTs) or cuff tear arthropathies (CTAs).

Methods

The authors retrospectively evaluated a consecutive series of shoulders with no fracture sequelae that underwent primary RSA between 2011 and 2013. Independent observers collected demographic data, surgical techniques, and implant types, as well as primary outcome measures such as American Shoulder and Elbow Society (ASES) score and Constant score (CS).

Study design

Case series, level IV.

Results

From the initial series of 123 patients that underwent RSA, 29 patients died (24%) for reasons unrelated to the shoulder arthroplasty, 11 were lost to follow-up (9%), and 4 required revision surgery (3%). The final cohort of 79 patients comprised 55 women (70%), and 24 men (30%), aged 72.7 ± 7.0. At a final follow-up of 8.9 ± 0.6 years (range: 7.4-10.3) the absolute CS was 59.0 ± 16.2, the age-/sex-adjusted CS was 76.6 ± 41.2, and ASES was 77.1 ± 20.3. Univariable analysis revealed no associations for absolute CS, but revealed that age-/sex-adjusted CS was significantly lower for patients with high blood pressure (β = -15.8, p = .025).

Conclusions

At a minimum follow-up of 7.4 years, the absolute CS was 59.0 ± 16.2, the age-/sex-adjusted CS was 87.4 ± 24.1 and ASES was 77.1 ± 20.3. When stratifying the outcomes of RSA by indication, there were no significant differences in patients with mRCTs versus CTA in terms of absolute CS, age-/sex-adjusted CS, and ASES. Univariable analysis revealed no association with absolute and age-/sex-adjusted CS for type of indication or surgical approach.

Considerations for Shoulder Arthroplasty Implant Selection in Primary Glenohumeral Arthritis With Posterior Glenoid Deformity

Glenoid deformity has an important effect on outcomes and complication rates after shoulder arthroplasty for primary glenohumeral arthritis. The B2/B3 glenoid has particularly been associated with a poorer outcome with shoulder arthroplasty compared with other glenoid types. One of the primary challenges is striking a balance between deformity correction and joint line preservation. Recently, there has been a proliferation of both anatomic and reverse implants that may be used to address glenoid deformity. The purpose of this review was to provide an evidence-based approach for addressing glenoid deformity associated with primary glenohumeral arthritis.

Pathogenesis, Evaluation, and Management of Osteolysis After Total Shoulder Arthroplasty

Radiographic osteolysis after total shoulder arthroplasty (TSA) remains a challenging clinical entity, as it may not initially manifest clinically apparent symptoms but can lead to clinically important complications, such as aseptic loosening. A thorough consideration of medical history and physical examination is essential to rule out other causes of symptomatic TSA—namely, periprosthetic joint infection—as symptoms often progress to vague pain or discomfort due to subtle component loosening. Once confirmed, nonoperative treatment of osteolysis should first be pursued given the potential to avoid surgery-associated risks. If needed, the current surgical options include glenoid polyethylene revision and conversion to reverse shoulder arthroplasty. The current article provides a comprehensive review of the evaluation and management of osteolysis after TSA through an evidence-based discussion of current concepts.

Central fixation element type and length affect glenoid baseplate micromotion in reverse shoulder arthroplasty

BACKGROUND

Reverse shoulder arthroplasty (RSA) is commonly used to treat patients with rotator cuff tear arthropathy. Loosening of the glenoid component remains one of the principal modes of failure and represents a significant complication that requires revision surgery. This study assessed the effects of various factors on glenoid baseplate micromotion for primary fixation of RSA.

MATERIALS AND METHODS

A half-fractional factorial design of experiment was used to assess 4 factors: central element type (central peg or screw), central cortical engagement according to length (13.5 or 23.5 mm), anterior-posterior peripheral screw type (nonlocking or locking), and cancellous bone surrogate density (160 or 400 kg/m³, 10 or 25 PCF). Glenoid baseplates were implanted into high- or low-density Sawbones rigid polyurethane foam blocks and cyclically loaded at 60° for 1000 cycles (500-N compressive force range) using a custom-designed loading apparatus. Micromotion at the 4 peripheral screw positions was recorded using linear variable differential transformers.

RESULTS

Central peg fixation generated 358% greater micromotion at all peripheral screw positions compared with central screw fixation (P < .001). Baseplates with short central elements that lacked cortical bone engagement generated 328% greater micromotion than those with long central elements (P = .001). No significant effects were observed when varying anterior-posterior peripheral screw type or bone surrogate density. There were significant interactions between central element type and length (P < .001).

DISCUSSION

A central screw and a long central element that engaged cortical bone reduced RSA baseplate micromotion. These findings serve to inform surgical decision making regarding baseplate fixation elements to minimize the risk of glenoid loosening and, thus, the need for revision surgery.

A Comparison of Central Screw versus Post for Glenoid Baseplate Fixation in Reverse Shoulder Arthroplasty Using a Lateralized Glenoid Design

The purpose of this study was to compare the short-term clinical and radiographic outcomes of a lateralized glenoid construct with either a central screw or post. Methods: A multicenter retrospective study was conducted of reverse shoulder arthroplasties (RSAs) with minimum 2-year clinical followup. All RSAs implanted had a 135° neck shaft angle (NSA) and a modular circular baseplate. The patients were divided into two cohorts based on the type of central fixation for their glenoid baseplates (central post (CP) vs. central screw (CS)). The clinical outcomes, rates of revisions, and available radiographs were evaluated. Results: In total, 212 patients met the study criteria. Postoperatively, both groups improved over their preoperative baseline. There were no significant differences between the cohorts in any PROs at 2 years postoperatively. No findings of gross loosening were identified in either cohort. Implant survival was 98.6% at 2 years. Conclusions: When using a lateralized glenoid implant with a 135° NSA inlay humeral component, both central post and central screw baseplate fixation provide good clinical outcomes, survivorship, and improvements in ROM at 2 years. There is no difference in loosening or revision rates between the types of baseplate fixation at a minimum of 2 years postoperatively.

Mechanical behavior of hybrid glenoid components compared to all-PE components: a finite element analysis

Purpose

The purpose of this finite element study was to compare bone and cement stresses and implant micromotions among all-polyethylene (PE) and hybrid glenoid components. The hypothesis was that, compared to all-PE components, hybrid components yield lower bone and cement stresses with smaller micromotions.

Methods

Implant micromotions and cement and bone stresses were compared among 4 all PE (U-PG, U-KG, A-KG, I-KG) and 2 hybrid (E-hCG, I-hPG) virtually implanted glenoid components. Glenohumeral joint reaction forces were applied at five loading regions (central, anterior, posterior, superior and inferior). Implant failure was assumed if glenoid micromotion exceeded 75 µm or cement stresses exceeded 4 MPa. The critical cement volume (CCV) was based on the percentage of cement volume that exceeded 4 MPa. Results were pooled and summarized in boxplots, and differences evaluated using pairwise Wilcoxon Rank Sum tests.

Results

Differences in cement stress were found only between the I-hPG hybrid component (2.9 ± 1.0 MPa) and all-PE keeled-components (U-KG: 3.8 ± 0.9 MPa, p = 0.017; A-KG: 3.6 ± 0.5 MPa, p = 0.014; I-KG: 3.6 ± 0.6 MPa, p = 0.040). There were no differences in cortical and trabecular bone stresses among glenoid components. The E-hCG hybrid component exceeded micromotions of 75 µm in 2 patients. There were no differences in %CCV among glenoid components.

Conclusions

Finite element analyses reveal that compared to all-PE glenoid components, hybrid components yield similar average stresses within bone and cement. Finally, risk of fatigue failure of the cement mantle is equal for hybrid and all-PE components, as no difference in %CCV was observed.

Level of evidence

IV, in-silico.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00494-8.

Finite element analysis to predict short and medium-term performance of the anatomical Comprehensive® Total Shoulder System

BACKGROUND

The number of Total Shoulder Arthroplasties (TSA) has increased in these last years with significant increase of clinical success. However, glenoid component loosening remains the most common cause of failure.

OBJECTIVE

In this study we evaluated the critical conditions to predict short and medium-term performance of the uncemented anatomical Comprehensive® Total Shoulder System using a finite element model that was validated experimentally.

METHODS

The finite element models of an implanted shoulder analysed included total shoulder components with pegs. The models were simulated in 3 phases of adduction: 45°, 60° and 90° to determine the most critical situation. Two different bone-implant fixation conditions were considered: post-surgery and medium term (2 years).

RESULTS

These show that the critical condition is for the shoulder in 90° adduction were the highest contact stress (70 MPa) was observed in the glenoid component. Relatively to the interface implant-bone strains, the maximum (-16000 µε) was observed for the short-term in the lateral region of the humerus. The highest micromotions were observed in the central fixation post of the glenoid component, ranging from 20 to 25 µm, and 325 µm in the lateral plane of the humeral component.

CONCLUSION

The predicted results are in accordance with clinical studies published and micromotions of the humeral component can be used to predict loosening and to differentiate shoulder implant designs.

Complications of Reverse Total Shoulder Arthroplasty: A Computational Modelling Perspective

Reverse total shoulder arthroplasty (RTSA) is an established treatment for elderly patients with irreparable rotator cuff tears, complex proximal humerus fractures, and revision arthroplasty; however, with the increasing indications for RTSA over the last decade and younger implant recipients, post-operative complications have become more frequent, which has driven advances in computational modeling and simulation of reverse shoulder biomechanics. The objective of this study was to provide a review of previously published studies that employed computational modeling to investigate complications associated with RTSA. Models and applications were reviewed and categorized into four possible complications that included scapular notching, component loosening, glenohumeral joint instability, and acromial and scapular spine fracture, all of which remain a common cause of significant functional impairment and revision surgery. The computational shoulder modeling studies reviewed were primarily used to investigate the effects of implant design, intraoperative component placement, and surgical technique on postoperative shoulder biomechanics after RTSA, with the findings ultimately used to elucidate and mitigate complications. The most significant challenge associated with the development of computational models is in the encapsulation of patient-specific anatomy and surgical planning. The findings of this review provide a basis for future direction in computational modeling of the reverse shoulder.

Reverse Shoulder Arthroplasty with Bony and Metallic versus Standard Bony Reconstruction for Severe Glenoid Bone Loss. A Retrospective Comparative Cohort Study

There are different techniques to address severe glenoid erosion during reverse shoulder arthroplasty (RSA). This study assessed the clinical and radiological outcomes of RSA with combined bony and metallic augment (BMA) glenoid reconstruction compared to bony augmentation (BA) alone. A review of patients who underwent RSA with severe glenoid bone loss requiring reconstruction from January 2017 to January 2019 was performed. Patients were divided into two groups: BMA versus BA alone. Clinical outcome measurements included two years postoperative ROM, Constant score, subjective shoulder value (SSV), and the American Shoulder and Elbow Surgeons Shoulder (ASES) score. Radiological outcomes included radiographic evidence of scapular complications and graft incorporation. The BMA group had significantly different glenoid morphology (p < 0.001) and greater bone loss thickness than the BA group (16.3 ± 3.8 mm vs. 12.0 ± 0.0 mm, p = 0.020). Both groups had significantly improved ROM (anterior forward flexion and external rotation) and clinical scores (Constant, SSV and ASES scores) at 2 years. Greater improvement was observed in the BMA group in terms of anterior forward flexion (86.3° ± 27.9° vs. 43.8° ± 25.6°, p = 0.013) and Constant score (56.6 ± 10.1 vs. 38.3 ± 16.7, p = 0.021). The BA group demonstrated greater functional and clinical improvements with higher postoperative active external rotation and ASES results (active external rotation, 49.4° ± 17.0° vs. 29.4° ± 14.7°, p = 0.017; ASES, 89.1 ± 11.3 vs. 76.8 ± 11.0, p = 0.045). The combination use of bone graft and metallic augments in severe glenoid bone loss during RSA is safe and effective and can be considered in cases of severe glenoid bone loss where bone graft alone may be insufficient.

Clinical and radiographic outcomes of reverse shoulder arthroplasty using a hybrid baseplate fixation mechanism

Background

Despite the success of reverse shoulder arthroplasty (RSA), complication rates remain high (13% to 25%), due to instability, infection, and glenoid component loosening, which can lead to revision. The aim of the present study was to report the early clinical outcomes of RSA using a new hybrid baseplate design, in comparison with the literature on other common RSA baseplates.

Methods

The authors retrospectively analyzed the records of 142 patients (142 shoulders) who underwent primary RSA using a hybrid baseplate design by the senior surgeons between May 2014 and December 2018. Preoperative and postoperative assessments included the Constant score (CS) and range of motion, including active forward elevation, external rotation, and internal rotation.

Results

Of the initial cohort of 142 patients, 13 were lost to follow-up (8.6%), 2 died (1.3%), and 8 required reoperations with implant removal (5.3%). The remaining 119 patients comprised 71 women (60%) and 48 men (40%), aged 73.6 ± 7.3 years at index surgery, 43 of whom required bony increased offset (36%). At a minimum follow-up of 2 years, the CS improved by 37.3 ± 16.1, active forward elevation increased by 51.2° ± 38.1°, external rotation increased by 16.4° ± 25.0°, and internal rotation increased by 1.5 ± 3.2.

Conclusion

At a minimum follow-up of 2 years after RSA using a new hybrid baseplate system, the CS and range of motion were satisfactory and comparable to those in recent systematic reviews. The findings of this study suggest that this hybrid baseplate system provides satisfactory outcomes in the short term, although longer follow-up studies are needed to validate its long-term efficacy.

Biomechanics of anatomic and reverse shoulder arthroplasty

The biomechanics of the shoulder relies on careful balancing between stability and mobility. A thorough understanding of normal and degenerative shoulder anatomy is necessary, as the goal of anatomic total shoulder arthroplasty is to reproduce premorbid shoulder kinematics.With reported joint reaction forces up to 2.4 times bodyweight, failure to restore anatomy and therefore provide a stable fulcrum will result in early implant failure secondary to glenoid loosening.The high variability of proximal humeral anatomy can be addressed with modular stems or stemless humeral components. The development of three-dimensional planning has led to a better understanding of the complex nature of glenoid bone deformity in eccentric osteoarthritis.The treatment of cuff tear arthropathy patients was revolutionized by the arrival of Grammont's reverse shoulder arthroplasty. The initial design medialized the centre of rotation and distalized the humerus, allowing up to a 42% increase in the deltoid moment arm.More modern reverse designs have maintained the element of restored stability but sought a more anatomic postoperative position to minimize complications and maximize rotational range of motion. Cite this article: EFORT Open Rev 2021;6:918-931. DOI: 10.1302/2058-5241.6.210014.