Polyethylene wear in retrieved reverse total shoulder components

Modified notching classification in inverted-bearing and conventional-bearing reverse total shoulder arthroplasty

BACKGROUND

Scapular notching is a common complication of reverse total shoulder arthroplasty (RTSA). Although the notching rate has reduced significantly thanks to modifications to the surgical technique and humeral and glenoid components, uncontrollable polyethylene (PE)-induced osteolysis can still occur. In contrast to conventional-bearing (CB-RTSA), inverted-bearing RTSA (IB-RTSA) systems, with PE glenospheres and metal or ceramic humeral liners, avoid PE abrasion through scapulohumeral contact. If present, the resulting notch has a different size and configuration than with CB-RTSA. Thus, a modified notching classification seems reasonable. Even in CB-RTSA, the early stages of notching show a different configuration than implied by the established Nerot-Sirveaux classification; therefore, a modification of the classification system is recommended.

METHODS

In a prospective multicentre study, 250 cases underwent IB-RTSA. Of these, 39 died, and 28 were lost to follow-up for other reasons, leaving 183 shoulders for the final follow-up examination at a mean of 120.7 months (range 84.1-172.4 months). In the CB-RTSA group, we retrospectively evaluated radiographs of 59 consecutive patients with a follow-up ranging from 2 to 7 years. We analysed the appearance, evolution over time, and location of bone loss on the scapular neck according to the modified Nerot-Sirveaux classification.

RESULTS

In IB-RTSA, notching resulted in a new morphological configuration: In contrast to the Nerot-Sirveaux classification, notching began far from the baseplate as an impression or abrasion of the humeral component in the inferior scapular rim. Due to simultaneous mechanical ablation, the defect gradually enlarged, but usually did not contact the baseplate or extend beyond the inferior peg. No signs of PE-induced osteolysis were found. The notching rate reached 19% after 2 years and approached 36% after 10 years. Most shoulders had grade 0 notching (64%), followed by grade 1 (29%); extensive erosion (grade 4) was not observed. In the CB-RTSA group, a small bony impression or erosion without signs of PE-induced osteolysis was observed medial to the scapular neck, without contact with the metaglene in the early phase, which was similar to the impression of the humeral component in IB-RTSA. The notching rate was 86% for CB-RTSA.

CONCLUSIONS

A new classification was developed for IB-RTSA, which corresponds to the pathophysiological processes and is compatible with the existing Nerot-Sirveaux classification. Bone erosion in CB-RTSA is not adequately represented by the established classification in the early stages. For this reason, a supplement to the existing classification is presented.

LEVEL OF EVIDENCE

Level 4, Case Series, Treatment Study.

Defining the tipping point for revision reverse shoulder arthroplasty

Background

This study sought to characterize the tipping point values (the functional scores that patients deem dysfunctional enough to warrant surgery) for patients undergoing first revision reverse total shoulder arthroplasty (rTSA).

Methods

This study was a retrospective review of a prospectively collected single-institution database of patients undergoing first revision rTSA between August 2015 and December 2019. Tipping point evaluation utilized preoperative scores including the American Shoulder and Elbow Surgeons (ASES), raw and normalized Constant, Shoulder Pain and Disability Index (SPADI), Simple Shoulder Test (SST), and University of California-Los Angeles (UCLA) scores, and active range of motion including abduction, forward elevation (FE), external rotation (ER), and internal rotation score (IR) prior to elective revision rTSA.

Results

We included 125 revision rTSAs. Tipping points were 37.6 ASES score, 30.5 raw Constant score, 35.5 normalized Constant score, 68.1 SPADI, 3.7 SST, 13.2 UCLA score, 64° abduction, 69° FE, 23° ER, and 3.1 IR. Higher SST was found for older patients and patients with a lower body mass index. Lower abduction and FE tipping points were reported in patients undergoing revision rTSA for rotator cuff failure, unexplained pain, and implant wear.

Discussion

These tipping points can help surgeons counsel patients regarding when to undergo revision rTSA.

Level of evidence

Level III; retrospective cohort study; treatment study.

Isolation and characterisation of wear debris surrounding failed total ankle replacements

Aseptic loosening and osteolysis continue to be a short- to mid-term problem for total ankle replacement (TAR) devices. The production of wear particles may contribute to poor performance, but their characteristics are not well understood. This study aimed to determine the chemical composition, size and morphology of wear particles surrounding failed TARs. A recently developed wear particle isolation method capable of isolating both high- and low-density materials was applied to 20 retrieved periprosthetic tissue samples from 15 failed TARs of three different brands. Isolated particles were imaged using ultra-high-resolution imaging and characterised manually to determine their chemical composition, size, and morphology. Six different materials were identified, which included: UHMWPE, calcium phosphate (CaP), cobalt chromium alloy (CoCr), commercially pure titanium, titanium alloy and stainless steel. Eighteen of the 20 samples contained three or more different wear particle material types. In addition to sub-micron UHMWPE particles, which were present in all samples, elongated micron-sized shards of CaP and flakes of CoCr were commonly isolated from tissues surrounding AES TARs. The mixed particles identified in this study demonstrate the existence of a complex periprosthetic environment surrounding TAR devices. The presence of such particles suggests that early failure of devices may be due in part to the multifaceted biological cascade that ensues after particle release. This study could be used to support the validation of clinically-relevant wear simulator testing, pre-clinical assessment of fixation wear and biological response studies to improve the performance of next generation ankle replacement devices. STATEMENT OF SIGNIFICANCE: Total ankle replacement devices do not perform as well as total hip and knee replacements, which is in part due to the relatively poor scientific understanding of how they fail. The excessive production of certain types of wear debris is known to contribute to joint replacement failure. This is the first study to successfully isolate and characterise high- and low-density wear particles from tissues collected from patients with a failed total ankle replacement. This article includes the chemical composition and characteristics of the wear debris generated by ankle devices, all of which may affect their performance. This research provides clinically relevant reference values and images to support the development of pre-clinical testing for future total ankle replacement designs.

Do total shoulder arthroplasty implants corrode?

BACKGROUND

Total shoulder arthroplasty (TSA) has become the gold-standard treatment to relieve joint pain and disability in patients with glenohumeral osteoarthritis who do not respond to conservative treatment. An adverse reaction to metal debris released due to fretting corrosion has been a major concern in total hip arthroplasty. To date, it is unclear how frequently implant corrosion occurs in TSA and whether it is a cause of implant failure. This study aimed to characterize and quantify corrosion and fretting damage in a single anatomic TSA design and to compare the outcomes to the established outcomes of total hip arthroplasty.

METHODS

We analyzed 21 surgically retrieved anatomic TSAs of the same design (Tornier Aequalis Pressfit). The retrieved components were microscopically examined for taper corrosion, and taper damage was scored. Head and stem taper damage was quantitatively measured with a non-contact optical coordinate-measuring machine. In selected cases, damage was further characterized at high magnifications using scanning electron microscopy. Energy-dispersive x-ray spectroscopy and metallographic evaluations were performed to determine underlying alloy microstructure and composition. Comparisons between groups with different damage features were performed with independent-samples t tests; Mann-Whitney tests and multivariate linear regression were conducted to correlate damage with patient factors. The level of statistical significance was set at P < .05.

RESULTS

The average material loss for head and stem tapers was 0.007 mm3 and 0.001 mm3, respectively. Material loss was not correlated with sex, age, previous implant, or time in situ (P > .05). We observed greater volume loss in head tapers compared with stem tapers (P = .002). Implants with evidence of column damage had larger volumetric material loss than those without such evidence (P = .003). Column damage aligned with segregation bands within the alloy (preferential corrosion sites). The average angular mismatch was 0.03° (standard deviation, 0.0668°), with negative values indicating distal engagement and positive values indicating proximal engagement. Implants with proximal engagement were significantly more likely to have column damage than those with distal engagement (P = .030).

DISCUSSION

This study has shown not only that the metal components of TSA implants can corrode but also that the risk of corrosion can be reduced by (1) eliminating preferential corrosion sites and (2) ensuring distal engagement to prevent fluid infiltration into the modular junction.

No Difference in Range of Motion in Reverse Total Shoulder Arthroplasty Using Standard or Constrained Liners: A Matched Cohort Study

Background

Prosthetic instability is one of the most common short-term complications following reverse total shoulder arthroplasty (RTSA). Numerous strategies exist to attempt to mitigate this complication, including utilization of constrained polyethylene humeral liners. A concern of constrained humeral liners is that they may come at the expense of restricted rotational range of motion (ROM). The purpose of the present study is to compare range of ROM and patient-reported outcomes (PROs), and satisfaction among matched cohorts using constrained vs. unconstrained liners after RTSA.

Methods

A multicenter shoulder arthroplasty registry was retrospectively reviewed to identify patients with two-year clinical follow-up after RTSA with constrained liners used at the surgeon’s discretion. All patients had the same inlay humeral prosthesis with a 135° neck shaft angle. This study cohort was matched 1:2 to control patients who underwent RTSA with standard liners based on age, sex, total glenoid-sided lateralization, glenosphere diameter, and surgery performed on the dominant arm. Improvement in PROs and ROM was compared between groups.

Results

Twenty-two patients were identified who underwent RTSA with a constrained humeral liner; these were compared to 44 matched patients with standard liners. The groups were found to have no notable differences in demographics, baseline PROs and ROM. At two years postoperatively, both cohorts demonstrated improvements in all PROs without statistically significant differences between the two groups. There were no differences between groups in improvement in any ROM measure, including forward flexion (constrained: 54^°, standard: 57^°, P = .771), external rotation at the side (constrained: 42°, standard: 41°, P = .906) or internal rotation at 90^° of abduction (constrained: 24^°, standard: 20^°, P = .587).

Conclusions

For an inlay humeral prosthesis with a 135^° neck shaft angle, utilization of a constrained liner for RTSA demonstrates no significant difference in ROM or PROs compared to a well-matched cohort of patients who underwent RTSA with a standard polyethylene humeral liner. These are reassuring data for using constrained liners when there is intraoperative concern for prosthetic instability.

Return of Scapulohumeral Rhythm in Patients After Reverse Shoulder Arthroplasty: A Midterm Stereoradiographic Imaging Analysis

BACKGROUND

Reverse shoulder arthroplasty (RSA) is associated with high rates of midterm complications including scapular notching, implant wear, and mechanical impingement. Scapulo-humeral rhythm (SHR), described by Codman in the 1920's, is defined as the ratio of glenohumeral motion to scapulothoracic motion. SHR is used as an indicator of shoulder dysfunction, as alterations in SHR can have profound implications on shoulder biomechanics. The determination of SHR can be hindered by soft-tissue motion artifacts and high radiation burdens associated with traditional surface marker or fluoroscopic analysis. EOS low dose stereoradiographic imaging analysis utilizing 3D model construction from a 2D X-ray series may offer an alternative modality for characterizing SHR following RSA.

METHODS

Patients (n=10) underwent an EOS imaging analysis to determine SHR at six and twelve months post-RSA. Leveraging 3D models of the implants, 2D/3D image registration methods were used to calculate relative glenohumeral and scapulothoracic positioning at 60, 90 and 120° of shoulder elevation. Subject-specific SHR curves were assessed and midterm changes in post-RSA SHR associated with follow-up time and motion phase were evaluated. Pearson correlations assessed associations between patient-specific factors and post-RSA SHR.

RESULTS

Mean post-RSA SHR was 0.81:1 across subjects during the entire midterm postoperative period. As a cohort, post-RSA SHR was more variable for 60-90° of shoulder motion. SHR for 90-120° of motion decreased (0.43:1) at twelve months post-RSA. Post-RSA SHR could be categorized using three relative motion curve patterns, and was not strongly associated with demographic factors such as BMI. 50% of subjects demonstrated a different SHR relative motion curve shape at twelve months post-RSA, and SHR during the 90120° of motion was found to generally decrease at twelve months.

CONCLUSION

Midterm post-RSA SHR was successfully evaluated using EOS technology, revealing lower SHR values (i.e., greater scapulothoracic motion) compared to normal values reported in the literature. SHR continued to change for some subjects during the midterm post-RSA period, with the greatest change during 90-120° of shoulder motion. Study findings suggest that future post RSA rehabilitation efforts to address elevated scapulothoracic motion may benefit from being patient-specific in nature and targeting scapular stabilization during 90-120° of shoulder motion. Level of Evidence: IV.

Backside polyethylene wear in reverse shoulder arthroplasty

BACKGROUND

Aseptic loosening from implant-associated osteolysis in reverse shoulder arthroplasty (RSA) may contribute to premature implant failure. Although articular side polyethylene (PE) damage has been well documented in the literature, no studies to date have investigated backside wear in RSA. The aims of this investigation were to (1) document and compare the damage between the backside and articular surface in explanted RSA components, (2) assess whether certain quadrants have a greater propensity for damage, and (3) report the most common mode(s) of backside PE damage.

METHODS

Twenty-one RSA humeral liners retrieved during revision procedures between 2005 and 2014 were included for analysis. The mean time between implantation and extraction was 16 months (10 days-88 months). Diagnoses at the time of revision included dislocation (10), infection (4), mechanical failure (3), loosening (2), and unknown (2). Liners were examined under light microscopy (×10-30 magnification) and damage on the articular and backside of the liner surface was graded using the modified Hood score. The location and damage modality were compared between the articular side and backside of the implant.

RESULTS

Damage was noted on the articular surfaces of all 21 liners and on the backside surface of 20 liners. The total damage in all the quadrants was higher on the articular surface than on the backside of the component, with a mean difference in total quadrant damage scores of 11.74 ± 3.53 (P < .001). There was no difference in damage among the quadrants on the backside (P = .44) or the articular surface (P = .08). The articular side exhibited greater scratching, abrasion, and surface deformation than the backside (P < .001).

CONCLUSIONS

This short-term retrieval study demonstrated that backside PE damage occurs on the humeral component of RSA implants. There was greater damage to the articular side of the liner but wear to the backside was present in almost all liners. The clinical importance of backside wear in RSA and its overall contribution to PE particulate disease and osteolysis needs further investigation.

Lateralized versus nonlateralized reverse total shoulder arthroplasty

Throughout the history of reverse total shoulder arthroplasty, the extent of lateral offset has changed considerably from "too lateral" to "too medial" and has been lately swinging back towards a point somewhere in between. Nonlateralized designs minimize shear forces on the glenoid and decrease force required by the deltoid. Glenoid lateralization decreases impingement and scapular notching and improves range of motion. Humeral lateralization achieves a more anatomic position of the tuberosities while maintaining a nonlateralized center of rotation. Several factors play a role in choosing the extent of lateral offset and method of lateralization.

Wear and damage in retrieved humeral inlays of reverse total shoulder arthroplasty-where, how much, and why?

BACKGROUND

Polyethylene (PE) wear and material degradation have been reported as complications in reverse total shoulder replacements (rTSAs). In this regard, scapular notching is associated with more clinical complications. Therefore, the purposes of the study were to quantify the linear and volumetric wear, as a measure for the amount of removed material, and to qualitatively assess the PE damage modes to describe the material degradation in retrieved rTSA humeral PE inlays that contribute to failure of shoulder replacements. Furthermore, this study aimed to evaluate the effect of scapular notching on PE wear and rim damage of the humeral components.

METHODS

The total study population of 39 humeral inlays contains 2 cohorts that were used for the damage mode analysis and for the wear analysis, respectively. The extent and presence of wear damage modes in 5 defined zones were assessed by a grading system for all PE joint replacements. For quantitative wear analysis the most frequent design (n = 17) was chosen. Using a coordinate-measuring machine and postprocessing software, volumetric wear measurements for the retrieved humeral PE inlays were undertaken. Furthermore, prerevision radiographs were analyzed for scapular notching. Finally, retrieval findings were correlated with clinical and radiographic data to consider the effect of notching and to identify risk of failures for these prostheses.

RESULTS

Damage on the rim of the humeral PE inlays was more frequent and severe than on the intended articulation surface. Irrespective of the damage mode, the inferior rim zone sustained the greatest amount of wear damage followed by the posterior zone. Burnishing, scratching, pitting, and embedded particles are most likely to occur in the articular surface area, whereas surface deformation, abrasion, delamination and gross material degradation are predominantly present in the inferior and posterior rim zones. The retrieved inlays exhibited a mean volumetric wear rate of 296.9 mm³/yr ± 87.0 mm³/yr. However, if the notched and non-notched components were compared, a significant higher volumetric wear rate (296.5 ± 106.1 mm³/yr) was found for the notched components compared to the non-notched group (65.7 ± 7.4 mm³/yr). Generally, there was a significantly greater incidence of damage and greater amount of wear if scapular notching occurred.

CONCLUSION

The notched components showed a 5-fold increase in PE wear rate. Therefore, scapular notching has a strong effect on PE damage and wear. If scapular notching can be clinically avoided, the PE wear performance is in a similar magnitude as found for hip and knee replacements.

Prosthetic Bearing Surfaces in Anatomic and Reverse Total Shoulder Arthroplasty

Total shoulder arthroplasty (TSA) and reverse TSA have provided an effective treatment for glenohumeral osteoarthritis; however, longevity of the procedure may be limited by osteolysis and polyethylene wear. In TSA, glenoid component failure occurs through several mechanisms, the most common being aseptic loosening and polyethylene wear. Newer bearing surfaces such as highly cross-linked ultra-high-molecular-weight polyethylene, vitamin E processing, ceramic heads, and pyrolytic carbon surfaces have shown improved wear characteristics in biomechanical and some early clinical studies. The purpose of this review is to provide a historical perspective and current state of the art of bearing surface technology in anatomic and reverse TSA.

Long-term impact of scapular notching after reverse shoulder arthroplasty

BACKGROUND

Because it medializes the centre of rotation, one of the drawbacks of reverse shoulder arthroplasty (RSA) is the risk of impingement between the humerus and lateral border of the scapula resulting in scapular notching. The long-term impact of this notching is not well known, either on function or the risk of glenoid loosening. The aim of this longitudinal study was to analyze the drawbacks of this notching.

METHODS

Between 1993 and 2006, 81 patients (91 shoulders) underwent RSA for primary glenohumeral osteoarthritis or massive cuff tear with or without osteoarthritis. This cohort was followed longitudinally with post-operative assessments done at one to two  years (T1), three to eight  years (T2), and nine+ years (T3). Before T3, 25 patients had died, nine were lost to follow-up, five  had the implants changed, and seven  had incomplete records. Thus, 45 shoulders were available for follow-up beyond nine years (mean follow-up of 12 years) and were used to determine the long-term impact of notching. Survival curves were generated using the occurrence of Sirveaux grade 3 or 4 notching and the presence of aseptic glenoid loosening as endpoints.

RESULTS

The survivorship before grade 3 or 4 notching developed was 83% at five years, 60% at 10 years, and 43% at 15 years. In the end, aseptic glenoid loosening occurred in four shoulders, all of which had developed grade 4 notching. No glenoid loosening occurred in the population with grade 0, 1, 2, or 3 notching (p = 0.02). The Constant score significantly decreased between T2 and T3, although it was not different between shoulders with and without advanced notching.

CONCLUSIONS

Beyond the second year post-RSA, the number of shoulders with grade 3 or 4 notching increases steadily up to the longest follow-up. Grade 4 notching always preceded the occurrence of late glenoid loosening. The functional outcomes become significantly worse after the 9th year post-RSA, although they were not correlated to the presence of high-grade scapular notching.

Analysis of the surface topography of retrieved metal-on-polyethylene reverse shoulder prostheses

Despite the encouraging short- and medium-term clinical results and increased usage of reverse shoulder replacements, a higher revision rate is documented compared with other major joint arthroplasties. Adverse reaction to polyethylene wear debris is still an important factor which may influence the long-term survival of reverse shoulder arthroplasty. To date, only a small number of retrieval studies of reverse shoulder arthroplasty have reported the different damage modes on polyethylene components, but none have quantified the ex vivo surface roughness on both articulating surfaces. The main purpose of this study was to assess, for the first time, the surface roughness of 13 retrieved metal-on-polyethylene reverse shoulder replacements using a white light profilometre with nanometre resolution. Although no significant relationship was observed between the surface roughness values and patient variables, it was noted that half of the polyethylene components still showed their original machining marks, indicating little change in vivo and that the metallic humeral components in the reversed design configuration showed low values of surface roughness after their time in vivo.

In vivo volumetric and linear wear measurement of reverse shoulder arthroplasty at minimum 5-year follow-up

BACKGROUND

Reverse shoulder arthroplasty is quickly becoming the most frequently performed glenohumeral joint replacement. The purpose of this study was to evaluate the volumetric and linear wear rates of ultrahigh-molecular-weight polyethylene humeral liners in vivo at a minimum 5-year follow-up.

METHODS

Radiostereometric analysis was used to image 15 patients at terminal range of motion in forward flexion, abduction, external rotation, and internal rotation and with the arm at the side. The relative position and orientation of the glenosphere and polyethylene were identified for each arm position. The apparent intersection of the glenosphere into the polyethylene was recorded as wear. Mean volumetric and linear wear rates were recorded, and Pearson correlation coefficients were applied to the 36-mm liners to assess the relationship between the wear rate and term of service.

RESULTS

The mean reverse shoulder arthroplasty term of service at the time of imaging was 8 ± 1 years (range, 6-11 years). The mean volumetric and linear wear rates for the 36-mm liners (n = 13) were 42 ± 22 mm³/yr (r = 0.688, P = .009) and 0.11 ± 0.03 mm/yr (r = 0.767, P = .002), respectively. The mean volumetric and linear wear rates for the 42-mm liners (n = 2) were 114 ± 44 mm³/yr and 0.17 ± 0.01 mm/yr, respectively. No single arm position was able to capture all recorded wear individually.

CONCLUSION

This study showed volumetric and linear wear rates of approximately 40 mm³/yr and 0.1 mm/yr, respectively, for the 36-mm polyethylene liners. The 42-mm liners showed higher wear rates, although a greater number of subjects is required for conclusive results. In vivo wear of reverse total shoulder arthroplasty is multidirectional and perceptible.

Humeral-sided Radiographic Changes Following Reverse Total Shoulder Arthroplasty

Background

We sought to characterize humeral-sided radiographic changes at a minimum of 2 years after reverse shoulder arthroplasty (RSA) to determine their association with specific implantation techniques.

Methods

The immediate and most recent postoperative anteroposterior radiographs of 120 shoulders with primary RSA and a minimum of 2-years of radiographic follow-up were analyzed (mean follow-up 35.2 months). Stress shielding was evaluated by measuring cortical thickness at 4 different locations. Three independent examiners evaluated radiographs for humeral osteolysis, radiolucent lines, stress shielding, stem loosening, and scapular notching.

Results

The cortical diameter, marker of external stress shielding, significantly decreased from initial to most recent measurement (P<0.001), but did not differ between cemented and uncemented groups. Cemented stems had significantly more osteolysis and radiolucent lines; uncemented stems had significantly more internal stress shielding (P<001). The presence of scapular notching was significantly correlated with the presence of humeral osteolysis (P<0.001). Three (2.5%) stems were deemed "at risk" for loosening and 2 (1.7%) were loose.

Conclusion

Cemented humeral stems were associated with an increased rate of radiolucent lines and osteolysis, whereas uncemented stems were associated with more internal stress shielding. Humeral cortical thickness significantly decreased over time regardless of fixation. There was an association between scapular notching and increased humeral osteolysis.

Failed Reverse Shoulder Arthroplasty and Recommendations for Revision

PURPOSE OF REVIEW

The most common complications warranting revision consideration in reverse shoulder arthroplasty (RSA) include instability and its associated causes: infection, periprosthetic fracture, and glenoid baseplate loosening. Management of complications can be challenging and the nuances of treatment are still being elucidated. The focus of this paper is to review the treatment of the failed RSA and discuss evidence-based recommendations for revision.

RECENT FINDINGS

The most common complications requiring revision RSA are instability and infection. The causes for instability can be subdivided into three main subcategories: loss of compression, loss of containment, and impingement. Loss of compression is further broken down into 6 subcategories revolving around abnormal prosthesis positioning, undersized prostheses, or intrinsic soft-tissue tension loss leading to instability. Periprosthetic infection can also lead to instability, yet the most appropriate management for infected RSA remains controversial. Restoring stability by maximizing deltoid and soft tissue tension while avoiding impingement revolves around three basic methods: (1) lateralizing and/or upsizing the glenosphere to an inferior position on the glenoid, (2) use of a more constrained polyethylene insert, and (3) distalizing the humerus by increasing the polyethylene thickness and/or the thickness of the humeral tray. Management of periprosthetic joint infection can be performed in one-stage, two-stage, or "three-stage" procedures all showing good outcomes with two-stage procedures being the most commonly performed. However, persistent positive culture with propriobacterium acnes can occur in up to 25% of cases. In order to limit the associated morbidity from failed revision reverse shoulder arthroplasty, continued research on best management of associated complications is warranted.

Reverse shoulder arthroplasty with a cementless short metaphyseal humeral prosthesis without a stem: survivorship, early to mid-term clinical and radiological outcomes in a prospective study from an independent centre

INTRODUCTION

The use of reverse total shoulder arthroplasty has increased for the management of cuff-deficient glenohumeral joint arthritis and fractures. With bone preservation being a major target in reverse shoulder arthroplasty, metaphyseal humeral components without a stem were developed. The aim of this study is to present the survivorship, functional and radiological outcomes of a novel short metaphyseal prosthesis without a diaphyseal stem from an independent centre.

METHODS

Clinical function and radiological features of patients undergoing stemless reverse shoulder arthroplasty were prospectively recorded. Patients' demographics, indications for surgery, complications, functional and radiological assessment at the final follow-up as well as survivorship with the end point of revision for any reason were recorded.

RESULTS

Between 2009 and 2016, 36 patients received 37 reverse shoulder arthroplasties with the stemless Verso prosthesis. Mean age of the patients was 76.9 years. The most common indication for surgery was cuff tear arthropathy. Mean follow-up was 3 years (range 1-7 years). Oxford shoulder score improved from an average of 11 pre-operatively (range 2-19) to 44 post-operatively (range 29-48) (p < 0.0001). There was one case of a deep post-operative infection that needed washout, liner exchange with retention of the prosthesis. Radiographic analysis showed no lucencies, or stress shielding around the humeral or glenoid components. Constant score at the final follow-up was on average 63 (range 35-86). Activities of daily living with requirement for internal and external rotation score (ADLEIR) was on average 12 pre-operatively (range 0-27) and 31 post-operatively (range 18-36) (p < 0.0001). There was 100% survivorship of the prosthesis in this early to mid-term study.

CONCLUSION

This early to mid-term prospective study demonstrates excellent survivorship and radiological results of the Verso reverse shoulder replacement. It needs a simple reproducible technique, and the results have been replicated at an independent centre. This study underlines its survivorship in the early to mid-term and confirms lower incidence of complications such as instability, notching, loosening and the need for revision surgery. Most importantly, it conserves the humeral bone stock for revision arthroplasties in the future. Our results are similar to those of the currently published literature.

Validation of In Vivo Linear and Volumetric Wear Measurement for Reverse Total Shoulder Arthroplasty Using Model-Based Radiostereometric Analysis

Presently, polyethylene wear measurement of reverse total shoulder arthroplasty (rTSA) is restricted to in vitro, in silico, and retrieval analysis, with no method for the quantification of in vivo wear of well-functioning implants. The purpose of this study was to validate the use of model-based radiostereometric analysis (MBRSA) as a measurement tool for in vivo rTSA wear using a phantom setup. Six additively manufactured polyethylene inserts were fabricated, one unworn control and five to represent known wear patterns, and individually fit within the rTSA components. Each insert was imaged using standard radiostereometric techniques and analyzed using MBRSA. From the position and orientation estimation provided by MBRSA, a micro-computed tomography model of the control insert was virtually placed within the metaphyseal tray. The apparent intersection of the glenosphere into the insert was recorded as wear. This method enables wear measurements with a linear precision of 0.21 mm and a bias of 0.36 ± 0.13 mm, and a volumetric precision of 49.3 mm³ , with a bias of 48.9 ± 24.3 mm³ . This technique allows for the in vivo measurement of polyethylene wear without the requirement of marker beads or baseline radiographs, expanding the potential for in vivo wear measurements to larger populations and retrospective analysis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1620-1627, 2019.

The effect of combined loading cycles on the wear of reverse shoulder joint replacements

Wear of polyethylene is a current limitation in the long-term survival of reverse shoulder arthroplasties (RSAs). The purpose of this study was to investigate, for the first time, the influence of a combination of clinically relevant activities of daily living (ADLs) as patterns of motion and loading on the wear of ultra-high molecular-weight polyethylene (UHMWPE) in RSA. This physiological combined cycle, termed "repeated-motion-load", was applied on four new samples of a commercially available reverse shoulder prosthesis for five million cycles using the unique Newcastle Shoulder Wear Simulator. This resulted in a mean wear rate of 12.0 ± 3.9 mm³/million cycles for the UHMWPE components in combination with metallic glenospheres, while the average articulating UHMWPE surface roughness reduced from 692 ± 132 nm Sa to 42 ± 29 nm Sa.

The Influence of Different Rotator Cuff Deficiencies on Shoulder Stability Following Reverse Shoulder Arthroplasty

BACKGROUND

The primary indication for reverse shoulder arthroplasty (RSA) is rotator cuff arthropathy caused by a deficient rotator cuff. Cuff deficiency in patients is highly variable in its distribution and extent, with mechanical implications that may significantly affect post-operative recovery. This study investigated the effects of variable cuff deficiency on the propensity for impingement between the scapula and humeral component and resulting subluxation, the source of two common complications (scapular notching and instability).

METHODS

Five different finite element models of an RSA were analyzed with varying degrees of rotator cuff deficiency: (1) baseline, with intact subscapularis, infraspinatus and teres minor, (2) no subscapularis, (3) no subscapularis or infraspinatus, (4) no infraspinatus, and (5) no infraspinatus or teres minor. The supraspinatus was not included in any models, as it is absent in rotator cuff arthropathy. Each model was moved through a prescribed arc of 45° internal/ external rotation originating from neutral.

RESULTS

Greater rotator cuff deficiency was associated with more impingement and larger magnitudes of subluxation. The largest subluxation (7.5 mm) and highest impingement-related contact stress (479 MPa) was in the model lacking all rotator cuff muscle groups. Posterior subluxation was present in most models lacking the infraspinatus, while anterior subluxation was present in all models lacking the subscapularis.

CONCLUSIONS

This study helps clarify how different rotator cuff deficiencies influence shoulder stability following RSA and can ultimately help predict which patients may be at greater risk for impingement-related scapular notching and subluxation.

CLINICAL RELEVANCE

Surgeons should carefully consider the nature of the rotator cuff deficiency and its influence on impingement and instability when planning for RSA.Level of Evidence: V.

Quantitative evaluation of retrieved reverse total shoulder arthroplasty liner surface deviation and volumetric wear

Polyethylene wear is a known complication in total joint arthroplasty, however, in vivo wear rates in reverse total shoulder arthroplasty (RTSA) remain largely unknown. This study aimed to quantify volumetric and surface deviation changes in retrieved RTSA humeral liners using a novel micro-computed tomography (μCT)-based technique. After IRB-approval, 32 humeral liners (single manufacturer and model) with term-of-service greater than 90 days were analyzed. Clinical demographics and surgical data were collected via chart review. Unworn liners were used as geometric controls. Retrieved and unworn liners underwent μCT scanning. Retrieved liner volumes were isolated, co-registered to controls of matching geometry, and surface deviations of the articulation surface and rim were computed. Differences in total volume loss (TVL), volumetric wear rate (VWR), and surface deviation were reported. Semi-quantitative grading evaluated rim damage presence and severity. Mean term-of-service for all liners was 2.07 ± 1.33 years (range: 0.30-4.73). Mean TVL and VWR were 181.3 ± 208.2 mm³ and 114.5 ± 160.3 mm³ /year, respectively. Mean articulation and rim surface deviations were 0.084 ± 0.065 and 0.177 ± 0.159 mm, respectively. Articulation surface deviation was positively correlated to term-of-service. Rim damage was present on 63% of liners and correlated significantly to rim surface deviation. This study reports in vivo wear rates of retrieved RTSA implants. Our results demonstrate volumetric and articulation surface wear in select RTSA liners that is correlated to term-of-service. Calculation of in vivo wear rates can help bridge the gap between clinical outcomes and experimental models such as wear simulations and computational models. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2007-2014, 2018.

Classification of instability after reverse shoulder arthroplasty guides surgical management and outcomes

BACKGROUND

Revision of unstable reverse shoulder arthroplasty (RSA) remains a significant challenge. The purpose of this study was to determine the reliability of a new treatment-guiding classification for instability after RSA, to describe the clinical outcomes of patients stabilized operatively, and to identify those with higher risk of recurrence.

METHODS

All patients undergoing revision for instability after RSA were identified at our institution. Demographic, clinical, radiographic, and intraoperative data were collected. A classification was developed using all identified causes of instability after RSA and allocating them to 1 of 3 defined treatment-guiding categories. Eight surgeons reviewed all data and applied the classification scheme to each case. Interobserver and intraobserver reliability was used to evaluate the classification scheme. Preoperative clinical outcomes were compared with final follow-up in stabilized shoulders.

RESULTS

Forty-three revision cases in 34 patients met the inclusion for study. Five patients remained unstable after revision. Persistent instability most commonly occurred in persistent deltoid dysfunction and postoperative acromial fractures but also in 1 case of soft tissue impingement. Twenty-one patients remained stable at minimum 2 years of follow-up and had significant improvement of clinical outcome scores and range of motion. Reliability of the classification scheme showed substantial and almost perfect interobserver and intraobserver agreement among all the participants (κ = 0.699 and κ = 0.851, respectively).

DISCUSSION

Instability after RSA can be successfully treated with revision surgery using the reliable treatment-guiding classification scheme presented herein. However, more understanding is needed for patients with greater risk of recurrent instability after revision surgery.

The effect of humeral polyethylene insert constraint on reverse shoulder arthroplasty biomechanics

BACKGROUND

There is little information on the effects of altering reverse shoulder arthroplasty (RSA) polyethylene constraint on joint load, load angle and deltoid force. The present biomechanical study aimed to investigate the effects of changing RSA polyethylene constraint on joint load, load angle, deltoid force and range of motion.

METHODS

A custom RSA implant capable of measuring forces across the joint with varying polyethylene constraint was tested in six cadaveric shoulders. Standard-, low- and high-constraint (retentive) polyethylene liners were tested, and joint kinematics, loads and muscle forces were recorded.

RESULTS

When polyethylene constraint was altered, joint load and load angle during active abduction were not affected significantly (p > 0.19). Additionally, the force required by the deltoid for active abduction was not affected significantly by cup constraint (p = 0.144). Interestingly, active abduction range of motion was also not affected significantly by changes in cup constraint (p > 0.45).

CONCLUSIONS

Altering polyethylene cup constraint in RSA to enhance stability does not significantly alter resultant joint loads and deltoid forces. Surprisingly, terminal abduction range of motion was also not significantly different with varying cup constraint, indicating that terminal impingement may be tuberosity related rather than polyethylene.

Neer Award 2017: wear rates of 32-mm and 40-mm glenospheres in a reverse total shoulder arthroplasty wear simulation model

BACKGROUND

Larger glenosphere diameters have been used recently to increase prosthesis stability and impingement-free range of motion in reverse total shoulder arthroplasty. The goal of this study was to evaluate the rate of polyethylene wear for 32-mm and 40-mm glenospheres.

METHODS

Glenospheres (32 mm and 40 mm, n = 6/group) and conventional polyethylene humeral liners underwent a 5-million cycle (MC) wear simulation protocol. Abduction-adduction and flexion-extension motion profiles were alternated every 250,000 cycles. At each interval, mass loss was determined and converted to volume loss and wear rate. At 0, 2.5 MC, and 5 MC, liners were imaged using micro-computed tomography to determine surface deviation. White light interferometry was performed on liners and glenospheres at 0 and 5 MC to quantify surface roughness. Wear particle morphology was characterized by environmental scanning electron microscopy.

RESULTS

Total volume loss was significantly higher in 40-mm liners from 1.5 MC onward (P < .05). Overall, volumetric wear rate was significantly higher in 40-mm liners compared with 32-mm glenospheres (81.7 ± 23.9 mm³/MC vs. 68.0 ± 18.9 mm³/MC; P < .001). However, micro-computed tomography surface deviation results demonstrated increased linear penetration on 32-mm glenospheres compared with 40-mm glenospheres (0.36 ± 0.03 µm vs. 0.28 ± 0.01 µm; P = .002). Surface roughness measurements showed no difference for liners; however, increased roughness was noted for 40-mm glenospheres at 5 MC compared with 32 mm (P < .05).

CONCLUSION

Larger glenospheres underwent significantly greater polyethylene volume loss and volumetric wear rates, whereas smaller glenospheres underwent greater polyethylene surface deviations. The enhanced stability provided by larger glenospheres must be weighed against the potential for increased polyethylene wear.

The effect of glenoid component version and humeral polyethylene liner rotation on subluxation and impingement in reverse shoulder arthroplasty

BACKGROUND

A previously validated finite element modeling approach was used to determine how changes in glenoid component version and polyethylene liner rotation within the humeral component affect the arm abduction angle at which impingement between the inferior glenoid and the polyethylene liner occurs as well as the amount of subluxation generated by that impingement.

MATERIALS AND METHODS

Five glenoid component versions (5° anteversion; neutral; 5°, 10°, and 20° retroversion) and 7 polyethylene liner rotations (20° and 10° anterior; neutral; 10°, 20°, 30°, and 40° posterior) were considered, resulting in 35 different clinically representative models. The humerus was internally and externally rotated and extended and flexed, and the resulting impingement and subluxation were measured. To further analyze more global trends and to identify implantations least prone to subluxation, polyethylene liner rotation was additionally varied in coarser 30° increments across the entire 360° range.

RESULTS

All subluxation caused by impingement occurred during external rotation and extension, and external rotation produced nearly 10-fold more subluxation than extension. Neutral glenoid component version was associated with the least amount of subluxation for all polyethylene liner rotations. Posteriorly rotated polyethylene liners, which place the thick inferior region of the component away from the scapula, produced the least amount of subluxation. The 90° and 120° posterior liner rotations produced no subluxation, whereas the 30° and 60° anterior liner rotations produced the greatest amount of subluxation.

CONCLUSION

These results indicate that rotating modern radially asymmetric humeral polyethylene liners posteriorly can reduce the risk of subluxation leading to dislocation and increase external rotation range of motion.

Analysis of polyethylene wear of reverse shoulder components: A validated technique and initial clinical results

One of the most prevalent phenomena associated with reverse total shoulder arthroplasty (rTSA) is scapular notching. Current methods examine only the damage to the scapula and no methods are available for quantifying the total wear volume of the polyethylene humeral bearing. Quantifying the polyethylene material loss may provide insight into the mechanism for scapular notching and into the particle dose delivered to the patient. A coordinate measurement machine (CMM) and custom computer algorithms were employed to quantify the volumetric wear of polyethylene humeral bearings. This technique was validated using two never-implanted polyethylene humeral liners with a controlled amount of wear in clinically relevant locations. The technique was determined to be accurate to within 10% of the known value and within 5 mm³ of the gravimetrically determined values. Following validation, ten retrieved polyethylene humeral liners were analyzed to determine a baseline for future clinical tests. Four of the ten polyethylene humeral liners showed visible and measureable wear volumes ranging from 40 to 90 mm³ total with a maximum wear rate as high as 470 mm³ /year in one short duration and significantly damaged humeral liner. This validated technique has the potential to relate patient outcomes such as scapular notching grades to polyethylene release into the body. While the total wear volumes are less than reported in literature for cases of osteolysis in knee and hip patients, dosages are well within the osteolytic thresholds that have been suggested, indicating that osteolysis may be a clinical concern in the shoulder. This work provides the basis for future studies that relate volumetric wear to patient outcomes. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:980-987, 2017.

Reverse shoulder arthroplasty for massive irreparable rotator cuff tears and cuff tear arthropathy: a systematic review

PURPOSE

To report the outcomes and complications of reverse shoulder arthroplasty (RSA) in massive irreparable rotator cuff tears (MIRCT) and cuff tear arthropathy (CTA).

METHODS

A systematic review of the literature contained in Medline, Cochrane, EMBASE, Google Scholar and Ovid databases was conducted on May 1, 2016, according to PRISMA guidelines. The key words "reverse total shoulder arthroplasty" or "reverse total shoulder prostheses" with "rotator cuff tears"; "failed rotator cuff surgery"; "massive rotator cuff tears"; "irreparable rotator cuff tears"; "cuff tear arthropathy"; "outcomes"; "complications" were matched. All articles reporting outcomes and complications of RSA for the management of MIRCT or CTA were included. The comparison between preoperative and postoperative clinical scores, as well as range of motion (ROM), was performed using the Wilcoxon-Mann-Whitney test. P values lower than 0.05 were considered statistically significant.

RESULTS

Seven articles were included in our qualitative synthesis. A statistically significant improvement in all clinical scores and ROM was found comparing the preoperative value with the postoperative value. The degrees of retroversion of the humeral stem of the RSA do not influence the functional outcomes in a statistically significant fashion. There were 17.4% of complications. The most frequent was heterotopic ossification, occurring in 6.6% of patients. Revision surgery was necessary in 7.3% of patients.

CONCLUSIONS

RSA restores pain-free ROM and improves function of the shoulder in patients with MIRCT or CTA. However, complications occur in a high percentage of patients. The lack of level I studies limits the real understanding of the potentials and limitations of RSA for the management of MIRCT and CTA.

Towards standardised definitions of shoulder arthroplasty complications: a systematic review of terms and definitions

INTRODUCTION

A transparent, reliable and accurate reporting of complications is essential for an evidence-based evaluation of shoulder arthroplasty (SA). We systematically reviewed the literature for terms and definitions related to negative events associated with SA.

MATERIALS AND METHODS

Various biomedical databases were searched for reviews, clinical studies and case reports of complications associated with SA. Any general definition of a complication, classification system, all reported terms related to complications and negative events with their definitions were extracted. Terms were grouped and organised in a hierarchical structure. Definitions of negative events were tabulated and compared.

RESULTS

From 1086 initial references published between 2010 and 2014, 495 full-text papers were reviewed. Five reports provided a general definition of the term "surgical complication" and 29 used a classification system of complications. A total of 1399 extracted terms were grouped based on similarities and involved implant or anatomical parts. One hundred and six reports (21.4%) defined at least one negative event for 28 different terms. There were 64 definitions related to humeral or glenoid loosening, and 25 systems documenting periprosthetic radiolucency. Other definitions considered notching, stress shielding, implant failure and tuberosity malposition.

CONCLUSIONS

A clear standardised set of SA complication definitions is lacking. Few authors reported complications based on definitions mainly considering radiological criteria without clinical parameters. This review should initiate and support the development of a standardised SA complication core set.

A Critical Review on Prosthetic Features Available for Reversed Total Shoulder Arthroplasty

Reversed total shoulder arthroplasty is a popular treatment in rotator cuff arthropathy and in displaced proximal humeral fractures in elderly. In 2016, 29 models of commercially available designs express this popularity. This study describes all the different design parameters available on the market. Prosthetic differences are found for the baseplate, glenosphere, polyethylene, and humeral component and these differences need to be weighed out carefully for each patient knowing that a gain in one mechanical parameter can balance the loss of another. Patient specific implants may help in the future.

Heterotopic ossification after reverse total shoulder arthroplasty

Aims

Heterotopic ossification (HO) occurs after arthroplasty, especially total hip arthroplasty. In this study we describe the incidence, evolution, morphology and clinical consequences of HO following reverse shoulder arthroplasty.

Patients and Methods

This is a single-centre retrospective study of 132 consecutive patients who received a Delta III or Delta Xtend reverse total shoulder arthroplasty between 2006 and 2013 for the treatment of cuff tear arthropathy. There were 96 women and 36 men. Their mean age at the time of surgery was 69 years (49 to 89) and the mean follow-up was 36 months (12 to 84). The incidence, evolution, morphology and clinical consequences of HO using the Constant-Murley score (CS) were analysed. A modified Brooker classification of HO of the hip was used.

Results

HO was seen in 39 patients (29.5%). A total of 31 of these patients (81.6%) began to develop HO by three months post-operatively. According to the Hamada classification, 11 patients had grade 1a, eight had grade 1b, six had grade 1c and 14 had grade 2 HO. The HO evolved over a mean of 8.3 months (3 to 21). Patients with HO had a lower mean CS at three (p = 0.017), six (p < 0.001) and 12 months (p < 0.001) post-operatively. HO was not associated with notching (p = 0.675).

Conclusion

HO after reverse shoulder arthroplasty is a non-progressive condition without long-term clinical consequences. Only grade 2 HO is clinically relevant with a negative effect on the function of the shoulder during its development. Cite this article: Bone Joint J 2016;98-B:1215–21.

Reverse shoulder arthroplasty with a cementless short metaphyseal humeral implant without a stem: clinical and radiologic outcomes in prospective 2- to 7-year follow-up study

BACKGROUND

Reverse shoulder prostheses are increasingly used in recent years for treatment of glenohumeral arthropathy with deficient rotator cuff. Bone preservation is becoming a major goal in shoulder replacement surgery. Metaphyseal humeral components without a stem were developed to minimize bone resection and preserve bone. This study evaluated the clinical and radiologic outcomes at 2 to 7 years using a novel short metaphyseal reverse total shoulder arthroplasty (rTSA) prosthesis without a diaphyseal stem.

METHODS

Between 2005 and 2010, 102 consecutive patients underwent rTSA with this implant, and 98 (20 men, 78 women) were available for follow-up. Mean age was 74.4 years (range, 38-93 years). Indications were cuff tear arthropathy, 65; fracture sequelae, 12; rheumatoid arthritis, 13; failed rotator cuff repair, 3; cuff deficiency with loosening of anatomic prosthesis, 3; and acute trauma, 2; with 17 of these as revisions.

RESULTS

Patients' satisfaction (Subjective Shoulder Value) improved from 8 of 100 to 85 of 100. The Constant score improved from 14 to 59 (age- and sex-adjusted, 86; P < .0001). Range of motion improved from 47° to 129° in elevation, 10° to 51° in external rotation, and 21° to 65° in internal rotation. Radiographic analysis showed no lucencies, subsidence, or stress shielding around the humeral or glenoid components. Glenoid notching was found in 21 patients (18 grade 1-2; 3 grade 3).

CONCLUSIONS

The short metaphyseal rTSA design without a diaphyseal stem shows encouraging short- to midterm results, with excellent pain relief and shoulder function, restoration of good active range of motion, and high patient satisfaction scores. The design of this implant seems to result in improved rotational movements, low incidence of glenoid notching, and no implant loosening, subsidence, or stress shielding.

Wear simulation strategies for reverse shoulder arthroplasty implants

Reverse total shoulder arthroplasty is a clinically accepted surgical procedure; however, its long-term wear performance is not known. The purpose of this work is to review wear simulator testing of reverse total shoulder arthroplasty, to develop a wear simulator protocol for reverse total shoulder arthroplasty, and to test it by performing a pilot study. The review of wear simulator testing in the literature revealed considerable variation in protocols. A combination of our own cadaveric testing and those of other research groups helped in determining the magnitude and direction of joint loading for the development of the present protocol. A MATCO orbital-bearing simulator was adapted using custom fixtures to simulate a circumduction motion of the shoulder under mildly adverse conditions, and a pilot study gave wear rates within the wide range found in the literature. Arguments were presented in support of the currently developed protocol, but it was also suggested that, rather than rely on one protocol, a series of simulator wear protocols should be developed to fully test the implant wear performance in reverse total shoulder arthroplasty.

Effect of size and dimensional tolerance of reverse total shoulder arthroplasty on wear: An in-silico study

Although huge research efforts have been devoted to wear analysis of ultra-high molecular weight polyethylene (UHMWPE) in hip and knee implants, shoulder prostheses have been studied only marginally. Recently, the authors presented a numerical wear model of reverse total shoulder arthroplasties (RTSAs), and its application for estimating the wear coefficient k from experimental data according to different wear laws. In this study, such model and k expressions are exploited to investigate the sensitivity of UHMWPE wear to implant size and dimensional tolerance. A set of 10 different geometries was analysed, considering nominal diameters in the range 36-42mm, available on the market, and a cup dimensional tolerance of +0.2, -0.0mm (resulting in a diametrical clearance ranging between 0.04-0.24mm), estimated from measurements on RTSAs. Since the most reliable wear law and wear coefficient k for UHMWPE are still controversial in the literature, both the Archard law (AR) and the wear law of UHMWPE (PE), as well as four different k expressions were considered, carrying out a total of 40 simulations. Results showed that the wear volume increases with the implant size and decreases with the dimensional tolerance for both the wear laws. Interestingly, different trends were obtained for the maximum wear depth vs. clearance: the best performing implants should have a high conformity according to the AR law but low conformity for the PE law. However, according to both laws, wear is highly affected by both implant size and dimensional tolerance, although it is much more sensitive to the latter, with up to a twofold variation of wear predicted. Indeed, dimensional tolerance directly alters the clearance, and therefore the lubrication and contact pressure distribution in the implant. Rather surprisingly the role of dimensional tolerance has been completely disregarded in the literature, as well as in the standards. Furthermore, this study notes some important issues for future work, such as the validation of wear laws and predictive wear models and the sensitivity of k to implant geometry.

Contact mechanics of reverse total shoulder arthroplasty during abduction: the effect of neck-shaft angle, humeral cup depth, and glenosphere diameter

BACKGROUND

Implant design parameters can be changed during reverse shoulder arthroplasty (RSA) to improve range of motion and stability; however, little is known regarding their impact on articular contact mechanics. The purpose of this finite element study was to investigate RSA contact mechanics during abduction for different neck-shaft angles, glenosphere sizes, and polyethylene cup depths.

METHODS

Finite element RSA models with varying neck-shaft angles (155°, 145°, 135°), sizes (38 mm, 42 mm), and cup depths (deep, normal, shallow) were loaded with 400 N at physiological abduction angles. The contact area and maximum contact stress were computed.

RESULTS

The contact patch and the location of maximum contact stress were typically located inferomedially in the polyethylene cup. On average for all abduction angles investigated, reducing the neck-shaft angle reduced the contact area by 29% for 155° to 145° and by 59% for 155° to 135° and increased maximum contact stress by 71% for 155° to 145° and by 286% for 155° to 135°. Increasing the glenosphere size increased the contact area by 12% but only decreased maximum contact stress by 2%. Decreasing the cup depth reduced the contact area by 40% and increased maximum contact stress by 81%, whereas increasing the depth produced the opposite effect (+52% and -36%, respectively).

DISCUSSION

The location of the contact patch and maximum contact stress in this study matches the area of damage seen frequently on clinical retrievals. This finding suggests that damage to the inferior cup due to notching may be potentiated by contact stresses. Increasing the glenosphere diameter improved the joint contact area and did not affect maximum contact stress. However, although reducing the neck-shaft angle and cup depth can improve range of motion, our study shows that this also has some negative effects on RSA contact mechanics, particularly when combined.

Elucidating trends in revision reverse total shoulder arthroplasty procedures: a retrieval study evaluating clinical, radiographic, and functional outcomes data

BACKGROUND

The purpose of this study was to explore relationships between damage modes in explanted reverse total shoulder arthroplasty (RTSA) components, patient and radiographic risk factors, and functional data to elucidate trends in RTSA failure.

METHODS

Fifty RTSA systems, retrieved from 44 patients, with 50 polyethylene (PE) liners, 30 glenospheres, 21 glenoid baseplates, 13 modular humeral metaphases, and 17 humeral stems, were examined for damage modes, including abrasion, burnishing, dishing, embedding, scratching, and pitting. PE liners were also analyzed for delamination and edge deformation. Charts were reviewed for patient, surgical, and functional data. Pre-revision radiographs were analyzed for scapular notching and loosening.

RESULTS

Average term of implantation was 20 months (range, 0-81 months). Metallic components exhibited abrasion, burnishing, dishing, pitting, and scratching. PE liners displayed all damage modes. Damage was exhibited on 93% of glenospheres and 100% of PE liners. Of 29 aseptic shoulders, 13 showed evidence of scapular notching and 5 of humeral loosening. There was a moderate correlation between radiographically observed implant failure or dissociation and PE embedding (r = 0.496; P < .001). There were weak and moderate correlations between scapular notching severity and PE dishing (r = 0.496; P = .006), embedding (r = 0.468; P = .010), and delamination (r = 0.384; P = .040).

CONCLUSIONS

To date, this is the largest series of retrieved RTSA components and the first to relate damage modes to radiographic and clinical data. Most damage was observed on the PE liners, on both the articular surface and rim, and glenosphere components. Correlation of retrieval findings with radiographic and clinical data may help establish predictors of prostheses at risk for failure.

Mechanical tradeoffs associated with glenosphere lateralization in reverse shoulder arthroplasty

BACKGROUND

Scapular notching in reverse shoulder arthroplasty occurs in up to 97% of patients. Notching is associated with decreased strength and reduced motion and may lead to long-term failure due to polyethylene wear. Many implant systems lateralize the glenosphere to address scapular notching, but the mechanical tradeoffs of lateralization have not been rigorously evaluated. We hypothesized that lateralization would decrease bony impingement but also decrease the mechanical advantage of the deltoid.

METHODS

Finite element models were created using the same implants with different amounts of glenoid lateralization: 5 mm of medialization to replicate glenoid erosion, as well as 2.5, 5, 7.5, and 10 mm of lateralization. Tests were performed with static and dynamic scapulae for motion in either the coronal or scapular plane. The angle of impingement between the scapula and the humeral polyethylene was recorded, as was the deltoid force required to elevate the arm.

RESULTS

Increasing lateralization decreased impingement while increasing the deltoid force required to elevate the arm. Differences were found between the static and dynamic scapulae, with the dynamic scapula model having increased humeral adduction before impinging. The impingement angle was also substantially affected by the bony prominences on the inferior scapula, showing how individual bony anatomy can affect impingement.

CONCLUSION

Lateralization is effective in increasing impingement-free range of motion but also increases the deltoid force required to perform identical tasks. In addition, impingement is determined by scapular motion, which should be included in all shoulder models.

Does lateralisation of the centre of rotation in reverse shoulder arthroplasty avoid scapular notching? Clinical and radiological review of one hundred and forty cases with forty five months of follow-up

PURPOSE

Our purpose was to evaluate the influence of metallic lateralisation of the centre of rotation (COR) in reverse shoulder arthroplasty (RSA) on the incidence of scapular notching and its eventual clinical and radiological consequences.

METHODS

We analysed 140 RSAs with a lateralised design (Arrow, FH Orthopedics, Mulhouse, France) implanted for massive rotator cuff tear with/without arthritis. Mean follow-up was 45 months (range 24-120, standard deviation 20). Patients were evaluated clinically using the Constant and Murley (Clin Orthop Relat Res 214:160-164, 1987) score and active range of motion (ROM) and radiologically using standard anteroposterior and axillary view. Scapular notching was assessed according to Sirveaux classification Simovitch et al. (J Bone Joint Surg Am, 89:588-600, 2007), and patients were separated into two groups (scapular notch/no scapular notch) and compared.

RESULTS

Forty-one notches (29 %) were found: 20 grade 1, 18 grade 2, and three grade 3. The latter three patients had a follow-up of 44, 70 and 84 months, respectively, and the scapular notch did not evolve in the final two years. Better pre-operative function was significantly associated with scapular notching (p < 0,05 for flexion and abduction), but no final clinical differences in ROM and Constant score were found between groups. A body mass index (BMI) <30 increased the risk of scapular notching, which was observed in 43 % of patients with a BMI < 30 and 30 % of patients with a BMI > 30 p = 0,048). Pre-operative narrowing of the subacromial space increased the risk of scapular notching, but age or gender showed no influence. However, there was a significantly greater number of scapular notches in patients operated on the dominant side (p = 0,04). No significant difference in lateral offset was found between groups (p = 0,99). Glenoid implantation in an excessively high position (p = 0,033) and absence of inferior tilt (p = 0,0029) were significantly associated with scapular notching.

CONCLUSIONS

In this series, metallic lateralisation of the COR in RSA did not impair clinical results, with patients achieving good flexion recovery ROM increase in rotations. Metallic lateralisation of the COR in RSA leads to a lower incidence of scapular notching (29 %) compared with previously reported results using other arthroplastic systems with a more medialised COR. However, although scapular notching was not totally eliminated, those that were found did not evolve over time. Several factors increased the incidence of scapular notching: BMI <30, better preoperative ROM, an excessively high glenoid implant and absence of inferior tilt.

Wear rates of retentive versus nonretentive reverse total shoulder arthroplasty liners in an in vitro wear simulation

BACKGROUND

Although short-term outcomes of reverse total shoulder arthroplasty (rTSA) remain promising, the most commonly cited complication remains prosthetic instability. A retentive rTSA liner is commonly used to increase system constraint; however, no studies have evaluated the rate of polyethylene wear. Our hypothesis was that more constrained retentive liners would have higher wear rates than nonretentive liners.

METHODS

Six nonretentive and six retentive rTSA non-cross-linked polyethylene liners were subjected to 4.5 million cycles of alternating cycles of abduction-adduction and flexion-extension motion loading profiles. The rTSA liners were assessed for gravimetric wear loss, 3-dimensional volumetric loss by novel micro-computed tomography analysis, and particulate wear debris analysis.

RESULTS

Volumetric wear rates were significant at 7 specific time points (1.0, 2.0, 2.5, 3.25, 3.75, 4.0, and 4.5 million cycles) throughout testing between nonretentive and retentive liners; however, overall mean volumetric wear rate was not statistically significant (P = .076). Total volume loss between liner test groups was found to be significant starting after 3.5 million cycles of testing. Maximum and mean surface deviations were found to be larger for retentive liners vs. nonretentive liners by micro-computed tomography analysis across the entire articulation surface.

DISCUSSION AND CONCLUSION

Retentive liners undergo significantly greater volume loss and greater surface deviation compared with nonretentive liners, most notably at later time points representing extended implantation times. Additional stability afforded by retentive liners should be balanced against the potential for increased wear and potential for subsequent polyethylene wear-induced aseptic loosening.

In vitro wear testing of a contemporary design of reverse shoulder prosthesis

Reverse shoulder arthroplasty is an increasingly common surgical intervention. However there are concerns and known limitations in relation to such joint replacement, while novel designs of reverse shoulder prostheses continue to appear on the market. Many claim to offer improvements over older designs but such assertions are difficult to validate when there is no consensus as to how such implants should be tested in vitro or even if such testing is necessary. In order to permit appropriate in vitro testing of reverse shoulder prostheses a unique, multi-station test rig was designed which was capable of applying motion in three axes to test prostheses. The shoulder simulator can apply up to 110° of motion in the flexion-extension and abduction-adduction axes and up to 90° in the internal-external rotation axis. Dynamic loading of up to 1500 N can be provided. The simulator is computer controlled so that the motions and loading associated with particular activities of daily living can be applied. A 4.5 million cycle wear test of commercially available reverse shoulder prostheses was undertaken using a 'mug to mouth' activity of daily living. Gravimetric analysis was used to characterise wear. After 4.5 million cycles of 'mug to mouth', the average wear rate of the test components was 14.3mm(3)/million cycles. Polyethylene test components showed a reduction in roughness and the median wear particle diameter was 167 nm. A three axis shoulder simulator has been designed and used to successfully test multiple samples of a commercially available reverse shoulder prosthesis.

Evaluation of a new baseplate in reverse total shoulder arthroplasty - comparison of biomechanical testing of stability with roentgenological follow up criteria

BACKGROUND AND PURPOSE

To minimize notching problem associated with reversed prostheses, inferior positioning of base plate is recommended. This reduces the risk of notching, but does not eliminate it completely. Both polyethylene/PE-induced osteolysis and implant-to-bone or implant-to-implant contact may still occur, contributing to the risk of screw-breakage and resulting long-term failure. Therefore, the stability and integration of a newly developed base plate without inferior screw and inversion of bearing materials was investigated.

PATIENTS AND METHODS

Biomechanical assessment of primary stability of the two types of glenoid baseplate (1- and 2-pegged) was carried out according to ASTM F-2028-02 (American Society for Testing and Materials). Patients with a follow-up period of at least 2 years were clinically (n=78) and for most of them radiologically (n=61) examined. The X-rays were evaluated for loosening and scapular notching.

RESULTS

The mean values of micromotions after 100,000 cycles showed no relevant differences between the 2-peg and the 1-peg base plates (47 μm for the 2-peg design and 43 μm for the 1-peg design), i.e. both were below the borderline for secure Osseointegration of 150 μm. Radiologically, no signs of loosening or radiolucent lines/RLL were found for both base plates. The mean incidence of inferior scapular notching was 23.6% (42 mm glenoid sphere: 15.8%). Only grade 1 and grade 2 notching was observed. Additionally as result of absence of PE-induced osteolysis shape, size, borderline and location of notching differed from those observed with conventional reverse total shoulder arthroplasty bearing materials.

CONCLUSION

In combination with modified inferior operating technique, the newly designed implant has the potential to reduce the incidence of scapular notching and to avoid both PE-induced osteolysis and metal-screw contact. The new design did not compromise stability of the base plate in any way during the investigation period, as demonstrated both by the data from the biomechanical investigation and also by the radiological follow-up.

LEVEL OF EVIDENCE

Level III, case-control study.

Wear rates of highly cross-linked polyethylene humeral liners subjected to alternating cycles of glenohumeral flexion and abduction

BACKGROUND

Although short-term outcomes of reverse total shoulder arthroplasty have been promising, long-term success may be limited due to device-specific complications, including scapular notching. Scapular notching has been explained primarily as mechanical erosion; however, the generation of wear debris may lead to further biologic changes contributing to the severity of scapular notching.

METHODS

A 12-station hip simulator was converted to a reverse total shoulder arthroplasty wear simulator subjecting conventional and highly cross-linked ultra-high-molecular-weight polyethylene humeral liners to 5 million cycles of alternating abduction-adduction and flexion-extension loading profiles.

RESULTS

Highly cross-linked polyethylene liners (36.5 ± 10.0 mm(3)/million cycle) exhibited significantly lower volumetric wear rates compared with conventional polyethylene liners (83.6 ± 20.6 mm(3)/million cycle; P < .001). The flexion-extension loading profile exhibited significantly higher wear rates for conventional (P < .001) and highly cross-linked polyethylene (P < .001) compared with the abduction-adduction loading profile. Highly cross-linked wear particles had an equivalent circle diameter significantly smaller than wear particles from conventional polyethylene (P < .001).

CONCLUSIONS

Highly cross-linked polyethylene liners significantly reduced polyethylene wear and subsequent particle generation. More favorable wear properties with the use of highly cross-linked polyethylene may lead to increased device longevity and fewer complications but must be weighed against the effect of reduced mechanical properties.

Reversed shoulder arthroplasty with inversed bearing materials: 2-year clinical and radiographic results in 101 patients

INTRODUCTION

This study documents 2-year clinical and radiographic results following reversed total shoulder arthroplasty using a novel prosthesis with inverted bearing materials (polyethylene glenoid; metal humeral component). This design was intended to avoid massive PE abrasion on the humeral side. Therefore, we predicted a lack of subsequent osteolysis-induced exacerbation of scapular notching, and because of other design features and modified operating technique a reduced notching rate.

MATERIALS AND METHODS

An ongoing, prospective, international, multicenter study of patients implanted with a novel prosthesis at six European centers. The current analysis presents 2-year follow-up data (patients operated between December 2007 and July 2009). Clinical evaluation tools comprised the Constant-Murley score (CS), the American Shoulder and Elbow Surgeon score, range of motion, and a visual analog scale to assess pain and satisfaction. Radiographs were evaluated for notching and radiolucent lines. Any complications were recorded.

RESULTS

In total, 113 prostheses (113 patients) with a mean follow-up of 27.6 (±3.6) months were analyzed. CS increased from 22.5 (±13.7) to 65.3 (±14.9) points (p = 0.06). Inferior scapular notching (only grade 1 and 2) was identified in 20.5 % of patients, with no signs of PE-induced osteolysis. 4.4 % of patients experienced an implant-related complication.

CONCLUSIONS

Inversion of the materials led to another type of notching with no signs of PE-induced osteolysis and no increase in the risk of short-term complications. Clinical results were comparable with other prostheses. Mid- to long-term results are required before any firm conclusions on clinical outcome and survival can be drawn.

Clinical, radiological, histological and retrieval findings of Activ-L and Mobidisc total disc replacements: a study of two patients

INTRODUCTION

This study evaluates the short-term clinical outcome, radiological, histological and device retrieval findings of two patients with second generation lumbar total disc replacement (TDR).

MATERIALS AND METHODS

The first patient had a single level L4-L5 Activ-L TDR, the second patient a L4-L5 Mobidisc and L5-S1 Activ-L TDR. The TDRs were implanted elsewhere and had implantation times between 1.3 and 2.8 years.

RESULTS

Plain radiographs and CT-scanning showed slight subsidence of the Activ-L TDR in both patients and facet joint degeneration. The patients underwent revision surgery because of recurrent back and leg pain. After removal of the TDR and posterolateral fusion, the pain improved. Histological examination revealed large ultrahigh molecular weight polyethylene (UHMWPE) particles and giant cells in the retrieved tissue surrounding the Mobidisc. The particles in the tissue samples of the Activ-L TDR were smaller and contained in macrophages. Retrieval analysis of the UHMWPE cores revealed evidence of minor adhesive and abrasive wear with signs of impingement in both TDR designs.

CONCLUSION

Although wear was unrelated to the reason for revision, this study demonstrates the presence of UHMWPE particles and inflammatory cells in second generation TDR. Long-term follow-up after TDR is indicated for monitoring wear and implant status.