Optimizing glenosphere position and fixation in reverse shoulder arthroplasty, Part Two: The three-column concept

Ten technical aspects of baseplate fixation in reverse total shoulder arthroplasty for patients without glenoid bone loss: a systematic review

The aim of this systematic review was to collect evidence on the following 10 technical aspects of glenoid baseplate fixation in reverse total shoulder arthroplasty (rTSA): screw insertion angles; screw orientation; screw quantity; screw length; screw type; baseplate tilt; baseplate position; baseplate version and rotation; baseplate design; and anatomical safe zones. Five literature libraries were searched for eligible clinical, cadaver, biomechanical, virtual planning, and finite element analysis studies. Studies including patients >16 years old in which at least one of the ten abovementioned technical aspects was assessed were suitable for analysis. We excluded studies of patients with: glenoid bone loss; bony increased offset-reversed shoulder arthroplasty; rTSA with bone grafts; and augmented baseplates. Quality assessment was performed for each included study. Sixty-two studies were included, of which 41 were experimental studies (13 cadaver, 10 virtual planning, 11 biomechanical, and 7 finite element studies) and 21 were clinical studies (12 retrospective cohorts and 9 case-control studies). Overall, the quality of included studies was moderate or high. The majority of studies agreed upon the use of a divergent screw fixation pattern, fixation with four screws (to reduce micromotions), and inferior positioning in neutral or anteversion. A general consensus was not reached on the other technical aspects. Most surgical aspects of baseplate fixation can be decided without affecting fixation strength. There is not a single strategy that provides the best outcome. Therefore, guidelines should cover multiple surgical options that can achieve adequate baseplate fixation.

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.

Intraoperative navigation system use increases accuracy of glenoid component inclination but not functional outcomes in reverse total shoulder arthroplasty: a prospective comparative study

BACKGROUND

While the use of computer-assisted navigation systems in prosthetic implantation is steadily increasing, its utility in reverse shoulder arthroplasty (RSA) remains unclear. The purpose of this study was to evaluate the clinical utility of an intraoperative navigation system in patients undergoing RSA.

MATERIALS AND METHODS

Patients undergoing navigated or standard RSA at a single institution between September 2020 and December 2021 were prospectively enrolled. Exclusion criteria included noncompliance with study procedures or humeral fracture. Outcome measures included postoperative version and inclination, range of motion (ROM), complications, and patient-reported outcome measurements (PROMs: American Shoulder and Elbow Surgeons score [ASES], Disabilities of the Arm, Shoulder, and Hand score [DASH], Simple Shoulder Test [SST], and Visual Analog Scale [VAS]) at final follow-up.

RESULTS

The final cohort contained 16 patients with navigation and 17 with standard RSA at a mean follow-up of 16 months (range 12-18 months). Average age was 72 years (range 66-80 years), 8 male (24%) and 25 female (76%). There were no differences in demographics between groups (p > 0.05). At baseline, the navigated group had a greater proportion of Walch B1 and B2 glenoids (p = 0.04). There were no differences between groups regarding baseplate type and native/planned/postoperative glenoid version and inclination. In both groups, planned and postoperative versions were not significantly different (p = 0.76). Patients who did not have navigation demonstrated significant differences between planned and postoperative inclination (p = 0.04), while those with navigation did not (p = 0.09). PROM scores did not differ between groups at final follow-up for SST (p = 0.64), DASH (p = 0.38), ASES (p = 0.77), or VAS (p = 0.1). No difference in final ROM was found between groups (p > 0.05). Over 50% of all screws in both groups were positioned outside the second cortex (p = 0.37), albeit with no complications.

CONCLUSIONS

There were no statistically significant differences in ROM, PROMs, and satisfaction between patients receiving computer-navigated and standard RSA at a short-term follow-up. Despite more severe preoperative glenoid erosion in the navigated group, all patients were able to achieve an appropriate neutral axis postoperatively. The cost effectiveness and appropriate use of computer-navigated RSA warrant specific investigation in future studies.

LEVEL OF EVIDENCE

II, prospective cohort study.

TRIAL REGISTRATION

9/1/2020 to 12/31/2021.

Suprascapular nerve injury after reverse total shoulder arthroplasty: correlation with screw out of vault penetration and functional situation: prospective study

BACKGROUND

Baseplate screws have been suggested as a possible cause of suprascapular neuropathy after reverse total shoulder arthroplasty. This study aims to investigate the association between screw penetration out of the vault, electromyographic study, and the clinical outcomes.

METHODS

A total of 31 patients who underwent reverse total shoulder arthroplasty for cuff tear arthropathy were prospectively enrolled. They were followed up for a minimum of 24 months. All patients underwent computed tomography 6 months postoperatively to determine the extraosseous position of the screws (perforation of the second bone cortex and protrusion into the supra- or infraspinatus fossa). Electrodiagnostic evaluation was performed preoperatively and postoperatively to stablish any relation between cortex perforation of the screw and suprascapular nerve (SSN) injury. Clinical outcomes pre- and postoperatively (Constant score, ranges of motion, and visual analog scale) of patients with and without documented injury were recorded.

RESULTS

A total of 14 patients (45.2%) had an abnormal preoperative SSN electrodiagnostic study (chronic or disuse injuries), and 6 patients (19.4%) had an abnormal postoperative study (acute injury). Of the 6 patients, 2 cases appeared over the pre-existing lesion and 4 appeared over an intact preoperative nerve, all of them affecting the infraspinatus branch of the SSN. Perforation of the second cortex was detected for 60% of superior screws and 40% of posterior screws. The mean lengths of the superior and posterior screws were 30 and 18.2 mm, respectively. Patients with screw perforation of the second cortex were assessed as having a high risk of nerve injury (40% vs. 9.5%).

CONCLUSIONS

Preoperative SSN injuries do not have a significant clinical impact and do not predispose to an acute postoperative SSN lesion. The Constant score and visual analog scale score for patients with acute SSN injuries were not statistically different from those without SSN injury. The extraosseous position of the screw increases the probability of an SSN injury to 31%. This risk is higher with the posterior screw, which leads us to question whether it is really necessary to use it.

Reverse shoulder arthroplasty: State-of-the-art

The reverse shoulder arthroplasty conceived by Paul Grammont in 1985 has gradually gained popularity as a treatment for multiple shoulder diseases. Unlike previous reverse shoulder prosthesis characterized by unsatisfactory results and a high glenoid implant failure rate, the Grammont design has immediately shown good clinical outcomes. This semi constrained prosthesis solved the issues of the very first designs by medializing and distalizing the center of rotation with an increased stability of the replacement of the component. The indication was initially limited to cuff tear arthropathy (CTA). It has then been expanded to irreparable massive cuff tears and displaced humeral head fractures. The most frequent problems of this design are a limited postoperative external rotation and scapular notching. Different modifications to the original Grammont design have been proposed with the aim of decreasing the risk of failure and complications and improving the clinical outcomes. Both the position and version/inclination of the glenosphere and the humeral configuration (e.g. neck shaft angle) influence the RSA outcomes. A lateralized glenoid (whether with bone or metal) and a 135° Inlay system configuration leads to a moment arm which is the closest to the native shoulder. Clinical research will focus on implant designs reducing bone adaptations and revision rate, strategies to prevent more effectively infections. Furthermore, there is still room for improvement in terms of better postoperative internal and external rotations and clinical outcomes after RSA implanted for humeral fracture and revision shoulder arthroplasty.

Surgeon-designed patient-specific instrumentation improves glenoid component screw placement for reverse total shoulder arthroplasty in a population with small glenoid dimensions

PURPOSE

Glenoid component loosening is a potential complication of reverse total shoulder arthroplasty (rTSA), occurring in part due to lack of adequate screw purchase in quality scapular bone stock. This study was to determine the efficacy of a surgeon-designed, 3D-printed patient-specific instrumentation (PSI) compared to conventional instrumentation (CI) in achieving longer superior and inferior screw lengths for glenoid component fixation.

METHODS

A multi-centre retrospective analysis of patients who underwent rTSA between 2015 and 2020. Lengths of the superior and inferior locking screws inserted for fixation of the glenoid baseplate component were recorded and compared according to whether patients received PSI or CI. Secondary outcomes included operative duration and incidence of complications requiring revision surgery.

RESULTS

Seventy-three patients (31 PSI vs. 42 CI) were analysed. Average glenoid diameter was 24.5 mm (SD: 3.1) and 81% of patients had smaller glenoid dimensions compared to the baseplate itself. PSI produced significantly longer superior (44.7 vs. 30.7 mm; P < 0.001) and inferior (43.0 vs. 31 mm; P < 0.001) mean screw lengths, as compared to CI. A greater proportion of maximal screw lengths for the given rTSA construct (48 mm) were observed in the PSI group (71.9% vs. 11.9% superior, 59.4% vs. 11.9% inferior). Operative duration was not statistically significantly different between the PSI and CI groups (150 min vs. 169 min, respectively; P = 0.229). No patients had radiographic loosening of the glenoid component with an average of 2-year follow-up.

CONCLUSION

PSI facilitates longer superior and inferior screw placement in the fixation of the glenoid component for rTSA. With sufficient training, PSI can be designed and implemented by surgeons themselves.

Does fluoroscopy improve baseplate position compared to conventional technique in reverse shoulder arthroplasty? A preliminary study

Background

Accurate placement of glenoid component in reverse shoulder arthroplasty remains a challenge for surgeons of all levels of expertise; however, no studies have evaluated the utility of fluoroscopy as a surgical assistance method.

Methods

Prospective comparative study of 33 patients undergoing primary reverse shoulder arthroplasty during a 12-month period. Fifteen patients had a baseplate placed using the conventional "free hand" technique (control group), and 18 patients using intraoperative fluoroscopy assistance group, in a case-control design. Postoperative glenoid position was evaluated on postoperative Computed Tomography (CT) scan.

Results

The mean deviation of version and inclination for fluoroscopy assistance vs. control group was 1.75° (0.675-3.125) vs. 4.2° (1.975-10.45) (p = .015), and 3.85° (0-7.225) vs. 10.35° (4.35-18.75) (p = .009). The distance from the central peg midpoint to the inferior glenoid rim (fluoroscopy assistance 14.61 mm/control 4.75 mm, p = .581) and the surgical time (fluoroscopy assistance 1.93 ± 0.57/control 2.18 ± 0.44 h, p = .400) showed no differences, with an average radiation dose of 0.45 mGy and fluoroscopy time of 14 s.

Conclusions

Accurate axial and coronal scapular plane positioning of glenoid component is improved with intraoperative fluoroscopy at the cost of a greater radiation dose and without differences in surgical time. Comparative studies are needed to determine whether their use in relation to more expensive surgical assistance systems result in similar effectiveness.L evel of evidence : Level III, therapeutic study.

Does computer-assisted navigation improve baseplate screw configuration in reverse shoulder arthroplasty? A systematic review and meta-analysis of comparative studies

Introduction

Navigation technologies have improved accuracy and precision in positioning glenoid components during shoulder arthroplasty. The influence of navigation on baseplate screw placement has not been independently investigated. This study aimed to evaluate and synthesize the best scientific evidence on the influence of intraoperative navigation on the length and number of screws for primary baseplate fixation in reverse total shoulder arthroplasty procedures.

Methods

In August 2022, PubMed, Scopus, and Embase databases were accessed. We analyzed the screw purchase length, the number of screws required for the fixation of the baseplate, and the proportion of cases fixed with two screws in all clinical trials, comparing navigation to standard instrumentation for reverse shoulder arthroplasty. Following an evaluation of the heterogeneity of the studies, DerSimonian-Laird random-effects models were utilized to merge data from separate studies.

Results

The systematic search revealed a total of 2034 articles. After excluding duplicates and irrelevant studies, 633 shoulder arthroplasties from 6 trials were included in the analysis. The pooled mean difference in screw purchase length was 5.839 mm (95 %CI 4.496 to 7. 182) in favor of navigation (P < .001). In addition, significant differences were also found in the number of screws per case (- 0.547, 95 %CI -0.890 to -0.203, P = .002) and in the proportion of cases fixed with two screws (Odds Ratio 3.182 95 %CI 1.057 to 9.579, P = .040) in favor of the navigation group.

Conclusions

Intraoperative navigation improves the baseplate screw placement, allowing for a greater screw purchase length and fewer screws to achieve primary fixation of the glenoid component during reverse shoulder arthroplasty. It is unclear whether these improvements will increase the longevity of the prosthesis or the clinical outcomes of the patients.

Accuracy of an Apparatus for Measuring Glenoid Baseplate Micromotion in Reverse Shoulder Arthroplasty

Reverse shoulder arthroplasty (RSA) is used to treat patients with cuff tear arthropathy. Loosening remains one of the principal modes of implant failure and the main complication leading to revision. Excess micromotion contributes to glenoid loosening. This study assessed the predictive accuracy of an experimental system designed to assess factors contributing to RSA glenoid baseplate micromotion. A half-fractional factorial experiment was designed to assess 4 factors: central element type (screw vs. peg), central element length (13.5 vs. 23.5 mm), anterior posterior peripheral screw type (locking vs. nonlocking) and cancellous bone density (10 vs. 25 pounds per cubic foot [pcf]). Four linear variable differential transducers (LVDTs) recorded micromotion from a stainless-steel disc surrounding a modified glenosphere. The displacements were used to interpolate micromotion at each of the respective peripheral screw positions. The mean absolute percentage error (MAPE) was used to determine the predictive accuracy and error range of the system. The MAPE for each condition ranged from 6.8% to 12.9% for an overall MAPE of (9.5&amp;#177;0.9)%. The system had an error range of 2.7 &amp;#181;m to 20.1 &amp;#181;m, which was lower than those reported by prior studies using optical systems. One of the eight conditions had micromotion that exceeded 150 &amp;#181;m. These findings support the use of displacement transducers, specifically LVDTs, as an accurate system for determining RSA baseplate micromotion in rigid polyurethane foam bone surrogates.

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.

Patient-specific instrumentation improves the reproducibility of preoperative planning for the positioning of baseplate components with reverse total shoulder arthroplasty: a comparative clinical study in 39 patients

BACKGROUND

The application of patient-specific instrumentation (PSI) for reverse total shoulder replacement has been rapidly increasing, which could reduce errors in implant positioning. Although PSI theoretically holds promise, evidence of the accuracy and reliability of PSI in shoulder replacement surgery is limited.

METHODS

Thirty-nine shoulders that underwent reverse total shoulder arthroplasty were included in this study and categorized into two groups: the conventional (n = 20) and PSI (n = 19) groups. Screw (length and angle) and baseplate (version, inclination, translation, and rotation) positioning were calculated based on postoperative computed tomography images using a three-dimensional measurement tool. The difference between the values of the preoperative target and postoperative measurement was calculated to evaluate the reproducibility of preoperative planning. Screw involvement in the suprascapular and spinoglenoid notches was assessed. Thus, the correlation between the position of the baseplate and the screws was assessed.

RESULTS

The mean differences between the planned length and angle (anteroposterior and superoinferior angles) and postoperative measurement in the PSI group were significantly smaller than those in the conventional group. Similarly, the mean difference in baseplate rotation between the planned and postoperative measurements in the PSI group was significantly lower than that in the conventional group (4.5° vs 10.6°; P < .001). The spinoglenoid notch was involved in 10 cases in the conventional group and 2 cases in the PSI group, and this difference was significant (P = .014). Overall, the mean difference between the preoperative and postoperative version, inferior inclination, and rotation values for the baseplate position was significantly correlated with the values for screw position (length and angle).

CONCLUSIONS

PSI improves the reproducibility of preoperative planning for baseplate and screw positioning and reduces the risk of neurovascular injury in reverse total shoulder arthroplasty.

Effect of Implant Size, Version and Rotator Cuff Tendon Preservation on the Outcome of Reverse Shoulder Arthroplasty

Introduction: Functional outcomes following reverse geometry shoulder arthroplasty can vary. This study assessed the effects of glenosphere size, humeral stem version, posterior rotator cuff status and subscapularis repair on patient-reported outcome and range of motion. 

Methods: A consecutive series of 132 patients from two orthopaedic centres that use the same onlay system for reverse shoulder arthroplasty were reviewed over a six-year period. Outcome measures consisted of the Oxford Shoulder score (OSS) and range of motion (ROM) at one year following surgery. These were assessed against glenosphere sizes (small (36-38 mm) and large (40-42 mm)), humeral stem retroversion (less or more than 20 degrees), rotator cuff status (posterior rotator cuff present or absent) and subscapularis tendon (repaired or not) at the end of procedure.

Results: Larger glenospheres and less humeral stem retroversion yielded better ROM and OSS but this was not statistically significant. Subscapularis repair had no effect on outcomes. Preservation of posterior rotator cuff tendons improved functional outcomes. The number of tendons present at the end of procedure had a positive effect on outcome (best with two tendons and better with one compared to a completely bald humeral head).

Conclusion: Preservation of posterior rotator cuff tendons during reverse shoulder arthroplasty improves clinical outcomes unlike subscapularis repair which was found to be unnecessary. Implant size and version in reverse geometry arthroplasty have no significant effects on clinical outcome.

Identifying areas of screw fixation in glenoids with severe bone loss in shoulder arthroplasty

BACKGROUND

Severe glenoid bone loss (SGBL) poses significant technical challenges. Adequate fixation of glenoid implants may require the use of alternative screw placement. Although bone volumes for the spine and lateral pillars have previously been defined, insufficient evidence exists regarding the distribution of screw placement for fixation in such regions for cases with SGBL. The purpose of this study is to evaluate the variability of screw placement. We hypothesize that determining this variability and establishing common patterns of glenoid bone loss will allow for recommendations for preoperative planning, and implant design and selection.

METHODS

An internal registry of 2 high-volume shoulder and elbow surgeons was queried, and 65 three-dimensional scapulae models exhibiting SGBL were identified. A fellowship-trained shoulder and elbow surgeon simulated the placement of two 3.5 mm × 30 mm screws, one in the scapular spine (CS) bone volume and one in the inferior column (IS) bone volume. Three orthogonal reference planes were created using anatomic reference points: the scapula trigonum, estimated glenoid center, and inferior pole. Screw positions were mapped, and deviations from the reference planes were calculated. Mutual positions of the IS to CS were also computed. Intraobserver reliability was assessed using 10 randomly selected samples. Median and 25th and 75th percentiles were reported for screw orientation distributions. Means and standard deviations were reported for screw head positions.

RESULTS

We demonstrated excellent intraobserver reliability (intraclass correlation coefficients, 0.90-0.98). Fifty percent of CS were oriented 10° ± 5° of retroversion from the scapula plane, with 5° ± 5° of inclination. For IS, 50% were positioned 0° ± 4° from the scapula plane, with -33° ± 7° of inclination. The relationship of the IS with the CS was medial and posterior in 49% of cases, lateral and posterior in 45%, and lateral and anterior in 6% of cases. On average, the distance between the CS and IS heads was 25 mm ± 4 mm.

DISCUSSION

For SGBL, adequate fixation of glenoid implants can be achieved by placing screws in the spine and lateral columns, with excellent reproducibility. Future implant designs should accommodate CS positioned -16° to -5° from the scapula plane, with 0° to 12° of inclination, and IS positioned -6° to 4° from the scapula plane, with -40° to -25° of inclination. Moreover, mutual screw positions suggested bone loss distributions anteriorly and inferiorly. Future implant designs should consider the potential benefits of augmentation to accommodate interscrew distances of 21-29 mm and anatomic locations of the IS relative to the CS.

The Evolution of Reverse Total Shoulder Arthroplasty-From the First Steps to Novel Implant Designs and Surgical Techniques

Purpose of Review: The purpose of this review is to summarize recent literature regarding the latest design modifications and biomechanical evolutions of reverse total shoulder arthroplasty and their impact on postoperative outcomes. Recent findings: Over the past decade, worldwide implantation rates of reverse total shoulder arthroplasty have drastically increased for various shoulder pathologies. While Paul Grammont’s design principles first published in 1985 for reverse total shoulder arthroplasty remained unchanged, several adjustments were made to address postoperative clinical and biomechanical challenges such as implant glenoid loosening, scapular notching, or limited range of motion in order to maximize functional outcomes and increase the longevity of reverse total shoulder arthroplasty. However, the adequate and stable fixation of prosthetic components can be challenging, especially in massive osteoarthritis with concomitant bone loss. To overcome such issues, surgical navigation and patient-specific instruments may be a viable tool to improve accurate prosthetic component positioning. Nevertheless, larger clinical series on the accuracy and possible complications of this novel technique are still missing.

Factors Influencing Acromial and Scapular Spine Strain after Reverse Total Shoulder Arthroplasty: A Systematic Review of Biomechanical Studies

BACKGROUND

Acromial and scapular spine fractures after reverse total shoulder arthroplasty (RTSA) can be devastating complications leading to substantial functional impairments. The purpose of this study was to review factors associated with increased acromial and scapular spine strain after RTSA from a biomechanical standpoint.

METHODS

A systematic review of the literature was conducted based on PRISMA guidelines. PubMed, Embase, OVID Medline, and CENTRAL databases were searched and strict inclusion and exclusion criteria were applied. Each article was assessed using the modified Downs and Black checklist to appraise the quality of included studies. Study selection, extraction of data, and assessment of methodological quality were carried out independently by two of the authors. Only biomechanical studies were considered.

RESULTS

Six biomechanical studies evaluated factors associated with increased acromial and scapular spine strain and stress. Significant increases in acromial and scapular spine strain were found with increasing lateralization of the glenosphere in four of the included studies. In two studies, glenosphere inferiorization consistently reduced acromial strain. The results concerning humeral lateralization were variable between four studies. Humeral component neck-shaft angle had no significant effect on acromial strain as analysed in one study. One study showed that scapular spine strain was significantly increased with a more posteriorly oriented acromion (55° vs. 43°; p < 0.001). Another study showed that the transection of the coracoacromial ligament increased scapular spine strain in all abduction angles (p < 0.05).

CONCLUSIONS

Glenoid lateralization was consistently associated with increased acromial and scapular spine strain, whereas inferiorization of the glenosphere reduced strain in the biomechanical studies analysed in this systematic review. Humeral-sided lateralization may increase or decrease acromial or scapular spine strain. Independent of different design parameters, the transection of the coracoacromial ligament resulted in significantly increased strains and scapular spine strains were also increased when the acromion was more posteriorly oriented. The results found in this systematic review of biomechanical in-silico and in-vitro studies may help in the surgical planning of RTSA to mitigate complications associated with acromion and scapular spine fracture.

Trabecular bone density distribution in the scapula of patients undergoing reverse shoulder arthroplasty

Background

To improve implant survival after reverse shoulder arthroplasty (RSA), surgeons need to maximize screw fixation. However, bone density variation and distribution within the scapula are not well understood as they relate to RSA. The three columns of bone in the scapula surrounding the glenoid fossa are the lateral border, the base of the coracoid process, and the spine of the scapula. In our previous study by Daalder et al on cadaveric specimens, the coracoid column was significantly less dense than the lateral border and spine. This study’s objective was to verify whether these results are consistent with computer tomography (CT) scan information from patients undergoing RSA.

Methods

Two-dimensional axial CT images from twelve patients were segmented, and a three-dimensional digital model of the scapula was subsequently created using Mimics 17.0 Materialise Software (Leuven, Belgium). Hounsfield unit (HU) values representing cortical bone were filtered out to determine the distributions of trabecular bone density. An analysis of variance with post hoc Bonferroni tests determined the differences in bone density between the columns of bone in the scapula.

Results

The coracoid superolateral (270 ± 45.6 HU) to the suprascapular notch was significantly less dense than the inferior (356 ± 63.6 HU, P = .03, d_s = 1.54) and anterosuperior portion of the lateral border (353 ± 68.9 HU, P = .04, d_s = 1.42) and the posterior (368 ± 70 HU, P = .007, d_s = 1.65) and anterior spine (370 ± 78.9 HU, P = .006, d_s = 1.54).

Discussion/Conclusion

The higher-density bone in the spine and lateral border compared with the coracoid region may provide better bone purchase for screws when fixing the glenoid baseplate in RSA. This is in agreement with our previous study and indicates that the previous cadaveric results are applicable to clinical CT scan data. When these studies are taken together, they provide robust evidence for clinical applications, including having surgeons aim screws for higher-density regions to increase screw fixation, which may decrease micromotion and improve implant longevity.

Glenoid baseplate screw fixation in reverse shoulder arthroplasty: does locking screw position and orientation matter?

BACKGROUND

The longevity of a reverse total shoulder arthroplasty prosthesis can be compromised by glenoid baseplate loosening. Circular baseplate designs can be secured with superoinferior (SI) locking screws and anteroposterior (AP) compression screws or vice versa (AP-locking and SI-compression screws). This biomechanical cadaveric study investigated screw position (locking screws SI vs. AP and compression screws AP and SI) and screw orientation (parallel vs. divergent) to determine quantitative differences in baseplate micromotion.

METHODS

Ten paired fresh-frozen cadaveric scapulae (n = 20) were implanted with a standard circular baseplate (∅ = 29 mm). The specimens were randomized into SI-locking or AP-locking screw configurations with the screw orientation directed either parallel or angled divergently at 15°. This yielded a total of 4 groups for statistical comparison: SI-locking_parallel, SI-locking_divergent, AP-locking_parallel, and AP-locking_divergent, which were subjected to axial eccentric loading on the implanted baseplates, similar to the American Standard of Testing of Materials standard for shoulder joint arthroplasty.

RESULTS

In both static and cyclic testing, there were no statistically significant differences (P = .6) in micromotion between SI-locking (2.9 ± 0.8 μm) and AP-locking (3.5 ± 1.5 μm) configurations. In addition, there were no statistically significant differences (P = .2) in the divergent screw orientation group (2.0 ± 0.7 μm) vs. the parallel group (4.0 ± 1.5 μm).

CONCLUSION

All configurations of screw position and screw orientation tested in a circular reverse baseplate have similar time-zero fixation in an intact glenoid bone model. In addition, the resultant micromotions for all configurations tested fell far below the 150 μm threshold for bone ongrowth.

Short stem humeral components in reverse shoulder arthroplasty: stem alignment influences the neck-shaft angle

INTRODUCTION

Shorter humeral reverse total shoulder arthroplasty (RTSA) stems may reduce stress shielding, however, potentially carry the risk of varus/valgus malalignment. This radiographic study's purpose was to measure the incidence of stem malalignment and thus the realized neck-shaft angle (NSA). The hypothesis was that malalignment of the stem is a frequent postoperative radiographic finding.

METHODS

Radiographs of an uncemented curved short stem RTSA with a 145° NSA were reviewed. The study group included 124 cases at a mean age of 74 (range 48-91) years. The humeral stem axis was measured and defined as neutral if the value fell within ± 5° of the longitudinal humeral axis. Angular values > 5° were defined as malaligned in valgus or varus. The filling ratio of the implant within the humeral shaft was measured at the level of the metaphysis (FR_met) and diaphysis (FR_dia).

RESULTS

The average humeral stem axis angle was 4 ± 3° valgus, corresponding to a true mean NSA of 149 ± 3°. Stem axis was neutral in 73% (n = 90) of implants. Of the 34 malaligned implants, 82% (n = 28) were in valgus (NSA = 153 ± 2°) and 18% (n = 6) in varus (NSA = 139 ± 1°). The average FR_met and FR_dia were 0.68 ± 0.11 and 0.72 ± 0.11, respectively. A low positive association was found between stem diameter and filling ratios (r = 0.39; p < 0.001); indicating smaller stem sizes were more likely to be misaligned.

CONCLUSION

Uncemented short stem implants may decrease stress shielding; however, approximately one quarter were implanted > 5° malaligned. The majority of malaligned components (86%) were implanted in valgus, corresponding to an NSA of > 150°. As such, surgeons must be aware that shorter and smaller stems may lead to axial malalignment influencing the true SA.

LEVEL OF EVIDENCE

Level IV, retrospective study.

Pre-Operative CT-Based Planning Integrated With Intra-Operative Navigation in Reverse Shoulder Arthroplasty: Data Acquisition and Analysis Protocol, and Preliminary Results of Navigated Versus Conventional Surgery

Reverse total shoulder arthroplasty (RSA) successfully restores shoulder function in different conditions. Glenoid baseplate fixation and positioning seem to be the most important factors influencing RSA survival. When scapular anatomy is distorted (eccentric osteoarthrirtis, rotator cuff arthropathy), optimal baseplate positioning and secure screw purchase can be challenging. The aim of this study was to evaluate whether CT-based pre-operative planning, integrated with intra-operative navigation could improve glenoid baseplate fixation and positioning by increasing screw length, reducing number of screws required to obtain fixation and increasing the use of augmented baseplate to gain the desired positioning. Twenty patients who underwent navigated RSA were compared retrospectively with 20 patients operated on with a conventional technique. All the procedures were performed by the same surgeon, using the same implant. Mean screw length was significantly longer in the navigation group (35.5 ± 4.4 mm vs 29.9 ± 3.6 mm; p = .001). Significant higher rate of optimal fixation using 2 screws only (17 vs 3 cases, p = .019) and higher rate of augmented baseplate usage (13 vs 4 cases, p = .009) was also present in the navigation group. Pre-operative CT-based planning integrated with intra-operative navigation can improve glenoid component positioning and fixation, possibly leading to an improvement of RSA survival.

Intraoperative navigation and preoperative templating software are associated with increased glenoid baseplate screw length and use of augmented baseplates in reverse total shoulder arthroplasty

Background

Preoperative templating software and intraoperative navigation have the potential to impact baseplate augmentation utilization and increase screw length for baseplate fixation in reverse total shoulder arthroplasty (rTSA). We aimed to assess their impact on the (1) baseplate screw length, (2) number of screws used, and (3) frequency of augmented baseplate use in navigated rTSA.

Methods

We compared 51 patients who underwent navigated rTSA with 63 controls who underwent conventional rTSA at a single institution. Primary outcomes included the screw length, composite screw length, number of screws used, percentage of patients in whom 2 screws in total were used, and use of augmented baseplates.

Results

Navigation resulted in the use of significantly longer individual screws (36.7 mm vs. 30 mm, P < .0001), greater composite screw length (84 mm vs. 76 mm, P = .048), and fewer screws (2.5 ± 0.7 vs. 2.8 ± 1, P = .047), as well as an increased frequency of using 2 screws in total (35 of 51 patients [68.6%] vs. 32 of 63 controls [50.8%], P = .047). Preoperative templating resulted in more frequent augmented baseplate utilization (76.5% vs. 19.1%, P < .0001).

Conclusion

The difference in the screw length, number of screws used, and augmented baseplate use demonstrates the evolving role that computer navigation and preoperative templating play in surgical planning and the intraoperative technique for rTSA.

Distal clavicle autograft augmentation for glenoid bone loss in revision shoulder arthroplasty: results and technique

BACKGROUND

Structural bone graft for reconstruction of glenoid bone stock is often necessary in the setting of revision shoulder arthroplasty. This study introduces a new structural autograft technique using the distal clavicle for treatment of glenoid bone loss in the setting of revision shoulder arthroplasty.

METHODS

This is a retrospective, single-surgeon study of patients with significant glenoid bone loss requiring revision shoulder arthroplasty with autologous distal clavicle bone grafting to the glenoid. Twenty patients with failed shoulder arthroplasty who underwent revisions of their glenoid components between 2015 and 2019 were retrospectively identified. Sixteen patients were available with follow-up of greater than 1 year. Patient records and radiographs were reviewed for intraoperative and postoperative complications. Preoperative and postoperative function were evaluated by physical examination and patient-reported outcome surveys.

RESULTS

There were no observed intraoperative complications relating to the distal clavicle autograft harvest or placement. There were no iatrogenic nerve injuries or intraoperative instability. One of the 16 patients developed postoperative loosening and subsequent failure of the glenoid baseplate, requiring revision. One additional patient demonstrated increased elevation of the coracoclavicular interval postoperatively, likely related to the distal clavicle autograft harvest. At a mean follow-up of 25 months, 15 of 16 glenoid implants remained well fixed (93.4%), with no evidence of infection, or impingement demonstrated radiographically or clinically. Average patient age was 69 years at the time of surgery. Forward elevation improved from 76° to 123° at final follow-up (P = .0002). The American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score improved from an average of 35.8 to 67.8 at mean follow-up (P = .001). The visual analog scale score improved from an average of 5.9 to 2 at mean follow-up, though not statistically significant (P = .068). There was no significant change in external rotation following surgery (P = .319).

CONCLUSION

Osteolysis and bone loss of the glenoid poses a challenging problem in revision shoulder arthroplasty. Distal clavicle autograft augmentation is a viable and reproducible technique to manage structural glenoid defects.

Influence of reverse total shoulder arthroplasty baseplate design on torque and compression relationship

Background

A linear relationship between baseplate insertion torque and compression force in reverse shoulder arthroplasty (RSA) baseplates with central screw design has been recently established. In this study, we evaluated 3 different baseplate designs and their influence on the torque-compression relationship.

Methods

Three different RSA baseplate designs were evaluated through biomechanical testing using a glenoid vault, bone surrogate model. A digital torque gauge was used to measure insertion torque applied to the baseplate, whereas compression data were collected continuously from a load cell. Additionally, 2 predictive models were developed to predict the compression forces of each baseplate design at varying levels of torque.

Results

A linear relationship was found between baseplate compression and insertion torque for all 3 baseplate designs. Both the monoblock and 2-piece locking designs achieved the goal torque of 6.8 Nm, whereas the 2-piece nonlocking design did not due to material strip-out. No significant difference in maximum compression was found between the monoblock and 2-piece locking designs. However, the 2-piece nonlocking design achieved significantly higher compression. Both predictive models were shown to adequately predict compressive forces at different torque inputs for the monoblock and 2-piece locking designs but not the 2-piece nonlocking design.

Conclusion

The torque-compression relationship of a central screw baseplate is significantly affected by baseplate design. A 2-piece nonlocking baseplate reaches higher compression levels and risks material strip-out at lower insertional torques compared with a monoblock and 2-piece locking design. This has implications both on component design and on surgeon tactile feedback during surgery.

Relationship Between Insertion Torque and Compression Strength in the Reverse Total Shoulder Arthroplasty Baseplate

Reverse shoulder arthroplasty is a well-established procedure, however, there is limited data in the literature regarding adequate insertion torque and the resulting compression for glenoid baseplate fixation. In this biomechanical study, we evaluated the relationship between insertion torque and baseplate compression by simultaneously measuring the insertion torque and axial compressive forces generated by two reverse shoulder arthroplasty baseplates with central screw design. Three different bone surrogates were chosen to mimic clinical scenarios where differences in compression achieved during baseplate insertion may exist due to varying bone quality. Epoxy resin sheets were combined with the bone surrogates to simulate the glenoid vault. A digital torque gauge was used to measure insertion torque applied to the baseplate, while compression data were collected continuously from a load cell. A strong positive correlation was found between baseplate compression and insertion torque. Among the lower density bone surrogates, neither baseplate design reached maximum insertion torque (6.8 Nm) due to material strip-out. This phenomenon did not occur in denser bone surrogates. Both baseplate designs experienced a significant increase in mean baseplate compression as insertion torque increased and were found to behave similar in the denser bone surrogates. The results presented here suggest that larger compressive forces can be achieved with an increase in insertion torque in denser bone surrogates, but caution must be used when trying to achieve fixation in poor-quality bone. Clinically, this could be useful preoperatively to minimize baseplate failure, and in further studies regarding baseplate design for improved initial fixation and stability. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:871-879, 2020.

Impact of screw length and screw quantity on reverse total shoulder arthroplasty glenoid fixation for 2 different sizes of glenoid baseplates

Background

Little guidance exists regarding the minimum screw length and screw quantity necessary to achieve fixation in reverse total shoulder arthroplasty (rTSA); to that end, this study quantified the displacement of 2 different sizes of glenoid baseplates using multiple different screw lengths and quantities of screws in a low-density polyurethane bone-substitute model.

Methods

Testing of rTSA glenoid loosening was conducted according to ASTM F 2028-17. To independently evaluate the impact of screw quantity and screw length on rTSA glenoid fixation for 2 different sizes of glenoid baseplates, baseplates were constructed using 2 screws, 4 screws, or 6 screws (with the latter being used for the larger baseplate only) with 3 different poly-axial locking compression screw lengths.

Results

Both sizes of glenoid baseplates remained well fixed after cyclic loading regardless of screw length or screw quantity. Baseplates with 2 screws had significantly greater displacement than baseplates with 4 or 6 screws. No differences were observed between baseplates with 4 screws and those with 6 screws (used for the larger baseplate). Both sizes of baseplates with 18-mm screws had significantly greater displacement than baseplates with 30- or 46-mm screws. For larger baseplates, those with 30-mm screws had significantly greater displacement than those with 46-mm screws in the superior-inferior direction.

Discussion

For the 2 different sizes of baseplates tested in this study, rTSA glenoid fixation was impacted by both screw quantity and screw length. Irrespective of screw quantity, longer screws showed significantly better fixation. Irrespective of screw length, the use of more screws showed significantly better fixation, up to a point, as the use of more than 4 screws showed no incremental benefit. Finally, longer screws can be used as a substitute for additional fixation if it is not feasible to use more screws.

Is the version angle of the glenoid different in bone and cartilage? An MRI study

Background/aim

To determine whether or not there is a difference between the version of the bone and cartilage surfaces of the glenoid. Axial magnetic resonance imaging (MRI) slices were examined in order to evaluate the measurements taken based on both the cartilage and bone joint surfaces.

Materials and methods

A retrospective evaluation was made of the MRI scans of 182 patients. All of the reviewers independently measured the glenoid version angles of all of the patients from 1–182. The process was then repeated, with each reviewer taking second measurements of the angles from 1–182. Pearson correlation coefficient analysis was applied to evaluate the interaction and relationships between the measurements taken from the bone and cartilage. The intra- and interobserver interclass correlation coefficients (ICCs) were assessed. Analysis of variance was applied to determine any interobserver significant differences.

Results

The mean glenoid version was determined as –3.58 ± 4.08° in the bone-based measurements and –5.81 ± 4.30° in the cartilage-based measurements. The cartilage- and bone-based measurements were found to have inter- and intraobserver reliability. A statistically significant difference was observed between the mean cartilage-based version and the mean bone-based version. Changes in the cartilage- and bone-based measurements were correlated; however, this change was not linear.

Conclusion

The cartilage-based version showed a significant difference from the bone- based version. Therefore, in the preoperative planning and evaluation of glenoid-based pathologies, it would be more appropriate to evaluate both the bone and cartilage surface on MRI.

Role of intraoperative navigation in the fixation of the glenoid component in reverse total shoulder arthroplasty: a clinical case-control study

BACKGROUND

Fixation of the glenoid baseplate in reverse total shoulder arthroplasty (rTSA) is an important factor in the success of the procedure. There is limited information available regarding the effect of navigation on fixation characteristics. Therefore, the aims of this study were to determine whether computed tomography-based computer navigation improved the glenoid base plate fixation by (1) increasing the length of screw purchase, (2) altering screw angulation, and (3) decreasing central cage perforation in patients undergoing rTSA.

METHODS

Patients undergoing rTSAs using navigation (NAV, N = 27) and manual technique (MAN, N = 23) from January 2014 to July 2017 were analyzed in a case-control design. Screw purchase length and central cage perforation were assessed using multiplanar computed tomography.

RESULTS

Median screw purchase length was significantly longer in the NAV group for both anterior (20 mm vs. 15 mm, P < .01) and posterior screws (20 mm vs. 13 mm, P < .01). In addition, the NAV group displayed significantly lower incidences of inadequate screw purchase (<22 mm) for the anterior (64.7% vs. 95.2%, P = .03) and posterior (70.6% vs. 100%, P = .01) screws. Significant differences in axial and coronal screw angulation were observed between groups. Similarly, the NAV group displayed significantly reduced incidence of central cage perforation (17.7% vs. 52.4%, P = .04).

CONCLUSION

The use of computer-assisted navigated rTSA contributes to significant alterations in screw purchase length, screw angulation, and central cage perforation of the glenoid baseplate compared with non-navigated methods.

Factors contributing to glenoid baseplate micromotion in reverse shoulder arthroplasty: a biomechanical study

BACKGROUND

Reverse shoulder arthroplasty (RSA) is typically performed in patients with cuff tear arthropathy. A common type of RSA baseplate has a central peg and 4 peripheral screws inserting into the glenoid surface. Baseplate failure is a significant postoperative complication that reduces prosthetic longevity and usually requires revision surgery. This study evaluated the contribution of mechanical factors on initial baseplate fixation.

MATERIALS AND METHODS

This study simulated glenoid baseplate loading in a RSA. A half-fractional factorial design was used to test 5 factors: bone density (160 or 400 kg/m³), screw length (18 or 36 mm), number of screws (2 or 4), screw angle (neutral or diverging), and central peg length (13.5 or 23.5 mm). Trials were cyclically loaded at a 60° angle with 500 N for 1000 cycles. Micromotion at 4 peripheral screw positions was analyzed using a multifactorial analysis of variance (P < .05).

RESULTS

We found an increase in micromotion with 3 scenarios: (1) lower bone density at all screw positions; (2) shorter central peg length at the inferior, superior and anterior screws; and (3) shorter screw length at the inferior and anterior screws. There were interactions between bone density and screw length at the inferior and anterior screws and between bone density and central peg length at the inferior, superior, and anterior screws.

DISCUSSION

Greater bone density, a longer central peg, and longer screws provide improved initial glenoid fixation in an RSA, whereas the number of screws, and the angle of screw insertion do not. These findings may help minimize baseplate failure and revision operations.

Cement augmentation of glenoid baseplate screws does not improve primary stability in reversed shoulder arthroplasty: A cadaveric study

INTRODUCTION

Cuff tear arthritis and complex proximal humeral fractures are common pathologies that are frequently addressed by the implantation of a reversed shoulder prosthesis. The present cadaveric study aimed to analyze the effect of cement augmentation of the glenoid component on the primary stability in geriatric patients.

HYPOTHESIS

Cement augmentation of glenoid baseplate screws has an influence on primary stability in reversed shoulder arthroplasty (RSA).

MATERIALS AND METHODS

Glenoid base plates (Delta Xtend, DePuy Synthes, Westchester, USA) were implanted in 6 pairs of formalin-fixated scapulae of 4 female and 2 male donors (average age 83 years). Two angle stable screws were placed at the superior and inferior position. Cement augmentation was performed with 2ml bone cement (Kyphon, Medtronic, Minneapolis, USA) per screw in right specimens. Afterwards, biomechanical testing with 600 to 1000N (100 cycles) at a 65° abduction angle was performed. Finally, a load-to-failure analysis was conducted.

RESULTS

No implant loosening was observed during cyclic tests from 600N to 1000N. In addition no difference in the plastic deformation was detected at 600N (p=0.301), 700N (p=0.522), 800N (p=0.480), 900N (p=0.521) and 1000N (p=0.748). Load-to-failure analyses revealed implant loosening at 3314N (SD 823N) in the cement-augmented implants and at 3059N (SD 974N) in scapulae with non-cemented screws (p=0.522).

DISCUSSION

Cement-augmented fixation of the glenoid component did not result in an increased primary stability in this study. Thus, the application of cement should be critically assessed considering associated risks and increased costs.

LEVEL OF PROOF

Basic science study, controlled laboratory study.

Another Glenoid Measurements for Shoulder Surgery

Background

We analyzed the angle between the glenoid anterior surface and glenoid axis, the range of the glenoid apex and the location of the glenoid apex for assistance during shoulder surgery.

Methods

Sixty-two patients underwent a computed tomography of the shoulder with a proximal humerus fracture. In the range of the glenoid apex, the ratios of the distribution of triangles with a Constant anterior and posterior area of the glenoid were measured. The location of glenoid apex was confirmed as the percentage of the position with respect to the upper part of the glenoid with the center of the part, analyzed the angle between the glenoid anterior surface and glenoid axis was measured.

Results

The angle between the glenoid anterior surface and glenoid axis was 19.80° ± 3.88°. The location of the glenoid apex is 60.36% ± 9.31%, with the upper end of the glenoid as the reference. The range of the glenoid apex was 21.16% ± 4.98%. When the height of the glenoid becomes smaller, the range of the glenoid apex tends to become larger (p=0.001) and the range of the glenoid apex becomes wider (p=0.001) as the glenoid width narrows.

Conclusions

We believe the anatomical measurements of the glenoid will be helpful for a more accurate insertion in glenoid component. It is thought that more accurate insertion is possible if we can set other anatomical measurements using computed tomography imaging of the glenoid which can develop into the study of other anatomical measurements.

Comparative analysis of 2 glenoid version measurement methods in variable axial slices on 3-dimensionally reconstructed computed tomography scans

BACKGROUND

Most glenoid version measurement methods have been validated on 3-dimensionally corrected axial computed tomography (CT) slices at the mid glenoid. Variability of the vault according to slice height and angulation has not yet been studied and is crucial for proper surgical implant positioning. The aim of this study was to analyze the variation of the glenoid vault compared with the Friedman angle according to different CT slice heights and angulations. The hypothesis was that the Friedman angle would show less variability.

MATERIALS AND METHODS

Sixty shoulder CT scans were retrieved from a hospital imaging database and were reconstructed in the plane of the scapula. Seven axial slices of different heights and coronal angulations were selected, and measurements were carried out by 3 observers.

RESULTS

Mid-glenoid mean version was -8.0° (±4.9°; range, -19.6° to +7.0°) and -2.1° (±4.7°; range, -13.0° to +10.3°) using the vault method and Friedman angle, respectively. For both methods, decreasing slice height or angulation did not significantly alter version. Increasing slice height or angulation significantly increased anteversion for the vault method (P < .001). Both interobserver reliability and intraobserver reliability were significantly higher using the Friedman angle.

CONCLUSION

Version at the mid and lower glenoid is similar using either method. The vault method shows less reliability and more variability according to slice height or angulation. Yet, as it significantly differs from the Friedman angle, it should still be used in situations where maximum bone purchase is sought with glenoid implants. For any other situation, the Friedman angle remains the method of choice.

Accuracy of patient-specific guided implantation of the glenoid component in reversed shoulder arthroplasty

BACKGROUND

The aim of this study was to assess the accuracy of patient-specific guided glenoid component implantation in reverse shoulder arthroplasty.

MATERIALS AND METHODS

32 reverse shoulder arthroplasties were done using preoperative 3D planning and 4 patient-specific guides to prepare the glenoid and position the glenoid component. Baseplate version, inclination and entry point as well as angulation of the screws were compared to the preoperative plan measured on CT by independent observers.

RESULTS

The mean deviation in baseplate version from the preoperative plan was 4.4°+3.1° (range, 0.3°-13.7°), in baseplate inclination 5.0°+4.2° (range, 0.1° to 14.5°) and in baseplate entry point 2.4mm+1.4mm (range, 0.4° to 6.3°). The average screw superior-inferior angulation deviation for the superior screw was 2.8°+2.6° (range, 0.0°-10.1°) and 2.8+2.6° in the antero-posterior plane (range, 0.1°-11.6°). For the inferior screw the superior-inferior angle deviation was 5.3°+3.8° (range, 0.1°-15.2°); the antero-posterior angle deviation was 4.1°+3.1° (range, 0.0°-9.8°).

CONCLUSIONS

Patient-specific instrumentation (PSI) for the glenoid component in reverse shoulder arthroplasty allows the shoulder surgeon to accurately execute the preoperative 3D plan.

LEVEL OF EVIDENCE

Level 3.

Impact of Modeling Assumptions on Stability Predictions in Reverse Total Shoulder Arthroplasty

Reverse total shoulder arthroplasty (rTSA) is commonly used in the shoulder replacement surgeries for the relief of pain and to restore function, in patients with grossly deficient rotator cuff. Primary instability due to glenoid loosening is one of the critical complications of rTSA; the implants are designed and implanted such that the motion between the glenoid baseplate and underlying bone is minimized to facilitate adequate primary fixation. Finite element analysis (FEA) is commonly used to simulate the test setup per ASTM F2028-14 for comparing micromotion between designs or configurations to study the pre-clinical indications for stability. The FEA results can be influenced by the underlying modeling assumptions. It is a common practice to simplify the screw shafts by modeling them as cylinders and modeling the screw-bone interface using bonded contact, to evaluate micromotion in rTSA components. The goal of this study was to evaluate the effect of three different assumptions for modeling the screw-bone interface on micromotion predictions. The credibility of these modeling assumptions was examined by comparing the micromotion rank order predicted among three different modular configurations with similar information from the literature. Eight configurations were modeled using different number of screws, glenosphere offset, and baseplate sizes. An axial compression and shear load was applied through the glenosphere and micromotion at the baseplate-bone interface was measured. Three modeling assumptions pertaining to modeling of the screw-bone interface were used and micromotion results were compared to study the effect of number of peripheral screws, eccentricities, and baseplate diameter. The relative comparison of micromotion between configurations using two versus four peripheral screws remained unchanged irrespective of the three modeling assumptions. However, the relative comparison between two inferior offsets and baseplate sizes changed depending on the modeling assumptions used for the screw-bone interface. The finding from this study challenges the generally believed hypothesis that FEA models can be used to make relative comparison of micromotion in rTSA designs as long as the same modeling assumptions are used across all models. The comparisons with previously published work matched the finding from this study in some cases, whereas the comparison was contradicting in other cases. It is essential to validate the computer modeling approach with an experiment using similar designs and methods to increase the confidence in the predictions to make design decisions.

Trabecular bone density distribution in the scapula relevant to reverse shoulder arthroplasty

Background

How trabecular bone density varies within the scapula and how this may lead to more optimal reverse shoulder arthroplasty (RSA) screw placement has not been addressed in the scientific literature. The 3 columns of trabecular bone within the scapula adjacent to the glenoid fossa, one extending through the lateral border, a second into the base of the coracoid process, and a third extending into the spine of the scapula, were hypothesized to be of relatively similar density.

Methods

Two-dimensional axial computed tomography (CT) images of 19 fresh frozen cadaver specimens were obtained. Digital Imaging and Communications in Medicine (DICOM; National Electrical Manufacturers Association, Rosslyn, VA, USA) image files of the CT scanned scapulae were imported into Mimics 17.0 Materialise Software (Leuven, Belgium) for segmentation and 3-dimensional digital model generation. To determine the distribution of trabecular bone density, Hounsfield unit (HU) values in the scapulae gray value files obtained from Mimics were filtered to remove any cortical bone. HU values of 650 define the corticocancellous interface in CT image data and were considered to be cortical bone. Analyses of variance with post hoc Bonferroni tests were used to determine statistical differences between the intra- and inter-regions of bone density comparisons.

Results

The base of the coracoid process was statistically significantly less dense than the spine and the lateral border of the scapulae examined (P < .05).

Discussion/Conclusion

The higher-quality bone in the spine and lateral border, compared with the coracoid regions, may provide better bone purchase for screws when fixing the glenoid baseplate in RSA.

Reverse total shoulder arthroplasty using helical blade to optimize glenoid fixation and bone preservation: preliminary results in thirty five patients with minimum two year follow-up

PURPOSE

Glenoid loosening is a common cause of reverse total shoulder arthroplasty (RTSA) failure, and grafting of the glenoid is often required for revision due to bone loss due to the central peg in most glenoid baseplates. Helical blades have been used in the hip to optimize bone fixation in proximal femoral fracture. This study presents the initial results of specifically designed helical blade in the shoulder to optimize glenoid bone fixation and preservation as part of RTSA.

METHODS

Thirty-five patients underwent RTSA with glenoid helical blade fixation. An uncemented glenoid baseplate was used with a central helical blade partially coated with hydroxyapatite and two or three screws. Outcome analysis was performed pre-operatively and at two years.

RESULTS

All patients were satisfied with the results and significant improvement was observed in functional outcome scores between baseline and final follow-up. There was a single intra-operative undisplaced glenoid fracture which did not compromise the baseplate fixation. There was no radiographic evidence of loosening or radiolucencies around the helical blade.

CONCLUSIONS

The helical blade provides a satisfactory primary fixation. Because of its length (21 mm), care should be taken in cases of pre-existing bone loss or sclerotic bone to avoid glenoid fracture or anterior cortical perforation. Helical blade has the potential to facilitate glenoid implant revision by preserving the glenoid bone stock.

Polyethylene dissociation from humeral stem status after reverse total shoulder arthroplasty

BACKGROUND

Reverse shoulder arthroplasty (RSA) is an important treatment option for 4-part proximal humerus fractures in the elderly and arthrosis of the glenohumeral joint with incompetence of the rotator cuff. Unique complications do occur with use of this type of prosthesis.

METHODS

We present 4 cases of polyethylene dissociation after RSA.

RESULTS

In a series of 549 patients who underwent RSA, the incidence of polyethylene dissociation was found to be 0.7%.

CONCLUSIONS

Polyethylene dissociation is a rare complication after RSA. Surgeons should be aware of this possibility if a closed reduction of an RSA dislocation is not possible.

Preoperative planning for accurate glenoid component positioning in reverse shoulder arthroplasty

BACKGROUND

Glenoid component positioning in reverse shoulder arthroplasty (RSA) is challenging. Patient-specific instrumentation (PSI) has been advocated to improve accuracy, and is based on precise preoperative planning. The purpose of this study was to determine the accuracy of glenoid component positioning when only the glenoid surface is visible, compared to when the entire scapula is visible on a 3D virtual model.

METHODS

CT scans of 30 arthritic shoulders were reconstructed in 3D models. Two surgeons then virtually placed a glenosphere component in the model while visualizing only the glenoid surface, in order to simulate typical intraoperative exposure ("blind 3D" surgery). One surgeon then placed the component in an ideal position while visualizing the entire scapula ("visible 3D" surgery). These two positions were then compared, and the accuracy of glenoid component positioning was assessed in terms of correction of native glenoid version and tilt, and avoidance of glenoid vault perforation.

RESULTS

Mean version and tilt after "blind 3D" surgery were +1.4° (SD 8.8°) and +7.6° (SD 6°), respectively; glenoid vault perforation occurred in 17 specimens. Mean version and tilt after "visible 3D" surgery were +0.3° (SD 0.8°) and +0.1° (SD 0.5°), respectively, with glenoid vault perforation in 6 cases. "Visible 3D" surgery provided significantly better accuracy than "blind 3D" surgery (P<0.05).

CONCLUSION

When the entire scapula is used as reference, accuracy is improved and glenoid vault perforation is less frequent. This type of visualization is only possible with pre-operative 3D CT planning, and may be augmented by PSI.

LEVEL OF EVIDENCE

Basic science study. Level III.

Reverse Shoulder Arthroplasty for the Treatment of 3 and 4- Part Fractures of the Humeral Head in the Elderly

Background:

Proximal humeral fractures in elderly patients present with severe comminution and osteoporotic bone quality.

Reverse shoulder arthroplasty has lately been proven beneficial in treating patients with complex proximal humeral fractures. The above technique is recommended and has better results in elderly than in younger individuals.

Methods:

We performed a literature search in the databases Pubmed, Medline, EMBASE and Cochrane Library for published articles between 1970 and 2016 using the terms: proximal humerus fractures and reverse shoulder arthroplasty.

Results:

Significant benefits with the use of reverse prosthesis, especially in patients older than 70 years with a proximal humeral fracture, include reduced rehabilitation time as well as conservation of a fixed fulcrum for deltoid action in case of rotator cuff failure.

Compared with hemiarthroplasty and internal fixation, reverse prosthesis may be particularly useful and give superior outcomes in older patients, due to comminuted fractures in osteopenic bones.

However, significant disadvantages of this technique are potential complications and a demanding learning curve.Therefore, trained surgeons should follow specific indications when applying the particular treatment of proximal humeral fractures and be familiar with the surgical technique.

Conclusion:

Although long-term results and randomized studies for reverse prosthesis are lacking, short and mid- term outcomes have given promising results encouraging more shoulder surgeons to use this type of prosthesis in proximal humeral fractures.

Optimizing baseplate position in reverse total shoulder arthroplasty in small-sized Japanese females: technical notes and literature review

The management of cuff tear arthropathy (CTA) has always been a challenge for shoulder surgeons. Introduction of reverse total shoulder arthroplasty (RTSA) helped in providing pain relief and improved shoulder function in patients with CTA. In this study, we aimed to evaluate the short-term clinical results and some clinical details regarding the types of available prosthesis, positioning, and size of the components for RTSA in a population of short-stature female Japanese. In our seven cases, the average glenoid size was 23.9 mm in width and 34.2 mm in height. The average width was smaller than the size of all available baseplates. We implanted reverse shoulder prostheses with baseplate that measured 28 mm in diameter and two locking screws. The center of the baseplate was shifted to allow slight anterior overhang relative to the anatomical center to avoid breakage of the posterior cortex and to achieve firm fixation. One case of humeral shaft fracture occurred while inserting the humeral stem and required encircling wiring. In our experience, the short term clinical results of RTSA were excellent, but a new prosthesis that is designed to fit the short stature of Asians with smaller glenoid and humerus should be considered.

Glenoid baseplate fixation using hybrid configurations of locked and unlocked peripheral screws

Background

The use of peripheral locked screws has reduced glenoid baseplate failure rates in reverse shoulder arthroplasty. However, situations may arise when one or more non-locked screws may be preferred. We aimed to determine if different combinations of locked and non-locked screws significantly alter acute glenoid baseplate fixation in a laboratory setting.

Materials and methods

Twenty-eight polyurethane trabecular bone surrogates were instrumented with a center screw-type glenoid baseplate and fixated with various combinations of peripheral locked and non-locked screws (1-, 2-, 3- and 4-locked con). Each construct was tested through a 55° arc of abduction motion generating compressive and shear forces across the glenosphere. Baseplate micromotion (μm) was recorded throughout 10,000 cycles for each model.

Results

All constructs survived 10,000 cycles of loading without catastrophic failure. One test construct in the 1-locked fixation group exhibited a measured micromotion >150 μm (177.6 μm). At baseline (p > 0.662) and following 10,000 cycles (p > 0.665), no differences were observed in baseplate micromotion for screw combinations that included one, two, three and four peripheral locked screws. The maximum difference in measured micromotion between the extremes of groups (1-locked and 4-locked) was 29 µm.

Conclusions

Hybrid peripheral screw fixation using combinations of locked and non-locked screws provides secure glenoid baseplate fixation using a polyurethane bone substitute model. Using a glenosphere with a 10-mm lateralized center of rotation, hybrid baseplate fixation maintains micromotion below the necessary threshold for bony ingrowth.

Level of Evidence

N/A/, basic science investigation.

Patient-Matched Implementation for Reverse Total Shoulder Arthroplasty

Introduction

Three-dimensional (3D) preoperative planning and patient-specific instrumentation (PSI) improve accuracy of glenoid component implantation in reverse shoulder arthroplasty.

Indications & Contraindications

Step 1 Preoperative Virtual 3D Planning Video 1

Use a 3D software tool for virtual preoperative planning of glenoid component implantation.

Step 2 Patient Positioning and Surgical Approach Video 2

Place the patient in a semi-beach-chair position and perform a standard deltopectoral approach.

Step 3 Humeral Preparation Video 3

Prepare the humeral side for implantation of the humeral component using standard instrumentation.

Step 4 Glenoid Exposure and Preparation Video 4

Expose the glenoid and prepare the glenoid surface for component implantation.

Step 5 Glenoid Preparation and Implantation of the Glenoid Baseplate Using 4 PSI Guides Video 5

Use the 4 PSI guides to prepare the glenoid for component implantation according to the preoperative plan.

Step 6 Definitive Implantation of the Components and Reduction Video 6

Implant the glenosphere and humeral component and reduce the prosthesis.

Step 7 Postoperative Rehabilitation Protocol

Start passive and active-assisted exercises immediately, and begin muscle strengthening and active exercises at 6 weeks.

Results

A recent prospective, comparative study assessed the influence of 3D preoperative planning and PSI guidance of glenoid component positioning in total shoulder arthroplasty and reverse shoulder arthroplasty¹⁸.

Pitfalls & Challenges

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

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

CT scan evaluation of glenoid bone and pectoralis major tendon: interest in shoulder prosthesis

Introduction: The shoulder arthroplasty brings satisfaction to patients in terms of quality of life and indolence. However whether anatomic implant or reverse, it does not escape from the loosening of the glenoid component. Moreover, optimal implantation is required to ensure the functional outcome without shortening of the arm. The purpose of this study is obtain CT scan evaluation of the glenoid bone stock in order to optimize glenoid component implantation and obtain a reference to determine optimal humeral component placement in case of humeral proximal fracture.

Materials and methods: Between 2010 and 2011 we have analyzed 200 intact shoulder’s CT. We measured maximal and minimal width in the transverse plane of the glenoid, the distance from the pectoralis major (PM) tendon to the humeral head, the greater tubercle, change of curvature and the anatomical neck.

Results: Mean maximum width was 27.4 ± 3.4 mm and mean minimum width was 15.5 ± 2.8 mm. Distances between upper edge of PM tendon to: humeral head, greater tubercle, change of curvature and anatomical neck were respectively: 67.6 ± 9.98 mm, 57.8 ± 10.3 mm, 28.7 ± 9 mm, and 34.2 ± 9.7 mm.

Conclusion: Our study has produced an assessment of glenoid bone stock for optimal positioning of the glenoid implant but also to obtain a reference to determine the ideal location of the humeral component in the case of proximal humerus fracture.

A patient-specific guide for optimizing custom-made glenoid implantation in cases of severe glenoid defects: an in vitro study

BACKGROUND

Glenoid component and screw malpositioning in cases of severe glenoid defects might result in complications. We examined the efficacy of a surgical method to treat severe glenoid defects, including a custom-made glenoid component and accurate screw positioning, using a patient-specific positioning guide.

METHODS

Glenoid defects were created in 10 cadaveric shoulders. Computed tomography images were used to plan reversed shoulder arthroplasty and design patient-specific glenoid components. A patient-specific positioning guide was designed for 5 specimens. The remaining 5 specimens were implanted without the guide. Computed tomography images were used to determine the postoperative glenoid component and screw positions. Differences from the preoperatively planned implant and screw positions were calculated.

RESULTS

The patient-specific positioning guide significantly reduced the angular deviations from the planned glenoid implant positioning (P < .05) and also significantly improved the positioning of the screws (P < .001). In the group without the guide, the average total intraosseous screw length was 52% of the ideal preoperatively planned length compared with 89% for the group with the guide. A strong correlation (r = -0.85) was found between the orientation of the implant and the postoperative total intraosseous screw length.

CONCLUSIONS

A patient-specific positioning guide significantly improves the position and fixation of a custom-made glenoid component in cases of severe glenoid defects.

Optimal baseplate rotational alignment for locking-screw fixation in reverse total shoulder arthroplasty: a three-dimensional computer-aided design study

BACKGROUND

Baseplate loosening in reverse total shoulder arthroplasty (RTSA) remains a concern. Placing peripheral screws into the 3 pillars of the densest scapular bone is believed to optimize baseplate fixation. Using a 3-dimensional computer-aided design (3D CAD) program, we investigated the optimal rotational baseplate alignment to maximize peripheral locking-screw purchase.

METHODS

Seventy-three arthritic scapulae were reconstructed from computed tomography images and imported into a 3D CAD software program along with representations of an RTSA baseplate that uses 4 fixed-angle peripheral locking screws. The baseplate position was standardized, and the baseplate was rotated to maximize individual and combined peripheral locking-screw purchase in each of the 3 scapular pillars.

RESULTS

The mean ± standard error of the mean positions for optimal individual peripheral locking-screw placement (referenced in internal rotation) were 6° ± 2° for the coracoid pillar, 198° ± 2° for the inferior pillar, and 295° ± 3° for the scapular spine pillar. Of note, 78% (57 of 73) of the screws attempting to obtain purchase in the scapular spine pillar could not be placed without an in-out-in configuration. In contrast, 100% of coracoid and 99% of inferior pillar screws achieved full purchase. The position of combined maximal fixation was 11° ± 1°.

CONCLUSIONS

These results suggest that approximately 11° of internal rotation is the ideal baseplate position for maximal peripheral locking-screw fixation in RTSA. In addition, these results highlight the difficulty in obtaining optimal purchase in the scapular spine.

Biomechanics of reverse total shoulder arthroplasty

Reverse total shoulder arthroplasty is an effective procedure for treatment of glenohumeral joint disease among patients with severe rotator cuff deficiency. Improvements in prosthetic design are the result of an evolved understanding of both shoulder and joint replacement biomechanics. Although modern generations of the reverse shoulder prosthesis vary in specific design details, they continue to adhere to Grammont's core principles demonstrated by his original Delta III prosthesis. This review article discusses the biomechanics of reverse total shoulder arthroplasty with a focus on elements of implant design and surgical technique that may affect stability, postoperative complications, and functional outcomes.