CT-Based Intraoperative Navigation for Glenoid Placement in TSA

Moby Parsons, MD

3D imaging technology has led to a much better understanding of glenoid morphology and how it is affected by the wear process in shoulder arthritis. The pathologic triad as described by Matsen1 (1. posterior humeral subluxation; 2. increased glenoid retroversion; 3. biconcave glenoid) is encountered in many arthritic shoulders. Other wear patterns like superior erosion may also commonly occur in certain conditions like cuff tear arthropathy. One of the principle goals of shoulder replacement, whether anatomic or reverse, is to recognize and correct pathologic glenoid deformity as failure to do so may risk premature loosening of the glenoid implant due to abnormal loading mechanics.

Unfortunately, even experienced shoulder surgeons do a poor job in correcting glenoid erosion. A meta-analysis by Sadoghi et al demonstrated an average error in glenoid correction of +/- 11 degrees2. Other research by Iannotti et al showed an angular variability of 10 degrees in pin placement using a free-hand technique3.

Advanced CT imaging has allowed surgeons to preoperatively plan the placement of the glenoid component with the goal of correcting pathologic version, minimizing bone loss and preventing penetration of the glenoid vault.

This lack of precision is no longer acceptable given today’s technology. Advanced CT imaging has allowed surgeons to preoperatively plan the placement of the glenoid component with the goal of correcting the pathologic version, minimizing bone loss and preventing penetration of the glenoid vault. As many systems now offer augmented glenoid implants, such systems also allow selection of the optimal implant for each given case. Research looking at the ability of surgeons to recreate a preoperative plan using conventional, free-hand instruments compared to surgical navigation has been performed. The results demonstrate that even with planning, a surgeon’s ability to execute that plan remains very inaccurate. The scatter plot above shows the range of implantation variability without navigation in blue compared to with navigation in orange. These results clearly show that eye-balling it in the operating room is no longer acceptable with today’s technology.

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The Effect of Lateralization on the Rotator Cuff Following Reverse Shoulder Arthroplasty

Stephanie Muh, MD

Read complete study: Clinical Outcomes after Reverse Shoulder Arthroplasty with and without subscapularis repair: The Importance of considering glenosphere lateralization

There continues to be significant debate on whether subscapularis repair is necessary during reverse total shoulder arthroplasty. Historically subscapularis repair was felt to be necessary to provide anterior soft tissue stability and help prevent post-operative dislocation. There have been multiple articles written on both the advantages and disadvantages of subscapularis repair. It should be noted that most previous articles that strongly advocated subscapularis repair included the traditional Grammont-style prosthesis with a medialized glenosphere and valgus medialized humeral stem (155 degrees).

This article retrospectively reviews patients who underwent reverse total shoulder arthroplasty (RTSA). They first stratified the subscapularis repair group versus no repair. The authors then looked at the effects of glenosphere lateralization (0mm lateralization vs +3 or +6mm) in both groups to determine if this played a significant role. The humeral stem used in the study has a neck shaft angle of 147 degrees but a humeral stem with no lateralization. ASES score from baseline was the primary outcome measured with a minimum of two-year follow-up.

The study demonstrated patients with no subscapularis repair and lateralization had the most overall improvement in ASES scores. This supports the design rationale of the Equinoxe® reverse shoulder system.

Overall, the authors found no difference in ASES scores when comparing subscapularis repair versus no repair. The authors also reported that subscapularis management and lateralized glenosphere individually did not have significant effect on ASES scores. However, analysis did find that patients with subscapularis repair with a lateralized glenosphere did worse compared to subscapularis repair with medialized glenosphere and no repair with lateralized glenosphere.

This article demonstrates the impact of the combined effect of subscapularis management with glenosphere lateralization on clinical outcomes. The study demonstrated patients with no subscapularis repair and lateralization had the most overall improvement in ASES scores. This supports the design rationale of the Equinoxe® reverse shoulder system. Continue reading

My Experience with Trabecular Metal-Backed Glenoids

Ian Byram, MD

Read complete study: Outcomes of Trabecular Metal-backed glenoid components in anatomic total shoulder arthroplasty.

The authors of this study present a series of 47 total shoulder arthroplasties performed with trabecular metal-backed glenoid components, reporting radiographic and clinical outcomes at an average follow-up of 41 months.  The operative technique described involved placement of a trabecular metal peg-keel construct, with the vast majority placed in an uncemented, press-fit fashion.  The authors noted that this method of implantation is not approved by the FDA, but this technique is “acceptable practice.”  Patients were placed into a sling for four weeks and external rotation was limited for six weeks.

Five of the 47 patients (11%) underwent revision to reverse TSA for rotator cuff failure at an average of 12 months postoperative and were not included in the radiographic analysis.  Despite excluding these patients, the authors still report an alarming rate of metal debris and osteolysis (25%) with one catastrophic failure at a minimum of two years follow-up.  Notably, the majority of patients with radiographic changes were asymptomatic.  For all revisions in this series, the authors note the “substantial central bone loss” in the glenoid vault, requiring bone grafting for reverse baseplate implantation.  As a result of the high rate of metallic debris and osteolysis, the authors have discontinued the use of the trabecular metal glenoid.

“The authors still report an alarming rate of metal debris and osteolysis (25%) with one catastrophic failure at a minimum of two years follow-up.

For a short period of time in my practice, I utilized this same trabecular metal backed glenoid.  Preparation for this implant requires perpendicular glenoid exposure and removal of bone from the central glenoid vault in a cross shape with a series of drill holes and punches.  In my experience revising this implant, I also have noted severe central bone loss requiring bone grafting and occasional staged reconstruction.

Similar to the authors of this study, I had one catastrophic failure in a 50 year old male with normal bone density and no comorbidities.  Continue reading

Revision with a Platform System

Alberto Rivera, MD

Read complete studies:

Conversion to reverse shoulder arthroplasty: humeral stem retention versus revision

Platform shoulder arthroplasty: a systematic review

The number of shoulder arthroplasty procedures is rapidly increasing. Therefore, shoulder revision is becoming a commonly performed procedure. Historically revising a hemiarthroplasty or total shoulder replacement ended up in a hemiarthoplasty, resection arthroplasty, arthrodesis or more recently reverse arthroplasty. This type of revision usually required stem removal, which could potentially lead to humeral fracture with or without the need of an osteotomy, increasing surgical time, bleeding and neural damage.  Also, late complications, such as osteotomy nonunion and malunion could develop. Another important factor to take into consideration is the added cost of using additional implants such as a new stem, cement, cables or allograft in the setting of humeral stem revision. Modular implants using a platform system allows for a faster revision with fewer complications and potentially less cost.

“Recent publication by Williams and Colleagues (1) reported on 17 patients who underwent modular conversion and nine who had revision of humeral stem. Pain, stability and ASES scores improved significantly.”

I believe the use of modular platform in primary shoulder arthroplasty either hemi or total should be the standard of care.

In my experience, revising TSA to RSA has evolved to a more straightforward procedure with the use of modular components of the platform shoulder type. I believe the use of modular platform in primary shoulder arthroplasty either hemi or total should be the standard of care.

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Optimizing Mini-stem Humeral Component Design in Shoulder Arthroplasty

Thomas Obermeyer , MD

Read complete study: Proximal ingrowth coating decreases risk of loosening following uncemented shoulder arthroplasty using mini-stem humeral components and lesser tuberosity osteotomy

Innovation in shoulder arthroplasty prosthesis design has led to a paradigm shift in recent years to “platform” (convertible) humeral stems that obviate the need for stem extraction when converting between non-constrained anatomic total shoulder arthroplasty and reverse arthroplasty.1  Paralleling this has been a transition to mini stems that shift the location of humeral fixation from the diaphysis to the metaphysis (Figure 1).  Shorter, metaphyseal-fixing stems preserve humeral bone stock and eliminate the need for diaphyseal fixation, which eases revision and may improve long-term fixation.  Mini humeral stems have performed well in short-term follow-up studies and achieve the very favorable pain relief and functional improvement expected in total shoulder arthroplasty.2

Fig 1. Platform mini humeral stems can be converted from nonconstrained to reverse arthroplasty without resecting a well fixed stem. This stem has proximal porous coating and aggressive tapering to maximize proximal fixation.

The potential benefits of mini humeral stems are numerous.  More proximal metaphyseal fixation may eliminate the need for extended humeral osteotomy when extraction is necessary and retain native distal metaphyseal and diaphyseal bone for subsequent fixation in the revision setting.  Shorter stems may also diminish stress shielding, where the bone surrounding the proximal portion of the prosthesis remains relatively unloaded, leading to proximal bone resorption which may jeopardize long term fixation.3  Periprosthetic fracture management is often easier and shorter stems have greater applicability to preexistent humeral conditions such as post-fracture deformities and insertion above a total elbow arthroplasty.

Until recently there has not been evidence to guide specific mini stem prosthesis design.  Original mini stem designs were uncoated and had high rates of radiolucent lines and clinical loosening.4,5 The recent article by Morwood et al suggests that adding proximal porous coating to mini humeral stems may improve on early uncoated designs, with improved rates of loosening and proximal radiolucent lines.  Despite short term follow-up at two years, their retrospective analysis saw a significantly lower rate of proximal radiolucent lines and no clinical loosening in proximally coated mini humeral stems.  These are promising results.

Time will tell if recent design innovations to humeral mini stems will generate improvements in long-term shoulder replacement outcomes, but I remain optimistic.

Perhaps a concerning finding in Morwood’s study was that despite the improved fixation observed at two years with proximal porous coating, there was a 21% rate of radiolucencies.  This is slightly worrisome as the study sample size is small and two years is relatively short term follow-up in an arthroplasty study.  Will the radiolucencies progress to clinical loosening if the follow-up is prolonged to five or ten years?  This begs the question: can humeral component design be improved yet again so that, despite proximal coating, an even lower rate of radiolucent lines may be observed?  My hypothesis is yes, based on 1) generating more substantial carve-outs in the stem so that the prepared metaphyseal bone will permit improved rotational stability immediately at the time of press-fitting (Figures 2 and 3), 2) producing a more aggressive proximal press-fit so that proximal cancellous bone is more substantially loaded and the reliance on fixation at more distal metaphyseal bone is minimal, 3) avoiding distal contact of the stem with the humeral cortex, which will accelerate stress shielding (Figure 1).   Time will tell if recent design innovations to humeral mini stems will generate improvements in long-term shoulder replacement outcomes, but I remain optimistic.

Fig. 2. A potential design with more substantial carve-outs in the mini stem and aggressive tapering that maximizes proximal fixation may improve on the rate of radiolucencies observed in the Morwood study.

Fig. 3. Immediate rotational stability may be achieved by carve-outs in the broach and stem that leave this pattern of prepared cancellous bone.

 

References:
1. Crosby et al. Conversion to Reverse Total Shoulder Arthroplasty with and without Humeral StemRetention: The Role of a Convertible-Platform Stem. J Bone Joint Surg Am. 2017 May 3;99(9):736-742.
2. Harmer et al. Total shoulder arthroplasty: are the humeral components getting shorter? Curr Rev Musculoskelet Med 2016;9:17-22.
3. Raiss et al.  Radiographic changes around humeral components in shoulder arthroplasty. J Bone Joint Surg Am. 2014 Apr 2;96(7):e54.
4. Casagrande et al. Radiographic evaluation of short-stem press-fit total shoulder arthroplasty: short-term follow-up. J Shoulder Elbow Surg. 2016;25:1163-9.
5. Schnetzke et al. Radiologic bone adaptations on a cementless short-stem shoulder prosthesis. J Shoulder Elbow Surg 2016;25:650-7.

Thomas Obermeyer, MD, is a board-certified and fellowship-trained orthopaedic surgeon in Illinois, specializing in shoulder and elbow reconstruction and sports injuries. Dr. Obermeyer received his medical degree from Albany Medical College and completed his residency at Loyola University Medical Center in Chicago. He went on to complete a fellowship in shoulder and elbow at Mount Sinai Medical Center in New York City. Dr. Obermeyer is also an award-winning researcher and published author.​

How Should We Approach Superior Glenoid Wear?

Kevin Famer, MD

Read complete study: Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss

In the article “Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss” by Martin et al, the authors looked to quantify glenoid baseplate stability with worsening superior glenoid bone loss.  The authors utilized a polyurethane bone model, and created superior glenoid bone loss defects such that the attached baseplates had 100% support, 90% support, 75% support, and 50% support.  The authors found the 50% support group had significantly greater micromotion than the other defects and the native state.  The majority of micromotion occurred at the beginning of testing, indicating that some settling may occur with time.  Interestingly, micromotion in the 50% support group exceeded 150 µm, which has been shown in animal models to be the maximum amount of micromotion that allows bony ingrowth.

The authors spend a lot of time describing their testing methods, compared to other published manuscripts.  The authors applied cyclic loading at a fixed 60º glenohumeral angle, which mimics the superiorly directed force during the initiation of abduction, as opposed to other studies that apply force to the baseplate that mimics the force during the range of abduction.  The benefits of the study design of this current study is that it allows real time assessment of micromotion during the course of the analysis, as well as pre and post testing, potentially allowing a better assessment of micromotion early in the loading process.

The information presented in this study is valuable in the sense that using real time of assessment of micromotion, the authors find that increasing superior glenoid wear leads to increasing superior micromotion early in the loading process.  There also appears to be some settling over time, but the issue failure of early bony integration, and its association to loosening over time, is a concern.  Surgeons should be aware of results of this study, and the potential risk of glenoid loosening with uncorrected superior glenoid wear.

When approaching superior glenoid wear, surgeons have three main options.

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How Do I Manage Glenoid Bone Loss?

Read complete study: Bone Graft Augmentation for Severe Glenoid Bone Loss in Primary Reverse Total Shoulder Arthroplasty

Kaveh R. Sajadi, MD

Following the legacy of hip and knee replacements in relieving pain and improving function for patients with arthritis, shoulder replacements are now the fastest growing joint replacement. Shoulder replacements reliably improve the quality of life for most patients and approximately 85% are still in place 15 years later. The leading cause of failure is loosening of the component on the glenoid side of the shoulder. Minimizing this improves longevity and outcomes.

Shoulder arthritis is often characterized by significant glenoid bone loss. Classically, primary arthritis is associated with posterior glenoid wear, while rotator cuff tear arthropathy leads to superior glenoid wear. To minimize the risk of glenoid loosening, it is important to restore glenoid alignment and version and obtain secure fixation. The surgeon may be faced with managing diminished bone stock or significant deformity to achieve these goals. The primary options for managing bone loss on the glenoid side are eccentric reaming, bone grafting, and augmented glenoid implants.

In “Bone Graft Augmentation for Severe Glenoid Bone Loss in Primary Reverse Total Shoulder Arthroplasty,” Dr. Lorenzetti and his coauthors have reported their outcomes with one of these approaches, bone grafting, in conjunction with reverse shoulder arthroplasty.  The authors had two goals: first, to determine the outcome of reverse arthroplasty when bone grafting was performed as part of a primary procedure; second, to correlate outcomes with the amount of native bone support at implantation. They conducted a retrospective of 57 patients with minimum 2-year follow up who had this procedure done.

In addition, they used CT scans preoperatively and plain radiographs postoperatively to measure the degree of bone loss and the amount of native bone support under the glenoid baseplate. Replacements were performed for rotator cuff tear arthropathy, rheumatoid arthritis, osteoarthritis, and chronic dislocations. Due to the diversity of diagnoses, the wear pattern varied.  ASES, Simple Shoulder Test, VAS pain and function scores, and patient satisfaction were assessed at minimum 2-year follow up.

Intraoperative decision making determined that if at least 80% of contact could not be achieved between the baseplate and native glenoid, bone grafting was utilized. When available and of sufficient quality, humeral head autograft was preferentially used. Otherwise, femoral head allograft was chosen. Virtual models of the bone and implant were created based on preoperative CT and postoperative x-rays and used for virtual implantation to determine the baseplate contact with native bone, which was reported as a percentage of total surface area available. A previously performed cadaveric study was used as a validation for this virtual technique.

The authors reported significant improvements in ASES scores, patient satisfaction, simple shoulder test, range of motion, and pain scores. Further, they documented graft incorporation in 98% of patients. The mean contact area percentage of the implant on native bone was 17%. They did not find an association of outcome with bone contact area.

I commend the authors on their technique and outcomes. Their high incorporation rate and low failure rate show that bone grafting for significant glenoid defects is a successful technique. It is important to consider some factors not specifically mentioned though.

First, restoration of normal glenoid alignment is an important goal of reverse arthroplasty, and the authors do not report pre- or postoperative version. Second, graft preparation and sizing should optimize this restoration and shaping the glenoid bone graft can be challenging. Finally, although contact with native bone is measured, the amount of fixation of the implant into native bone is not described. The implant must make significant purchase, generally a centimeter or more, in the native glenoid, often through the graft, to achieve stable fixation. Having a long central post/cage or screw facilitates this.

I have performed this technique with success as well. The pictures below are of a 71-year-old gentleman with a Walch B2 glenoid with approximately 25 ° of posterior glenoid wear. I chose to use humeral head autograft with a long central post implant to insure fixation in native bone. Preoperative and postoperative imaging are included.

Pre-op

Post-op

While this paper describes one particular method, it is important to remember there are other ways to manage glenoid bone loss.  Continue reading

What Options Are Available for Extensive Proximal Humeral Bone Loss?

Stephanie Muh, MD

Read complete study:  Radiographic changes and clinical outcomes associated with an adjustable diaphyseal press-fit humeral stem in primary reverse shoulder arthroplasty

The use of press-fit humeral components for reverse shoulder arthroplasty has become more common in shoulder replacement surgery.  Historically, humeral fixation was achieved with cementation techniques.  However, due to increased operating time for cementation and added difficulty with higher complications in revisions during humeral component removal, surgeons have increasingly transitioned to press-fit humeral stems.

This article is a retrospective review of primary reverse shoulder replacements implanted with a modular diaphyseal press-fit humeral stem.  Total hip literature has shown that distal press-fit stems obtain control through the medullary canal.  The torsional stress is then transferred to proximal fixation and leads to increased stress shielding proximally with corresponding bone loss.  This seems to be demonstrated in this study as well.  With only a short-term follow-up, the authors found minimal radiolucent lines around distal fixation.  However, 97% of radiographs demonstrated radiolucent lines around the smooth metaphyseal component. Additionally, the authors found progression of these radiolucent lines during the first two years.  The authors claim the radiolucent line progression stabilizes after two years, however their mean follow up was 42 months (three and a half years).  I do not believe this is sufficient time to truly access whether evidence of radiolucent lines has stabilized.

The evidence of proximal humeral bone loss is concerning and brings up an interesting clinical question. How do we revise shoulders with massive proximal bone loss? Continue reading

How Can We Improve Accuracy in TSA?

Ian Byram, MD

Read complete study: Comparison of patient-specific instruments with standard surgical instruments in determining glenoid component position: a randomized prospective clinical trial

The authors of this randomized clinical study compared 15 anatomic total shoulder arthroplasties performed with patient-specific instrumentation to 16 aTSA cases performed with standard surgical instrumentation.  Preoperative three-dimensional CT scan images were utilized in both groups to plan the desired implant position, then postoperative CT scans were performed to measure the differences between the intended and actual glenoid implant position.  The authors reported improved accuracy of the PSI group with statistically significant decreases in mean deviation of inclination and medial-lateral offset as compared to the standard group. Mean deviation in version was 4.3° ± 4.5° for the PSI group as compared to 6.9° ± 4.4° in the standard surgical group (p=0.11), with significant improvement in version accuracy in patients with preoperative retroversion in excess of 16°. The authors conclude that surgical accuracy is improved by patient specific instrumentation when compared to standard surgical instrumentation, with greatest benefit occurring in patients with severe glenoid deformity.

As technology continues to progress, we will have increased opportunities to improve surgical accuracy in shoulder arthroplasty implant positioning.  These are exciting times, but it is our duty to balance cost and utility with progress.  The current study brings up several interesting points that impact my practice:

  1. Preoperative planning with three-dimensional imaging has greatly improved our knowledge and performance in glenoid implant positioning
  2. Intraoperative instrumentation and/or guidance does improve accuracy
  3. The desired correction of retroversion remains undetermined

By preoperatively templating, I can more reliably enact a surgical plan to meet the needs of my patients, and this should be considered standard of care in shoulder arthroplasty.

Regarding preoperative planning, I routinely obtain preoperative CT scans with three dimensional reconstructions on nearly all shoulder arthroplasty candidates.  The arthritic glenoid does not wear in two dimensions but often with subtle variations that may not be obvious on axillary radiographs or even axial CT cuts alone.  By preoperatively templating, I can more reliably enact a surgical plan to meet the needs of my patients, and this should be considered standard of care in shoulder arthroplasty. In patients with a central wear pattern that have already obtained an MRI to assess the integrity of the rotator cuff I will consider planning based on this study alone, but this is generally only for cost purposes or patient convenience.

With regard to the second point, this study shows how intraoperative guidance can improve accuracy in glenoid positioning, with the greatest benefit seen in patients with severe deformity.  It has been shown numerous times that anatomic placement of implants leads to improved clinical outcomes in shoulder arthroplasty. Intraoperative guidance can be in the form of PSI (as seen in this study), custom implants, or computer guided intraoperative navigation.  In my practice, I have begun to implement CT guided navigation for glenoid implantation.  PSI and computer navigation both offer the ability to improve accuracy, but PSI does not allow for intraoperative corrections such as conversion to reverse arthroplasty or difficulty applying the PSI guide due to anatomical constraints.  In this study, 3 of the 44 patients initially enrolled for anatomic TSA underwent reverse TSA, eliminating them as candidates for PSI.

As an example, the following case is a 67 year old male with a retroverted glenoid and intact rotator cuff based on exam and preoperative imaging.

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What are the Benefits of CAOS for Shoulder Replacement?

Ari R Youderian, MD

Read complete study: Benefit of intraoperative navigation on glenoid component positioning during total shoulder arthroplasty

I have now performed my first 40 shoulder replacement cases with computer assisted orthopaedic surgery (CAOS).  As an early adopter of this technology, the meta-analysis by Sadoghi et al, “Benefit of intraoperative navigation on glenoid component positioning during total shoulder arthroplasty” was very intriguing to me.  The authors reveal seven cases of comparative studies between CAOS and standard shoulder replacement.  The biggest finding was a combined 6 degree difference in glenoid version, but they found limited data and differences in inclination or other parameters.  The study emphasizes the point that navigation will continue to demonstrate improved accuracy in postoperative position, but we are only scratching the surface with the power of this technology.  As a fairly high volume shoulder surgeon, even I can easily see a difference in glenoid placement, angulation and screw positions as I compare my postoperative radiographs from my navigated cases to my pre-navigation cases.

The good news is that CAOS for shoulder replacement is finally here.  This is not the same as patient specific instrumentation; it’s a step further.  The newest CAOS system allows for robust planning, continuous feedback to the surgeon throughout the case and the ability to deviate from the plan but still always know where you are.  The authors make a great point about the added benefit of both accuracy and reliability.  Not only do these systems allow you to place a glenoid within 1mm and degree of your plan, but they will commonly decrease the margin of error.  This is a common theme of eliminating outliers, seen with the knee CAOS systems, especially for those who perform these cases less often.

During my fellowship, CAOS was not available.  My mentor was finishing up his work on the first patient specific navigation system, and we used a robust 3-D planning tool.  I quickly bridged the gap between the standard radiograph and 2-dimensional planning seen in residency to the eye-opening concepts of 3-D, including planning and implementation of glenoid sizing, seating, use of augmented implants, finding the best bone for fixation and bone graft planning in severe deformity cases.

Preoperative planning software has allowed me to more accurately choose glenoid sizes and augmentation, as well as estimate the patient’s native glenoid position.

Since that time, these concepts have permeated in each case that I carefully planned, but I did not have the tools to translate them to the operating room.  Previous studies have demonstrated that the use of preoperative planning software alone adds to the accuracy of glenoid placement.  Preoperative planning software has allowed me to more accurately choose glenoid sizes and augmentation, as well as estimate the patient’s native glenoid position.  In addition, augmented glenoids are much easier to place with CAOS, as the guessing of how much bone to remove and at what angle to start are removed from the equation.  The majority of my decision making is now performed prior to the start of the surgery, and it is then executed more promptly and efficiently during the surgery.

One important clarification that this study does not address is the difference between cadaver studies, virtual studies and in vivo studies.

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