Stress Fractures After rTSA. Not Every Onlay is Created Equal.

Ian Byram, MD

Read complete study: Increased scapular spine fractures after reverse shoulder arthroplasty with a humeral onlay short stem: an analysis of 485 consecutive cases

Since its FDA clearance in 2003, reverse shoulder arthroplasty (RSA) has become increasingly utilized for the treatment of arthritis, fractures, and rotator cuff failures in the United States. Initial reports demonstrated a high rate of complications, including instability, impingement, scapular notching, and subsequent implant failure.Many implant designs have been successfully modified to minimize these problems. While scapular notching seen with the initial Grammont style prosthesis has decreased with modern lateralized implant designs, scapular spine fractures have become more prevalent.

The authors of this study analyzed a series of RSA cases utilizing a short stem, 145° neck-shaft inclination prosthesis hoping to shed light on implant features that may lead to scapular spine fractures. In a retrospective review of 485 consecutive arthroplasties, they reported 21 (4.3%) scapular spine fractures that were diagnosed at a mean of 8.6 months after surgery. Comparing those patients with matched controls, patients with fractures demonstrated significantly worse Constant scores and forward flexion. They concluded that utilization of a lateralized “onlay” convertible humeral design creates increased stress on the deltoid and acromion, resulting in an undesirable rate of scapular spine and acromial fractures.

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Scapular Fractures After RSA – The Bane of Our Existence

Stephanie Muh, MD

Read complete study: Scapular fracture in reverse shoulder arthroplasty (Grammont Style): prevalence, functional, and radiographic results with minimum 5-year follow up

The development of postoperative scapular spine or acromial base fractures remains a difficult problem to treat. With a reported incidence of 1-10% in the literature, there has been no consensus on the best treatment, and most authors report poor post-fracture functional outcomes.1-3 Both operative and nonoperative management of these fractures have been advocated with variable outcomes.2,3

This retrospective study presents data from a large cohort of patients with a single prosthetic design (Grammont style with medialized center of rotation and medialized humerus with inlay prosthesis). The authors found an overall prevalence of 1.3% scapular fractures in 1,953 implants. This seems to correlate with other literature where the incidence ranged from 1-10%.1-4 When evaluating the functional results with a minimum of five years follow-up, 19 fractures were identified with an overall improved range of motion and Constant score. It is important to note, however, the patients with fractures did not improve as greatly as those without fractures. While the postoperative Constant score improved from 25.6 to 47 postoperatively, the authors note the average postoperative Constant score in a non-fracture group is 70. They did not directly compare the fracture group range of motion to non-fracture group which I think would have added valuable information. It would have been interesting if the authors presented initial improvement postoperatively and compared this to post-fracture outcomes and commented if there was function.

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To Repair, or Not to Repair, That is the Question…

Kaveh Sajadi, MD

Read complete study: The effect of subscapularis repair on dislocation rates in reverse shoulder arthroplasty: a meta-analysis and systematic review

Whether ‘tis nobler in the mind to bear the slings and arrows of our colleagues…

The role of the subscapularis in reverse total shoulder arthroplasty (rTSA) continues to be debated. Reverse TSA is most commonly performed via a deltopectoral approach, which often requires takedown of an intact, though possibly degenerated or atrophic, subscapularis tendon. Surgeons debate the importance of its repair at the conclusion of the surgery. This debate centers on the importance and role of the subscapularis in stability of the prosthesis, range of motion (both internal and external rotation), and outcomes. Those in favor of repair cite studies indicating lower dislocation rates with repair and better internal rotation; those opposed express concern about it potentially limiting external rotation and possibly opposing the deltoid in elevating the arm.1 This meta-analysis and systematic review sought to compare the dislocation rates and outcomes in rTSA with and without subscapularis tendon repair using the highest level of data available.

This meta-analysis and systematic review sought to compare the dislocation rates and outcomes in rTSA with and without subscapularis tendon repair using the highest level of data available.

It is important to clarify some descriptions used in the study. Since the introduction of the original Grammont style reverse prosthesis in the late 1980s and early 1990s, many different design modifications have been introduced.2 The primary differentiating characteristic between implant designs is the location of the center of rotation (COR) of the new glenohumeral articulation. By their very nature, all reverse designs medialize the COR compared with the native shoulder. However, systems with the COR at the glenoid face, as the original Grammont design, are considered medialized and those with the COR lateral to the glenoid are referred to in this paper as lateralized designs. Furthermore, the implant can have a medialized humerus (Grammont) or a lateralized humerus. Routman HD, et al, proposed a classification to standardize the nomenclature, dividing implants into the medial glenoid/medial humerus (Grammont), lateral glenoid/medial humerus, and medial glenoid/lateral humerus.2,3 Some of the implants in this study, classified as lateralized glenoids by the authors, are classified as medial glenoid/lateral humerus by Routman.

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Instability Remains a Leading Cause of Complications in Reverse Shoulder Arthroplasty

Moby Parsons, MD

Read complete study: Analysis of 4063 complications of shoulder arthroplasty reported to the US Food and Drug Administration from 2012 to 2016

In this article, Somerson and colleagues queried the Manufacturer and User Facility Device Experience (MAUDE) database for failure modes of anatomic and reverse shoulder arthroplasty. The authors identified 2,390 reports on reverse total shoulder arthroplasty of which 32% were for dislocation/instability. This was more than twice the rate of the next most commonly reported complication of infection at 13.8%. This rate concurred with findings by Bohsali et al1 who reported 31.2% of reverse shoulder complications due to instability in an analysis of published reports.

However, given that most complications are not reported in the medical literature, the actual incidence of dislocation is not known and may be higher. Risk factors have included higher body mass index, fracture sequelae, axillary nerve injury, soft tissue and bone impingement, improper implant placement, and inadequate soft tissue tension. The role of the subscapularis in reverse arthroplasty stability is controversial with some reports of a higher risk of dislocation in the subscapularis deficient shoulder and other reports of no difference in instability rates regardless of integrity. In general, instability after reverse shoulder arthroplasty occurs relatively early in the postoperative setting and often requires revision surgery. It remains a substantial problem.

In general, instability after reverse shoulder arthroplasty occurs relatively early in the postoperative setting and often requires revision surgery. It remains a substantial problem.

Prosthesis design may play a role in instability although the effect of design parameters on stability biomechanics has not been fully defined. In this report, the two designs with the highest dislocation percentage are both humeral inlay designs. Considering that some cases of instability occur from bone or soft tissue impingement, particularly in adduction, it stands to reason that onlay designs which provide humeral lateralization may be less at risk for this problem. For example, the  Equinoxe® shoulder system, which is an onlay system with a 145° neck/shaft angle, has shown low rates of scapular notching compared to traditional Grammont-style designs which are inlay systems with a 155-degree neck shaft angle.2  Glenosphere lateralization may also reduce this risk of instability.3 The Equinoxe shoulder system provides lateralized glenospheres, which when combined with an eccentric baseplate, may help protect against postoperative dislocation. The ExactechGPS® Shoulder Application’s preoperative planning tool and ExactechGPS® intraoperative navigation can also be used to improve implant position, and in cadaveric studies have shown to increase implant accuracy and precision when used together.4

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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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