The semiconstrained reverse shoulder prosthesis, designed by Grammont in the late 1980s was invented based on 2 biomechanical concepts: lowering the humerus and medialization of the center of rotation at the glenoid component. This design has the dual advantage oftensioning the deltoid muscle to increase its functional strength, and decreasing mechanical torque at the glenoid component, thus avoiding glenoid loosening.
The first series of reverse shoulder arthroplasty (RSA) with at least 2 years of follow-up confirmed the preliminary results, with excellent functional outcome and stable glenoid fixation. However, these series had a small numbers of patients and reported variable complication and revision rates of 15% to 50% and reoperation rates of 4% to 40%. One reason for the high variability was unclear definitions of complications and revisions, which varied markedly between the series.
A study attached at the bottom of this page had the following objectives : (1) to perform a systematic review of the published literature to determine the overall rates of problems, complications, reoperations, and revisions after RSA; (2) to compare their influence on the final functional outcome; and, (3) to analyze the different problems, complications, reoperations, and revisions based on the etiology of the RSA. In the remainder of this article, I provide a summary of the article’s findings.
On the basis of the January 2011 study, the global rates for problems, complications, reoperations, and revisions after RSA were 44%, 24%, 3.5%, and 10%, respectively. However, wide variations were noted among the studies and occurred for several possible reasons. The definition of a problem or complication differs significantly among the studies.Whereas some authors included and reported all intraoperative or postoperative problems and complications during revisions, others did not because they were related to the revision procedure itself and not to the RSA implantation. Also, some series included radiographic changes around the humeral or glenoid components as complications, whereas others considered these separately as radiographic findings.
The complication and reoperation rates were much higher after revision RSA than after primary RSA.
Scapular notching was by far the most frequently reported problem after RSA. It was present in almost 50% of all the Grammont prostheses in the series, which is similar to the published rates in the literature on scapular notching using this reverse shoulder design.
The relative medialization of the center of rotation in the Grammont design is thought to predispose to impingement of the humeral component against the scapular neck in adduction. A biomechanical study by Nyffeler et al showed that the most important factor in preventing notching is inferior placement of theglenosphere.
In contrast to the Grammont design, the Encore/DJO prosthesis features a lateralized center of rotation. This design seems to be effective in preventing notching, because no notching was observed in the Encore prostheses in this study.
In my experience (MMT) the DJO design improves rotational range of motion by minimizing impingement, not only in abduction, but throughout the rotational range.
Although he clinical significance of scapular notching is a matter of some controversy, some studies have implicated scapular notching as a cause of glenoid component loosening and as having a negative impact on clinical outcome scores. Lucent lines around the glenoid component, which was the most frequently documented postoperative problem, did not appear to have any clinical effect. To prevent lucent lines of the glenoid, the consensus in other studies is that that the central peg of the base plate is thought to be the critical point for glenoid component stability and should be fixed in native bone stock.
The lateralization of the center of rotation in the Encore shoulder system, compared with the Grammont shoulder system, theoretically increases the torque forces at the glenosphere-baseplate interface. This was thought to be the reason for the more frequently reported lucent lines and glenoid loosening (5.8% vs 2.5%) in this reverse shoulder system. Although the rate of aseptic glenoid loosening is not reported to be a major problem in the Grammont system(2.5%), it had been reported in up to 11.7% in the first generation Encore system, which is comparable to the loosening rate of anatomic shoulder prostheses.
Changes in design to the current Encore/DJO system, including the addition of locking screws and hydroxyapatite coating of the baseplate, seem to have decreased the risk of loosening: a subsequent study using only the updated system had only 1 case of loosening in 96 RSAs. To avoid loosening, every effort should be made to optimally fix the glenoid component onto good bone stock at the inferior border of the glenoid.
Postoperative instability subsequent to RSA was the most frequent complication, but it is difficult to analyze the causes because of the variability among the studies. Factors such as altered version of the humeral and glenoid components, ruptured, and fatty infiltrated subscapular muscle and the complete release of the subscapularis, including the inferior and middle glenohumeral ligaments at the glenoid insertion site, may
predispose to weakened anterior restraints in deltopectoral approaches. Therefore, the subscapularis seems to be of tremendous importance and should be repaired and protected whenever possible.
Another potential cause of instability is a loss of tension of the deltoid. This could be because of preexisting atrophy or insufficiency of the anterior part of the deltoid, or because of relative humeral shortening compared with the contralateral side. In cases of revision or fracture sequelae, intraoperative assessment of deltoid tension can be difficult (eg, general anesthesia, fibrosis, scar, and retraction of soft tissue), and preoperative templating of the humeral length is essential. In recurrent instability, additional humeral spacers can be implanted with success.
In my experience (MMT), though repair of the subscpularis is performed, stability is much more related to proper version and soft tissue balancing. The DJO prosthesis has a more anatomic varus neck shaft angle, thus allowing more tensioning of the deltoid with increase cup size. This contrasts with the valgus angle of the Grammont design---in which increasing poly sizes increases tension by inferior displacement rather than lateral. Warner et al recently reported the risk of deltoid avulsion as a complication of previous open cuff repair in patients undergoing RSA with the Grammont design.
Postoperative infection rates were high both in primary and revision surgery. There was a trend toward higher infection rates in revision surgery compared with primary arthroplasty groups. The large subacromial dead space, the compromised general health of some patients, and the large surgical dissection, especially in revision cases, maypredispose to later infection.
Suffice it to say, however, that if one has a failed total or hemiarthroplasty, or a nonfunctioning rotator cuff, RSA or revision to RSA is a very good option. While long term follow-up is not yet available, improved designs and surgical technique are likely to improve survival rates.
The first series of reverse shoulder arthroplasty (RSA) with at least 2 years of follow-up confirmed the preliminary results, with excellent functional outcome and stable glenoid fixation. However, these series had a small numbers of patients and reported variable complication and revision rates of 15% to 50% and reoperation rates of 4% to 40%. One reason for the high variability was unclear definitions of complications and revisions, which varied markedly between the series.
A study attached at the bottom of this page had the following objectives : (1) to perform a systematic review of the published literature to determine the overall rates of problems, complications, reoperations, and revisions after RSA; (2) to compare their influence on the final functional outcome; and, (3) to analyze the different problems, complications, reoperations, and revisions based on the etiology of the RSA. In the remainder of this article, I provide a summary of the article’s findings.
On the basis of the January 2011 study, the global rates for problems, complications, reoperations, and revisions after RSA were 44%, 24%, 3.5%, and 10%, respectively. However, wide variations were noted among the studies and occurred for several possible reasons. The definition of a problem or complication differs significantly among the studies.Whereas some authors included and reported all intraoperative or postoperative problems and complications during revisions, others did not because they were related to the revision procedure itself and not to the RSA implantation. Also, some series included radiographic changes around the humeral or glenoid components as complications, whereas others considered these separately as radiographic findings.
The complication and reoperation rates were much higher after revision RSA than after primary RSA.
Scapular notching was by far the most frequently reported problem after RSA. It was present in almost 50% of all the Grammont prostheses in the series, which is similar to the published rates in the literature on scapular notching using this reverse shoulder design.
The relative medialization of the center of rotation in the Grammont design is thought to predispose to impingement of the humeral component against the scapular neck in adduction. A biomechanical study by Nyffeler et al showed that the most important factor in preventing notching is inferior placement of theglenosphere.
In contrast to the Grammont design, the Encore/DJO prosthesis features a lateralized center of rotation. This design seems to be effective in preventing notching, because no notching was observed in the Encore prostheses in this study.
In my experience (MMT) the DJO design improves rotational range of motion by minimizing impingement, not only in abduction, but throughout the rotational range.
Although he clinical significance of scapular notching is a matter of some controversy, some studies have implicated scapular notching as a cause of glenoid component loosening and as having a negative impact on clinical outcome scores. Lucent lines around the glenoid component, which was the most frequently documented postoperative problem, did not appear to have any clinical effect. To prevent lucent lines of the glenoid, the consensus in other studies is that that the central peg of the base plate is thought to be the critical point for glenoid component stability and should be fixed in native bone stock.
The lateralization of the center of rotation in the Encore shoulder system, compared with the Grammont shoulder system, theoretically increases the torque forces at the glenosphere-baseplate interface. This was thought to be the reason for the more frequently reported lucent lines and glenoid loosening (5.8% vs 2.5%) in this reverse shoulder system. Although the rate of aseptic glenoid loosening is not reported to be a major problem in the Grammont system(2.5%), it had been reported in up to 11.7% in the first generation Encore system, which is comparable to the loosening rate of anatomic shoulder prostheses.
Changes in design to the current Encore/DJO system, including the addition of locking screws and hydroxyapatite coating of the baseplate, seem to have decreased the risk of loosening: a subsequent study using only the updated system had only 1 case of loosening in 96 RSAs. To avoid loosening, every effort should be made to optimally fix the glenoid component onto good bone stock at the inferior border of the glenoid.
Postoperative instability subsequent to RSA was the most frequent complication, but it is difficult to analyze the causes because of the variability among the studies. Factors such as altered version of the humeral and glenoid components, ruptured, and fatty infiltrated subscapular muscle and the complete release of the subscapularis, including the inferior and middle glenohumeral ligaments at the glenoid insertion site, may
predispose to weakened anterior restraints in deltopectoral approaches. Therefore, the subscapularis seems to be of tremendous importance and should be repaired and protected whenever possible.
Another potential cause of instability is a loss of tension of the deltoid. This could be because of preexisting atrophy or insufficiency of the anterior part of the deltoid, or because of relative humeral shortening compared with the contralateral side. In cases of revision or fracture sequelae, intraoperative assessment of deltoid tension can be difficult (eg, general anesthesia, fibrosis, scar, and retraction of soft tissue), and preoperative templating of the humeral length is essential. In recurrent instability, additional humeral spacers can be implanted with success.
In my experience (MMT), though repair of the subscpularis is performed, stability is much more related to proper version and soft tissue balancing. The DJO prosthesis has a more anatomic varus neck shaft angle, thus allowing more tensioning of the deltoid with increase cup size. This contrasts with the valgus angle of the Grammont design---in which increasing poly sizes increases tension by inferior displacement rather than lateral. Warner et al recently reported the risk of deltoid avulsion as a complication of previous open cuff repair in patients undergoing RSA with the Grammont design.
Postoperative infection rates were high both in primary and revision surgery. There was a trend toward higher infection rates in revision surgery compared with primary arthroplasty groups. The large subacromial dead space, the compromised general health of some patients, and the large surgical dissection, especially in revision cases, maypredispose to later infection.
Suffice it to say, however, that if one has a failed total or hemiarthroplasty, or a nonfunctioning rotator cuff, RSA or revision to RSA is a very good option. While long term follow-up is not yet available, improved designs and surgical technique are likely to improve survival rates.
