Shoulder Arthroplasty Failure Research in action

Most patients having primary arthroplasty do well, 

thus we learn most from studying the failures.

Publications of shoulder arthroplasty outcomes usually report the diagnostic categories associated with failure, such as glenoid component loosening, rotator cuff tear, infection, or instability. While such classifications are descriptively useful, they provide little insight into how failures might be prevented for future patients.

As Judea Pearl has emphasized in his must-read book

actionable knowledge is more likely to arise from asking the counterfactual question: “What might have been done differently that could have prevented this complication?” This principle underlies the Shoulder Arthroplasty Failure Research initiative, which seeks to move beyond descriptive epidemiology toward identification of surgeon-controlled, modifiable factors that govern arthroplasty failure.

A recent study exemplifies this approach: “Humeral and glenoid component malposition in patients requiring revision shoulder arthroplasty: a retrospective, cross-sectional study.” In this investigation, failure of a primary arthroplasty was defined as the occurrence of revision. The authors reviewed 234 revision shoulder arthroplasties performed at 3 institutions.

They reported demographic characteristics and frequencies of revision types following hemiarthroplasty, anatomic total shoulder arthroplasty (TSA), and reverse total shoulder arthroplasty (RSA)

While such descriptive information is important, it does not inform strategies for prevention of arthroplasty failure for patients having arthroplasty in the future. 

The study focused on some of the factors under the surgeon’s control, specifically the position of glenoid and humeral components. The findings were striking: glenoid malposition was identified in 51% of anatomic TSA revisions and 93% of RSA revisions. Humeral component malposition was also frequent, present in 57% of anatomic TSA, 62% of RSA, and 54% of hemiarthroplasty cases. These observations support the counterfactual inference that had the components been positioned appropriately, the likelihood of failure requiring revision may well have been substantially reduced. 

Here are a few examples from the article.

Placement of the RSA baseplate in superior tilt.

Superior placement of the RSA baseplate.

Superior placement of the humeral component in anatomic TSA

Inadequate humeral neck cut in hemiarthoplasty resulting in

superior-medial placement of the humeral component and overstuffing of the joint.

In that the surgeon is the method, each of these malpositions could have been avoided by better surgical technique.  The institutions conducting the revisions were usually not involved in the majority of the primary procedures and thus medical records for many of these patients could not be fully reviewed. As a result, the characteristics of the surgeon performing the primary arthroplasty that was revised (age, training, years in practice, arthroplasty experience, etc) were not available, but would be of great interest.

Comment: This is an imporant study in that it identifies actions that shoulder surgeons can take to reduce the risk of arthroplasty failure for their future patients. It provides a model of how clinically meaningful shoulder arthroplasty failure research can be conducted.

This is an uncommon bird, but well worth investigating.

Elegant Trogan

Madera Canyon, Tucson AZ

May, 2022

Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link)
Shoulder rehabilitation exercises (see this link).

Dislocation of the reverse total shoulder

Instability and dislocation are major complications of reverse total shoulder arthroplasty (RSA) and are not easily solved by revision.

To help understand reverse shoulder stability and instability I will use some diagrams by Steve Lippitt from the 5th Edition of Rockwood and Matsens' The Shoulder (note that the completely revised 7th edition will be published next year - wait for it!).  Steve was also critical to the understanding of concavity compression and describing the stability ratio (which will be discussed later in this post). See Glenohumeral stability from concavity-compression: A quantitative analysis

The reverse total shoulder is stabilized by conconcavity compression in which the concavity of the humeral polyethylene is pressed onto the glenosphere by the vector sum of muscle action, gravity and other forces (red arrow).

Dislocation can result when the compressive forces or the concavity of the humeral cup are insufficient to manage a displacing load, such as that from pushing one's self up from an armchair. 

Dislocation can result when the vector sum of the forces acting on the humerus is not aligned with the glenosphere,

When unwanted contact occurs between the scapula and humeral component, displacing forces can misalign the compressive force required for stability.

To start, I'd like to direct the reader to several classic articles on this topic: 

2011 Complications in reverse total shoulder arthroplasty

2015 Results of closed management of acute dislocation after reverse shoulder arthroplasty

2016 Revision for a failed reverse: a 12-year review of a lateralized implant

2018 Classification of instability after reverse shoulder arthroplasty guides surgical management and outcomes

2023 Revision for instability following reverse total shoulder arthroplasty: outcomes and risk factors for failure

I'll pick up the story from 2024 to the time of this writing (April 2025).

*Dislocation of the reverse total shoulder continues to be a major and prevalent issue for patients and surgeons

Mitigating the Risk of Instability After Reverse Shoulder Arthroplasty: A Critical Analysis Review of Patient and Surgical Factors  Instability and dislocation after reverse shoulder arthroplasty may occur in up to 31% of patients. Clinical risk factors for instability include younger age, male sex, increased body mass index, preoperative diagnosis of proximal humerus fracture or rotator cuff pathology, history of instability of the native shoulder or after surgery, and a medical history of Parkinson's disease. In patients at a high risk of instability, surgeons should consider a more lateralized prosthesis (particularly in patients with an incompetent rotator cuff), repairing the subscapularis (particularly when using a medialized prosthesis), and upsizing the glenosphere (>40 mm in male and 38-40 mm in female patients). While potentially useful, less evidence exists for the use of a constrained liner.

Midterm outcomes of primary reverse shoulder arthroplasty: a systematic review of studies with minimum 5-year follow-up The rate of shoulder dislocation was 3.7% (0%-20.4%),

Instability after reverse shoulder arthroplasty: a retrospective review of thirty one cases The most frequent etiology for RSA instability was loss of compression, followed by impingement and loss containment.

Revision of reverse total shoulder arthroplasty: A scoping review of indications for revision, and revision outcomes, complications, and re-revisions 22% of the complications were dislocations or instability. 30% of the revisions were for dislocation or instability.

Predictors of dislocations after reverse shoulder arthroplasty: a study by the ASES complications of RSA multicenter research group.  Patients with a primary diagnosis of glenohumeral osteoarthritis with an intact rotator cuff had an overall lower rate of dislocation than patients with other diagnoses (0.8% vs. 2.5%. Patient-related factors independently predictive of dislocation, in order of the magnitude of effect, were a history of postoperative subluxations before radiographically confirmed dislocation (odds ratio [OR]: 19.52), primary diagnosis of fracture nonunion (OR: 6.53), revision arthroplasty (OR: 5.61), primary diagnosis of rotator cuff disease (OR: 2.64), male sex (OR: 2.21), and no subscapularis repair at surgery (OR: 1.95). 

Complications following reverse total shoulder arthroplasty for proximal humeral fractures: a systematic review The most common postoperative complication was prosthetic instability/dislocation: 2.3%

Complications after reverse shoulder arthroplasty for proximal humerus nonunion The most common postoperative complication was prosthetic instability/dislocation: 12%

Poor clinical outcomes and high rates of dislocation after modular reverse shoulder arthroplasty for proximal humeral oncologic resection Dislocations occurred in 40%

Intraoperative repair of functional subscapularis during RSA by deltopectoral approach could improve internal rotation but does not prevent anterior dislocation. In the functional repair group, three shoulders (1.2%) reported subjective instability and 1 (0.4%) dislocated.None occurred in in either the non-functional repair or non-repair groups. 

Reverse shoulder arthroplasty with a 155 degrees neck-shaft angle inlay implant design without reattachment of the subscapularis tendon results in satisfactory functional internal rotation and no instability: a cohort study. One out of 210 prostheses was revised for dislocation within the first month after primary surgery.

Impact of morbid obesity on postoperative outcomes in reverse total shoulder arthroplasty: A national inpatient sample analysis Morbid obesity (BMI >/=40 kg/m(2)) was associated with a periprosthetic dislocation rate of 2.60 % in comparison to 1.59 % in controls

Impact of accumulating risk factors on the incidence of dislocation after primary reverse total shoulder arthroplasty using a medial glenoid-lateral humerus onlay prosthesis. 1.4% of the patients experienced dislocation with a medialized glenoid-lateralized humerus onlay rTSA prosthesis. The greatest risk factors for dislocation were male sex, age <68 years at the time of surgery, patients with body mass index >30, patients who received glenospheres having a diameter >40 mm, and patients who received expanded or laterally offset glenospheres.

Low success rate of closed reductions when treating dislocations after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group.  a closed reduction was initially attempted in the majority of patients, but only about one-third were successful and required no further intervention. Unsuccessful closed reductions were associated with higher patient BMI. Revision surgery for dislocations was complicated by a high rate of recurrent dislocations and rerevision surgery.

*The diameter, depth and orientation of the humeral cup affect stability of the reverse total shoulder. However, it must be remembered that the ability of the RSA to resist dislocation depends not only on the shape and orientation of the cup, but also on the direction and magnitude of the net force as shown by the red arrows in the first two diagrams at the start of this post.

From Grammont to a New 135 degrees Short-Stem Design: Two-Hand Lever Test and Early Superior-Lateral Dislocations Reveal Critical Role of Liner Stability Ratio and Stem Alignment

.

Illustration of a reverse total shoulder arthroplasty: radius (r) of the glenosphere and concavity depth (d) or jump height of the liner are required to calculate the liner stability ratio (LSR). Yellow area: the extent of the glenosphere covered by the liner; yellow striped line: angle of coverage (degree of glenosphere coverage by the liner).

Patients having receiving RSA had an 8% dislocation rate for standard liners and a 0% dislocation rate for retentive liners. The authors attribute this difference to the jump height for the 36 mm standard implant of 8.1 and a linear stability ratio (LSR) of 152%; whereas the 36 mm retentive liner had a jump height of 10.1 and linear stability ratio of 195 to 202%

For this design, the most stable liner type was the 36 retentive:

They also found that the mean effective neck-shaft angle was 133 degrees (127-144 degrees) for short stems and 135 degrees (129-143 degrees) for long stems. Long stems significantly reduced varus outliers

which may have an increased risk for instability.

Varus-valgus alignment of humeral short stem in reverse total shoulder arthroplasty: does it really matter? The utilization of short humeral stems in reverse total shoulder arthroplasty has gained attention, however, concerns exist regarding the risk of misalignment with implant insertion. In this cadaver study, anterior dislocation forces were considerably lower in the varus group compared to the neutral group.  Valgus positioning did not significantly impact instability compared to the neutral position.

*Know the implants you're using

Large variability in degree of constraint of reverse total shoulder arthroplasty liners between different implant systems There were variations in jump height between rTSA systems at a given size, resulting in large differences in stability ratio. Standard liners exhibited a stability ratio range from 126% to 214% (mean 158% (SD 23%)) and constrained liners a range from 151% to 479% (mean 245% (SD 76%)). The angle of coverage showed a range from 103 degrees to 130 degrees (mean 115 degrees (SD 7 degrees) for standard liners and a range from 113 degrees to 156 degrees (mean 133 degrees (SD 11 degrees )) for constrained liners.

Four arthroplasty systems had constant stability ratios for standard liners (within 5%) across different sizes, while one system showed slight inconsistencies (within 10%), and ten arthroplasty systems showed large inconsistencies (range 11% to 28%). The stability ratio of constrained liners was consistent across different sizes in two arthroplasty systems and inconsistent in seven systems (range 18% to 106%). 

Impact of constrained humeral liner on impingement-free range of motion and impingement type in reverse shoulder arthroplasty using a computer simulation The humeral liner may be changed to a constrained type when stability does not improve by increasing glenosphere size or lateralization with implants, and patients, particularly women with obesity, have risks of periprosthetic instability that may be secondary to hinge adduction on the thorax. This RSA computer simulation model demonstrated that constrained humeral liners led to decreased impingement-free ROM. 

From Dr Stefan Bauer I received the most interesting response below.

 

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link

Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link)
Shoulder rehabilitation exercises (see this link).

Reverse total shoulder complication - fracture of central baseplate screw

Baseplate failure is a serious complication of reverse total shoulder arthroplasty. See Reverse total shoulder, the complication of baseplate failure.

Here's an example case. An active man had multiple prior attempts at rotator cuff repair, but eventually developed cuff tear arthropathy. 

This was treated with a reverse total shoulder arthroplasty (RSA).

Of note, the baseplate is not in contact with the genoid bone superiorly (see gap at arrow)

The patient returned to physical activity including pushups. A year after the RSA, the shoulder became painful on use. X-rays showed superior tilting of the glenosphere and bending of the central screw.

Eventually the central screw fractured and the glenosphere fixation failed.

Here is an example of fatigue fracture of the central screw.

This case exemplifies the points made by the authors of 

Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis, specifically that the security of baseplate fixation depends in large part on (1) supporting contact between the upper aspect of the baseplate and glenoid bone and (2) strong fixation of the inferior screw in good glenoid bone.

When such support is lacking, there is a risk of fatigue fracture of fixation screws and baseplate loosening.

Loss of superior support for the baseplate can occur when the glenosphere is inferiorly inclined. In other words, inferior inclination requires substantial glenoid reaming to achieve support for the superior baseplate.

Some related articles are referenced below.

How to avoid baseplate failure: the effect of compression and reverse shoulder arthroplasty baseplate design on implant stability

Avoiding Glenoid Baseplate Fixation Failure by Altering Surgical Technique for Varying Bone Densities

Reverse shoulder glenoid loosening: an evaluation of the initial fixation associated with six different reverse shoulder designs

Comment: We invited a very experienced RSA surgeon to give us his perspective. He kindly responded "I too have this failure mode but i think it relates to imperfect seating.  

If there is no bony contact of the baseplate inferiorly that leads to lack of ingrowth. There is a small gap inferiorly too of the baseplate. 

The lack of ingrowth is why the screws failed at the interface to the screw/baseplate junction. I have not had failures with lack of superior contact 

if there is inferior  contact."

Comments welcome at shoulderarthritis@uw.edu

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link


Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/


Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).

Shoulder rehabilitation exercises (see this link). 

Salvaging the failed humeral arthroplasty with humeral bone loss.

Proximal humerus bone loss is commonly encountered in revision shoulder arthroplasty. Bone loss can occur from component loosening and ensuing osteolysis, infection, as well as preoperative and intraoperative fracture. Careful preoperative assessment of the humeral anatomy can inform planning for surgical revision. Of particular importance is the quantity and quality of bone along the humeral diaphysis and metaphysis and the condition of the important soft tissue attachments, including the rotator cuff, deltoid and pectoralis major.

Humeral bone deficiencies can contribute both to instability of the joint and to instability of fixation of the revision implant.



1. Joint instability

The stability of the reverse total shoulder depends on concavity compression: the compression of the glenosphere into the concavity of the humeral liner by the deltoid and other scapulohumeral muscles.

Post-revision glenohumeral instability of the reverse total shoulder can be caused by inadequate restoration of humeral length and/or soft tissue attachments to the proximal humerus. Loss of humeral length reduces the tension in the deltoid, and thereby decreases its ability to provide the compressive force that stabilizes the joint. Compromised insertions of subscapularis, coracobrachialis, latissimus dorsi / teres major and pectoralis major can also contribute to insufficient joint compression.

2. Implant instability.

Instability of the humeral component is often manifested by inadequate rotational stability of the implant in the humerus. The non-circular cross section of the metaphyseal canal provides the best opportunity for obtaining rotational stability.

Some of the steps that are helpful in optimizing (1) the stability of the joint and (2) the stability of the humeral component in revision reverse total shoulder include

1. Assessing the quantity, quality and pathoanatomy at each level of the humeral bone.

Humeral Bone Loss in Revision Total Shoulder Arthroplasty: the Proximal Humeral Arthroplasty Revision Osseous Insufficiency (PHAROS) Classification System characterized the bone loss in three regions (epiphysis (1), metadiaphysis above the deltoid insertion (2), and diaphysis below the deltoid insertion (3)) as well as the bone quality in terms of cortical thinning of greater (A) or less than 50% (B) of the expected thickness. Epiphyseal bone loss can isolated compromise of the medial calcar (C) or greater tuberosity (G).



Some examples are shown below. The authors recommend that grade 2B and 3 bone loss be treated with allograft-prosthetic composites (APC) or a humeral replacement mega-prosthesis.




2) Determining whether residual cement is securely attached to bone and of possible use of cement-within-cement fixation of a new humeral implant

The example below shows an intact cement mantle without radiographic signs of loosening at the bone-cement interface. The revision was performed with a cement-in-cement revision and resulted in stable fixation at 4 years after surgery.




The example below shows a cement mantle fracture and radiolucency at the bone-cement interface that raises concern about the applicability of a cement-in-cement revision



3) Evaluation of the risk of infection (serum WBC, ESR, CRP, frozen sections, joint fluid for cell count, frozen sections, as well as submission of tissue explant specimens for culture). Often a course of postoperative antibiotics is used until the results of the intraoperative cultures become available. 

4) Restoring humeral length to optimize soft tissue tension 

One approach to restoring humeral length is to utilize contralateral films as guide to the desired humeral length as shown below.

Another approach is to determine the added length necessary to restore soft tissue tension as detailed by the authors of Revision Arthroplasty with Use of a Reverse Shoulder Prosthesis-Allograft Composite

5) Achieving secure fixation of the implant to healthy host bone, such as purchase in a length of healthy diaphysis exceeding two cortical diameters (see Evaluation and treatment of postoperative periprosthetic humeral fragility fractures)

6) Assuring robust rotational control of implant, for example through plate fixation of APC to host bone.

7) Retaining or restoring critical soft tissue attachments, such as deltoid, pectoralis major, remaining rotator cuff and subscapularis 

Example below from Ben Sharareh, past UW Shoulder Fellow

8) Minimizing stress risers at distal end of APC, especially in osteoporotic bone (avoid ending plate and stem at same level, “protecting the whole bone”). Example below from Jonah Hebert-Davies, UW Shoulder Faculty.

9) Optimizing stability of glenohumeral articulation (selection of glenosphere diameter of curvature and lateral offset, tensioning using polyethylene liner of appropriate thickness, avoiding unwanted contact between humerus and scapula (neck, acromion).

The example below shows a glenosphere exchange to a larger diameter, inferior offset at a revision for humeral loosening with massive humeral bone loss. The new glenosphere optimizes soft tissue tension and compression.

Below are some of the relevant articles on revision reverse total shoulder arthroplasty in shoulders with loss of humeral bone.

2009 Revision Arthroplasty with Use of a Reverse Shoulder Prosthesis-Allograft Composite recommended allograft-prosthesis composites in cases with humeral defects ranging from 3.5 to 15.0 cm.

2013 Revision surgery of reverse shoulder arthroplasty points to the association of bone loss with humeral loosening, lack of rotational stability, and infection.

2014 The metaphyseal bone defect predicts outcome in reverse shoulder arthroplasty for proximal humerus fracture sequelae found that the clinical outcome was influenced by a metaphyseal bone defect of more than 3 centimeters and degenerative changes of the teres minor. 

2016 Long-term analysis of revision reverse shoulder arthroplasty using cemented long stems  emphasized the importance of sufficient quantity and quality of distal humeral bone in obtaining fixation with long stem cemented humeral components.

2017 Large diaphyseal-incorporating allograft prosthetic composites: when, how, and why : Treatment of advanced proximal humeral bone loss  found that well-fixed humeral stems could be treated with short metaphyseal allografts in most cases. Loose stems required longer diaphyseal-incorporating allografts. Noncemented stems required diaphyseal grafts in most cases, compared to cemented stems which required larger grafts in one-third of cases.

2018 Humeral Bone Loss in Revision Shoulder Arthroplasty indicated proximal humeral allograft for revisions of shoulders with 5 cm or more proximal humeral bone loss). 

2019 Clinical outcomes following reverse shoulder arthroplasty-allograft composite for revision of failed arthroplasty associated with proximal humeral bone deficiency: 2- to 15-year follow-up." 

2019 Humeral Bone Loss in Revision Total Shoulder Arthroplasty: the Proximal Humeral Arthroplasty Revision Osseous Insufficiency (PHAROS) Classification System  divided bone loss into three regions (epiphysis, metadiaphysis above the deltoid insertion, and diaphysis below the deltoid insertion) and bone quality by cortical thinning of greater or less than 50% of the expected thickness. Epiphyseal bone loss is subdivided into isolated compromise of the medial calcar or greater tuberosity. The authors provided radiographic examples of each degree of bone loss.

2023 Humeral bone defects in revision shoulder arthroplasty  divided bone loss based on the involvement of five segments of the humerus, as shown below This classification helps accounts for loss of bone in regions of stabilizing muscle attachments.

This post was prepared with the great help and direction from Mihir Sheth, M.D., UW shoulder fellow.

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link.

Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).