Learning from baseplate failure in reverse total shoulder arthroplasty

 Baseplate failure is an important cause of failure of reverse total shoulder arthroplasty.

As these x-rays demonstrate, the reverse total shoulder is vulnerable because the baseplate has to resist the upward directed force applied by the humeral component on the glenosphere.

This load is resisted by (1) secure fixation of screws in good quality native glenoid bone (green arrows) and (2) compression of the superior aspect of the baseplate against prepared glenoid bone (yellow arrow).

In other words, good carpentry

the absence of which risks baseplate failure

A recent article from the American Shoulder and Elbow Surgeons,

Surgical and Patient Factors Associated with Baseplate Failures After Reverse Shoulder Arthroplasty: A Study by the ASES Complications of RSA Multicenter Research Group aimed to identify surgical, implant, and patient-related risk factors for baseplate failure after reverse total shoulder. 

Among 5,049 cases of rTSA followed for a minimum of 3 months, baseplate failure (defined radiographically as gross baseplate shift or hardware breakage) was identified in 83 (1.6%) cases at a median of 72 weeks post-surgery. These cases came from 40 centers performing large numbers of rTSAs, thus this rate is likely to substantially underestimate the actual rate of baseplate failure for all surgeons and patients. 

Because of the hardship experienced by patients with baseplate failure, we must learn from these cases how the risk of failure can be reduced: "what could the operating surgeon have done differently to avoid this complication?"

Most failures (76%) were atraumatic, suggesting either insecure initial fixation, lack of ingrowth or both. Radiographs showed hardware breakage in 68.7% of failures. Baseplate shift occurred in 78.3% of cases.  Revision arthroplasty had an odds ratio for baseplate failure of 4.57.

The actionable intelligence comes from the analysis of surgeon controlled variables: in primary rTSA, the risk of base plate failure was increased by the use of bone grafting (OR 4.42) and increased glenoid-sided lateral offset (OR 1.07). Central screw fixation (in contrast to use of peg or post) reduced failure risk (OR 0.55). In revision rTSA, only bone grafting remained significant (OR 3.75). Allograft use led to higher failure rates than autograft (14.7% vs. 3.9%).

Comment: In each case of reverse total shoulder arthroplasty there is an interplay between the quantity, quality and shape of native glenoid bone, the implants to be used and the experience and expertise of the surgeon. 

Each surgeon needs to answer key questions for each case: In my hands, can reaming of the available native bone provide sufficient screw fixation and backside support for baseplate stability and ingrowth? Will the use of augmented components improve baseplate fixation? In which cases is structural grafting needed to manage large uncontained bone loss?

When a patient experiences baseplate failure, the surgeon must ask, "what could I have done differently to avoid this failure. Each failure needs to inform that surgeon's management of future cases.

The Surgeon is the Method

Osprey using experience and expertise

Seattle

UW Campus

2024

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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).

Reverse total shoulder for severe glenoid defects.

 As emphasized by the authors of Functional and Radiographic Outcomes of Bone Grafting for Severe Glenoid Defects in Reverse Shoulder Arthroplasty, reverse total shoulder arthroplasty is commonly used to manage shoulders with major glenoid defects from either primary arthritis or from revision arthroplasty. One approach to these defects is using bone graft to fill in the defect . 

They report their outcomes for 20  primary arthroplasties

and 17 revision arthroplasties

 in which bone autograft (humeral head) or allograft (femoral head) was used to fill the defect prior to inserting a baseplate with a long central post.

Most primary arthroplasties had autografting while all revisions had allografting.

Of the 8 cases of baseplate failure (22% of the 37) at five years after surgery.

    8 had a Charleson Comorbidity Index of 3 or less (i.e they were pretty healthy)

    7 were in males    

    7 were in revision cases

    7 were in cases were allograft was used

    7 had graft resorption on the final radiograph    

    6 had gross shift of the baseplate on final radiograph

The authors noted that in contrast to the autograft cases, a substantial number of the allograft cases failed more than two years after arthroplasty, suggesting that lack of healing or resorption of the graft may be causative.

Comment: This report suggests that when using a baseplate with a long central post in healthy male patients having revision arthroplasty,  the use allograft may increase the rate of baseplate failure in the intermediate term. It seems possible that using a baseplate with a central compressive screw might yield better outcomes in these high risk cases, but this has not been rigorously established. Other alternative approaches might include augmented or custom baseplates. 

Getting durable purchase seems important for getting the job done

Lewis's Woodpecker

Oak Creek Wildlife Area

Washington 

2020

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
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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).

Augmented glenoid baseplates - the challenge of seating

Failure of the glenoid baseplate is an important complication of reverse total shoulder arthroplasty (see link and link).

At least two factors are important in minimizing this risk: (1) screw fixation in quality bone and (2) seating of the baseplate on the prepared glenoid.

Excellent seating is achieved when the glenoid is reamed to a single concavity and fit precisely with a convex backed baseplate resulting in full contact. 

In cases where the glenoid is biconcave or posteriorly or superiorly deficient to the extent that it cannot be safely reamed to a single concavity, 

the surgeon may elect an augmented baseplate.  

Partial and full augments are available.

Preparing the glenoid bone for an augmented component is more complex than for a baseplate with a single backside convexity.

Fitting the augmented component to the prepared bone is also more complex. See Rocking Horse Loosening of the Baseplate in Reverse Total Shoulder Arthroplasty.

 The preparation may require two different reaming steps 

And then positioning the baseplate to exactly fit the the prepared glenoid.

A recent article examined the Effects of implant rotational malposition on contact surface area after implantation of the augmented glenoid baseplate in the setting of glenoid bone loss

The authors point out that the backside of the augmented glenoid baseplate is not perpendicular to the axis of the central post/screw. Thus, if the baseplate is implanted with any rotational malposition, this could affect the backside contact area with loss of stability and the potential for bony ingrowth. 

They assessed the effect of rotational malpositioning of a full-wedge augmented on glenoid implant backside contact area using synthetic scapulas and a 15° full-wedge glenoid baseplate. 

The contact pressure between the baseplate and the glenoid surface at rotational positions 5°, 10°, and 15° clockwise (CW) and counterclockwise (CCW) from the central axis was measured with Extreme Low Fujifilm Prescale (Tekscan).

Gross contact was evaluated with a computed tomography scan.

The average contact area at zero degrees of malrotation was 37%. The average contact areas for the simulated malposition cases were

14% at 15° CCW,
25% at 10° CW,
19% at 15° CW.

On computed tomography, at 15° CCW, the contact area decreased by 39%; at 15° CW, the contact area decreased by 38%.

CT scans and Fujifilm pressure contact film for baseplates implanted at 0°, 10°, and 15° clockwise demonstrating decreasing amounts of surface contact between the baseplate backside and the glenoid surface with increasing rotational malposition

Comment: Awareness of the challenges of preparing for and fitting of an augmented glenoids should minimize the risk of failure of these components.

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). 

Reverse total shoulder - the complication of baseplate failure

Here are some cases of failure of the baseplate fixation to the scapula in reverse total shoulders performed with several different modern prosthesis systems. What do these failures have in common?

The answer, of course, is that in each case the glenosphere has been rocked up superiorly. This is because the major loads on the glenoid component - whether from deltoid contraction, from a fall, or from pushing up from the bed -  exert a superiorly directed force on the glenosphere that challenges the base plate's fixation to bone.

The ability of the glenoid component to resist these major loads depends on (1) secure bony fixation of the inferior screws in bone (green arrows) to resist failure in traction and (2) compression of the superior aspect of the baseplate against glenoid bone (yellow arrow) to prevent its rocking upwards as pointed out in Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis. 

If either of these is insecure, upward loads on the glenosphere can cause the baseplate to rock upwards away from the bone.

It's all about good carpentry: (1) preparing the glenoid bone so that there is maximal contact between the superior baseplate and host bone and (2) secure screw placement in good quality bone. If the quality of the bone suboptimal, insertion of the baseplate central screw without tapping may provide better fixation (see Avoiding Glenoid Baseplate Fixation Failure by Altering Surgical Technique for Varying Bone Densities). 

Bone graft may not be a perfect substitute for host bone; see Early radiographic failure of reverse total shoulder arthroplasty with structural bone graft for glenoid bone loss

The authors of How to Avoid Baseplate Failure: The Effect of Compression and RSA Baseplate Design on Implant Stability recognize that immediate, secure fixation of the baseplate is essential: patients may fall or otherwise load the glenosphere soon after surgery - long before any ingrowth has taken place. Furthermore, high compression of the central screw dramatically improves the initial (T=0) stability of the baseplate.

In Revision Reverse Shoulder Arthroplasty for the Management of Baseplate Failure: An Analysis of 676 Revision RSA Procedures the importance of maximizing the contact between the baseplate and supporting bone is again emphasized for both primary and revision reverse total shoulders.

Finally, the stability of the baseplate on the bone of the glenoid is optimized by inferior inclination of the glenosphere, which results in a compressive force on the baseplate against bone when the glenoid is loaded by the humerus (note the obtuse angle between the arrows)

 

...as opposed to the distracting force that results when the glenosphere is superiorly inclined  (note the acute angle between the arrows). (see Biomechanical comparison of component position and hardware failure in the reverse shoulder prosthesis)

It's about good carpentry

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).

Reverse total shoulder - baseplate screw failure

A woman in her late 50s had shoulder pain and weakness of her left shoulder after a failed cuff repair.

She desired a reverse total shoulder. At surgery there was an intact subscapularis but absent supraspinatus and infraspinatus.

Her sequential Grashey views are shown here

1.4 months post op

3 months post op

5.9 months post op. At this time she complained of some left shoulder pain after lifting her grandchild.

7.4 months post op. The left shoulder pain remained.

33 months post op The left shoulder pain abruptly increased.

Comment: The post operative views suggest incomplete seating of the base plate, which may have subjected the screws to bending forces leading to their failure from fatigue.

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To see our technique for reverse total shoulder, click on this link.

To support our research to improve outcomes for patients with shoulder problems, click here.

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How you can support research in shoulder surgery Click on this link.

To see our new series of youtube videos on important shoulder surgeries and how they are done, click here.

Be sure to visit "Ream and Run - the state of the art"  regarding this radically conservative approach to shoulder arthritis at this link and this link. Also see the essentials of the ream and run.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages   arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery 

The superior baseplate screw in reverse total shoulder arthroplasty: the least important and the most dangerous

Risk of Suprascapular Nerve injury during Glenoid Baseplate fixation for Reverse Total Shoulder Arthroplasty; A Cadaveric Study.

During implantation of the glenoid baseplate, screws are inserted through the glenoid face into the scapular body to achieve adequate fixation. Placement of peripheral baseplate screws in the superior and posterior glenoid may increase the risk of injury to the suprascapular nerve (SSN). These authors used a cadaveric model to evaluate the risk of SNN injury with placement of baseplate screws in the superior and posterior direction.

A bicortical 44 mm screw was placed in both the superior and posterior glenoid baseplate screw holes. Following implantation, the SNN was dissected and visualized through a posterior shoulder approach. The distance from the tip of the screws to the SSN and the distance from the screw’s scapular exiting hole to the SSN was recorded.

The superior screw contacted the SSN in 8 of the 12 specimens (66%). For the superior screw, the average distance from the exiting point in the scapula to the SSN was 9.2 ± 6.3mm with the shortest distance being 3.9 mm. The posterior screw contacted the SSN in 6 of 12 specimens (50%). For the posterior screw, the average distance from the exiting point to the SSN was 8.9 ± 3.8 mm with the shortest distance to the nerve being 2.2 mm.

Comment: While being the screw most likely to risk the supra scapular nerve and while being the screw most likely to predispose the scapular spine to fracture, the superior baseplate may be the least important screw for baseplate stability as shown below.

Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis

The baseplate of the reverse total shoulder usually fails from superiorly directed loads

Using an in vitro model these authors examined some of the factors affecting the quality of glenoid screw fixation, including the density of the material into which the screws are placed, the purchase of individual screws, and the direction of loading in relation to screw placement.

They found that 

(1) Load to failure was less when the glenoid component was fixed to material of lesser density. 

(2) While each screw contributed to the quality of fixation; the screw nearest the point of load application made the largest contribution. 

(3) Load to failure was less when the load was colinear with a line through the nonlocking holes in the base plate compared to colinear with a line through the locking holes. 

(4) For the most important direction of loading - a superiorly directed force applied to the glenosphere - the inferior screw appeared to be the most critical.

As shown in the diagram below, superiorly directed loads applied to the glenosphere by the humeral component (black arrow) subject the critical inferior screw to traction (red arrow), while the bone at the superior aspect of the glenoid (represented by the grey box) is subjected to compression (green arrow) - which results in minimal loading of the superior screw.

For these reasons we prefer to shorten the drill hole and the screw used in the superior hole of the baseplate and work to assure good bony support for the superior aspect of the baseplate.

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To see a YouTube of our technique for a reverse total shoulder arthroplasty, click on this link.

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To see our new series of youtube videos on important shoulder surgeries and how they are done, click here.

Use the "Search" box to the right to find other topics of interest to you.

How you can support progress in shoulder surgery

You may be interested in some of our most visited web pages  arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'