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

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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).

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

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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). 

Avoiding baseplate screw failure in reverse total shoulder arthroplasty - innovation without increased cost or complexity

In followup to our post Reverse baseplate failure - fracture of the central screw, the senior author of Avoiding Glenoid Baseplate Fixation Failure by Altering Surgical Technique for Varying Bone Densities offered that "one technical issue leading to incomplete seating is very dense subchondral bone which can provide false sense of the implant being fully seated; another pitiful is if there is some cartilage left on the glenoid which also can lead to incomplete seating booth of these have happened with screw breakage at the interface of the baseplate screw junction"

His conclusions can be summarized as follows:

(1) baseplate failure is an import complication of reverse total shoulder arthroplasty

(2) time zero (immediate post op) stability of the baseplate is important because (a) the patient will load the baseplate before any bone ingrowth has had time to occur and (b) micro motion of the baseplate will inhibit bone ingrowth so that the screws may be all that is holding the baseplate to the glenoid bone leading to the risk of fatigue fracture

(3) failure to remove cartilage and interposed tissue between baseplate and bone may prevent adequate seating of the baseplate

(4) as is the case with all screw fixation in bone, bone quality has a strong effect on the quality of fixation: (a) low bone density may result in lack of a solid "bite" (screw stripping); (b) high bone density may result in incomplete seating

(5) from plain radiographs, the surgeon can preoperatively get an idea of the glenoid bone density: poor (below left), sclerotic (below right).

(6) for bone suspected of having poor bone quality, the author uses some straightforward innovations that do not add time, technology or expense: 

    (a) for soft bone the glenoid is reamed over a 2.5 mm drill (without using a tap) followed by insertion of the baseplate in the untapped bone 

    (b) for denser than average bone,  a 3.0-mm drill is used for the pilot hole, and then the tap is passed (inserted and removed) a total of 3 times, followed by insertion of the baseplate in the tapped bone 

    (c) the standard technique is used for average density bone: a 2.5-mm drill is inserted in the central hole to a depth of 30 mm, followed by use of the 6.5-mm tap, reaming of the glenoid, and finally, insertion of the monoblock baseplate

In in vitro testing using a low-density block model, the standard technique gave a compressive force of 112 N compared with 300 N for the soft bone technique.

In the high-density bone model, the standard technique resulted in failure to seat the baseplate, or screw breakage. Performing the dense bone technique, the baseplate was seated without failure, with an average compressive force of 450 N. 

Comment: Time zero (initial) fixation is important for minimizing the risk of baseplate failure. This requires adequate bone preparation for maximal baseplate-bone contact, full seating of the baseplate and placement of the peripheral screws in good quality bone.

The inspection of preoperative plain radiographs and the use of the techniques suggested here can reduce the risk of inadequate compression on one hand and incomplete seating on the other. 

It is noted that with this implant system, the only screw providing substantial compression is the central one - the others are locking screws. 

Finally, in cases where the central screw is stripped, we have found that "match stick" strips of cortical bone can be progressively added to the central hole until good compression is achieved.

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). 

  

Rocking horse loosening of the baseplate in reverse total shoulder arthroplasty.

One of the most common modes of baseplate failure in reverse total shoulder (RSA) is rocking horse loosening resulting from the inability of the fixation to resist upward directed force applied by the humerus. 

 As pointed out in Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis, the ability of the baseplate to resist the rocking (green arrow) from superiorly directed loading (black arrow) depends in large part on (1) compression of the upper aspect of the baseplate against bone of good quality (yellow arrow) and (2) the pullout resistance of the most inferior screw (red arrow). 

As pointed out in Clinical and radiological outcomes with an augmented baseplate for superior glenoid wear in reverse shoulder arthroplasty patients having RSA not infrequently have superior glenoid erosion.

which can be managed by orienting the reamer to preserve the important superior glenoid bone, achieving the desired inferior tilt, and then using a standard glenoid component.

or by reaming along a neutral glenoid axis, sacrificing superior bone, and using an augmented glenoid component to achieve the desired tilt.

A risk with the latter approach is (1) inadequate seating of the baseplate against superior glenoid bone (red arrow) and (2) lack of secure screw fixation in the inferior glenoid bone (red oval). 

The authors of the study referenced above aimed to assess the impact of using the metal-augmented glenoid baseplate (AGB) on improving clinical and radiological outcomes, as well as reducing complications, in patients with superior glenoid wear undergoing reverse shoulder arthroplasty (RSA). 24 such patients were propensity matched to 72 patients who received a standard glenoid baseplate (STB) after eccentric reaming (Group B). At 2 year followup patients in both groups were improved with respect to patient reported outcomes, but AGB showed no additional benefit. 

Group A experienced more acromial stress fractures (3 cases; 12.5%), whereas Group B had a higher occurrence of scapular notching (24 cases; 33.3%).

Early clinical and radiographic outcomes of an augmented baseplate in reverse shoulder arthroplasty for glenohumeral arthritis with glenoid deformity also noted a high incidence of acromial stress fractures with augmented glenoid components: Acromial stress fractures developed in 11.4% of the patients.

Comment: The value to the patient of the more expensive augmented baseplate was not demonstrated in this manuscript.

No baseplate failure was noted in this two year followup study. 

Nevertheless the article provides an opportunity to consider the factors that may increase the risk of rocking horse loosening of the glenoid component in reverse total shoulder. 

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

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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).

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'

Is intraoperative navigation of value for baseplate fixation of the Equinoxe Reverse Total Shoulder?

Role of intraoperative navigation in the fixation of the glenoid component in reverse total shoulder arthroplasty: a clinical case-control study

These authors point out that fixation of the glenoid baseplate in reverse total shoulder arthroplasty (rTSA) is an important factor in the success of the procedure. They state that although aseptic loosening comprises 1.1%to 5% of the postoperative complications for rTSA it accounts for 18.2% of revisions.

They sought to determine whether computed tomography–based computer navigation improved the glenoid base plate fixation of the Exactech baseplate that uses an ingrowth central peg and angled peripheral screws.

Patients undergoing rTSAs using navigation (NAV, N = 27) and manual technique (MAN, N= 23) from January 2014 to July 2017 were analyzed in a case-control design. Screw purchase length and central cage perforation were assessed using multiplanar computed tomography. Central cage perforation was defined as a breach in the scapular wall in any plane.

Median screw purchase length was significantly longer in the NAV group for both anterior (20 mm vs. 15 mm, P <.01) and posterior screws (20 mm vs. 13 mm, P <.01), but not for the superior and inferior screws.

The NAV group displayed significantly reduced incidence of central cage perforation (17.7% vs. 52.4%, P . .04).

The authors concluded that for the Exactech baseplate, the use of computer-assisted navigated rTSA contributes to significant alterations in screw purchase length, screw angulation, and central cage perforation of the glenoid baseplate compared with non-navigated methods.

Comment: This is an interesting retrospective investigation that applies specifically to the prosthesis system studied. Some additional data would be helpful in assessing the value of the "NAV" system: (1) what is the incremental cost of implementing and using the NAV?, (2) has it been demonstrated that even a small amount of scapular penetration by the central peg affects the stability of the Equinoxe baseplate?, (3) how much is the fixation of the baseplate compromised by the observed changes in screw length and angulation" (4) are the clinical results different for those shoulders in which NAV is used?

For this prosthesis, restricting micromotion between the base plate and the underlying bone to below 150 micrometers is considered ideal for encouraging bony ingrowth. For other systems that do not require bone ingrowth and that have different methods for fixation (such as that shown below) the case for navigation may be less compelling.

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We have a new set of shoulder youtubes about the shoulder, check them out at this link.

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

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'