Glenoid erosion in humeral hemiarthroplasty - how to minimize the risk

 Glenoid erosion is a recognized cause of inferior clinical results in humeral hemiarthroplasty.

While there is much current interest in the use of a pyrocarbon joint surface to reduce glenoid erosion, as the x-ray above demonstrates, glenoid erosion can take place with pyrocarbon as well as with metal humeral heads.

Here we present some approaches to reducing the risk of glenoid erosion that apply no matter what type of joint surface is used.

The gleonoid.

In the great majority of arthritic shoulders, there is loss of the congruency between the humeral and glenoid articular surfaces. Thus, rather than having the load distributed evenly across the joint (below left), the load is concentrated on a reduced area at the back of the joint. The resulting pressure (load/area) causes progressive posterior bone loss and decentering.

If a hemiarthroplasty is performed without addressing this force maldistribution, the posterior bone erosion will continue.

On the other hand, if conservative glenoid reaming is used to create a single concavity, even load distribution can be achieved. 

Experience suggests that a 2 mm diametral mismatch between the humeral head and the reamed glenoid is optimal.

If glenoid erosion is to be minimized, the maximum amount of the best quality bone (arrows) needs to be preserved.

by conservative reaming

This can be accomplished by accepting, rather than correcting, glenoid retroversion.

The diagrams below show the preservation of quality bone with accepting the glenoid retroversion (left) in comparison to the greater amount of bone removed with correcting glenoid retroversion (right)

In reaming the glenoid, sharp reamers and irrigation can help minimize the risk of thermal injury to the glenoid bone (see Thermal effects of glenoid reaming during shoulder arthroplasty in vivo).

While some surgeons advocate drilling holes in the reamed glenoid surface

it is apparent that this can weaken the glenoid surface making it more prone to erosion. Perhaps this "docking" is more appropriate when making a pie.

Finally, when possible it is desirable to preserve the glenoid labrum recognizing its load bearing and stabilization functions.

Overstuffing: Soft tissues

As pointed out in How to Overstuff an Anatomic Arthroplasty and Overstuffing is not a radiographic diagnosis, overstuffing is a condition in which the size and position of the shoulder arthroplasty implants result in excess tightening of the soft tissues encapsulating the joint. Thus, a shoulder with a chronically tight capsule and rotator cuff may be overstuffed by normally sized implant.

As pointed out in Practical Evaluation and Management of the Shoulder, overstuffing can not only restrict the range of glenohumeral motion

but it can also increase the force necessary to move the joint,
   

which increases pressure on the glenoid joint surface when vigorous stretching is carried out.

Thus for that reason, soft tissue releases are important for reducing the pressure on the glenoid and the risk of glenoid erosion. 

180 degree releases if there is excessive posterior translation

360 releases if the shoulder is tight all around

The adequacy of the releases can be verified while the trial components are in place, verifying that the shoulder can be easily flexed to at least 150 degrees

and that the shoulder meets the 40, 50, 60 rules (40 degrees of external rotation with the subscapularis approximated, 50% posterior translation, and 60 degrees of internal rotation with the arm abducted).

Overstuffing: Implant size and positioning.

While much attention is being paid to pyrocarbon as an alternative bearing surface, glenoid erosion can be seen with humeral heads of any type of material.

Common implant related causes of overstuffing.

(1) Inadequate head cut, leaving a too long neck.

(2) Too large humeral component

(3) Head too medial

(4) Head too high

When the head is high, it acts like a cam (click here), excessively tightening the inferior capsule when the arm is elevated because the center of rotation is malpositioned. This tightening results in increased pressure on the glenoid surface when the arm is raised.

(5)  Head high and medial

From the above it is noted that humeral head malposition can occur with pyrocarbon and with metal heads; humeral head malposition can occur with stemless, short stem and standard length stems.

To avoid overstuffing related to the humeral component, careful attention needs to be paid to the neck cut, head size and component position.

Conclusion

The risk of glenoid erosion can be reduced by preserving and protecting the best bone in the glenoid, balancing the soft tissues to optimize glenoid laxity, along with careful selection and positioning of the humeral component.

Avoiding glenoid erosion appears to depend more on surgical technique than on technology.

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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). 

Osteoarthritis: Hemiarthroplasty vs Total Shoulder. A pitfall of propensity score matched analysis

Randomization enables unbiased estimation of treatment effects; randomization attempts to assure that treatment-groups are balanced with respect to the important covariates. Unfortunately for us shoulder surgeons, surgical treatments are rarely assigned randomly.

Propensity matching is an attempt to use observational data to compare two treatment groups by accounting for the covariates that are associated with the outcome. 

The possibility of bias arises because a difference in the outcome between treatment groups may be caused by factors that predict which treatment the patient receives rather than the effectiveness of each treatment. For example if an observational study matching patients for age and sex alone retrospectively compared the recurrence rates after Bankart repair and after the Latarjet procedure, it would be at risk for an incorrect conclusion because it did not match for the size of the glenoid defect which may have affected the choice of treatment.

With that background let's look at Shoulder Hemiarthroplasty Is Associated With Higher 30-Day Complication Rates Compared With Total Shoulder Arthroplasty for Glenohumeral Osteoarthritis: A Propensity Score Matched Analysis. So, everyone with OA should get a TSA rather than an HA, right? 

However, the title itself gives pause: why should a smaller operation (hemiarthroplasty) have a higher short term postoperative complication rate than a more involved procedure (total shoulder arthroplasty)? Sounds like a fundamental attribution error.

Let's take a deeper dive. The authors searched the American College of Surgeons National Surgical Quality Improvement Program database for records of patients who underwent either TSA or HA for glenohumeral osteoarthritis of the glenohumeral joint. 

Patients in each group underwent a 1:1 propensity match for age, sex, BMI, ASA classification, diabetes mellitus, hypertension requiring medication, congestive heart failure, chronic obstructive pulmonary disease, inpatient/outpatient status, smoking status, and bleeding disorders.  2188 received TSA and 2188 received HA. The question is, "among these supposedly similar patients, what determined whether they wound up getting HA or TSA? We'll get back to that question shortly.

The HA patients had a higher rate of any adverse event (7.18% vs 4.8%), death (0.69% vs 0.1%), sepsis (0.46% vs 0.1%), postoperative transfusion (4.62% vs 2.2%), postoperative intubation (0.5% vs 0.1%), and extended length of stay (23.77% vs 13.1%). 

Comment: While these differences are striking, it is apparent that putting in a plastic glenoid does not reduce the risk of death, sepsis, transfusion, intubation or extended length of stay.

As stated above, the possibility of bias arises because a difference in the outcome between treatment groups may be caused by factors that predict which treatment the patient receives rather than the effectiveness of each treatment. HA patients had a statistically significantly higher mortality probability (0.004±0.010 vs 0.002±0.003 and morbidity probability (0.027±0.015 vs 0.021±0.011) at baseline compared with the TSA cohort, even after propensity score matching.  Surgeons may prefer to perform HA for high-risk patients and those with more complex pathology. Less experienced surgeons may elect to perform HA because of its simplicity. Surgeons may be more likely to perform HA on patients that have worse social determinants of health (Economic Stability, Education Access and Quality, Health Care Access and Quality, Neighborhood and Built Environment, and Social and Community Context), which are known to be associated with inferior outcomes.

Thus, while the authors state 

"HA was found to increase the odds of developing these complications when baseline demographics were controlled",

 perhaps a more accurate statement would be 

"Patients for whom the surgeons chose HA were found have increased odds of developing these complications when the selected baseline demographics were controlled."

You can support cutting edge shoulder research that is 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).

Pyrocarbon shoulder hemiarthroplasty - what do we think we know?

Cobalt chrome is a widely used and well-established material for humeral head replacement, known for its strength, durability, and resistance to corrosion. Chrome cobalt implants have a long clinical history and have demonstrated good outcomes. The example below shows a two year followup of a ream and run procedure (see this link) performed with a chrome cobalt humeral head and a titanium alloy stem. The 35 year old patient has experienced full recovery of his shoulder comfort and function. Note the uniform soft tissue layer between the humeral head and the glenoid bone (blue arrows), the absence of glenoid wear, as well as the absence of osteolysis and stress shielding around the stem fixed with impaction autografting (red arrows).




However glenoid wear can occur after hemiarthroplasty. In an effort to reduce wear, interest has been expressed in a pyrocarbon articular surface as an alternative to chrome cobalt.

Pyrocarbon is a form of carbon that is manufactured through a high-temperature pyrolysis process in which the organic material is heated in the absence of oxygen. This material is known for its strength, smoothness, hardness, and resistance to wear and corrosion. Depending on the loading environment, pyrocarbon is reported to have a lower coefficient of friction (0.01 to 0.1) than chrome cobalt (0.1 to 0.4). The reduced friction may be due to:

(1) pyrocarbon's minimal surface roughness resulting from its highly ordered crystalline structure; chrome cobalt has a relatively rougher surface compared to pyrocarbon.

(2) Pyrocarbon exhibits better boundary lubrication properties in comparison to chrome cobalt. Boundary lubrication refers to the mechanism in which the surfaces are self-lubricated by a very thin film - ranging from a few molecular layers to a few micrometers - consisting of molecules adhering to the surface that minimize friction. Chrome cobalt does not possess the same inherent self-lubricating properties as pyrocarbon, but rather relies more on fluid-film lubrication rather than boundary lubrication.

The smoothness and boundary lubrication properties of pyrocarbon may provide advantages in reducing glenoid wear and the inflammation that can result from wear particles. (see In vitro comparison of wear characteristics of PyroCarbon and metal on bone: Shoulder hemiarthroplasty)

Below is a two year radiographic followup of a pyrocarbon head on a short stem as reported in Pyrolytic carbon humeral head in hemi-shoulder arthroplasty:preliminary results at 2-year follow-up

Here are some receond reports of the use of pyrocarbon humeral heads:

Pyrolytic carbon humeral head in hemi-shoulder arthroplasty: preliminary results at 2-year follow-up 2018. 

At the 2-year follow-up, 50 glenoids (86%) showed no progression of erosion compared with their preoperative status whereas erosion was noted in 8 glenoids (14%).

Fracture of pyrocarbon humeral head resurfacing implant: a case report 2020. 

"Our observation put into question the use of pyrocarbon as a humeral head resurfacing implant. The material seems to be too fragile to be used as a resurfacing implant and cannot achieve fixation of the implant to bone."


Promising results after hemi-shoulder arthroplasty using pyrolytic carbon heads in young and middle-aged patients 2021.
Of 16 patients having an average 2 year followup, the survival rate was high (94.1%). One periprosthetic fracture occurred as the only complication during follow-up. Radiographs showed glenoid erosion in one case and subacromial space reduction in two cases.

Pyrocarbon Arthroplasty Implants in the Upper Extremity: A Systematic Review of Outcomes and Pooled Analysis of Complications 2021. 

Shoulder arthroplasty with pyrocarbon complication rate 13%.

Short-term outcomes and survival of pyrocarbon hemiarthroplasty in the young arthritic shoulder 2022. 

At a mean followup of 33 months, the rate of survival of the HA-PYC prosthesis among 64 shoulders was 92%. Revision was performed in 5 patients: 1 conversion to TSA and 4 conversions to reverse shoulder arthroplasty. The severity of preoperative and postoperative glenoid wear had no influence on the functional results. Nonanatomic reconstruction of the proximal humerus (center of rotation of the prosthesis > 3 mm from the anatomic center) occurred in 29% (18 of 62 patients) and was associated with significantly lower functional and subjective results, more complications (subscapularis insufficiency and/or symptomatic glenoid erosion), and a higher risk of revision. The additional 1.5-mm thickness of the metal disc under the pyrocarbon head was found to be the main reason for overstuffing of the prosthetic head.

Mid-term outcomes of pyrolytic carbon humeral resurfacing hemiarthroplasty compared with metal humeral resurfacing and metal stemmed hemiarthroplasty for osteoarthritis in young patients: analysis from the Australian Orthopaedic Association National Joint Replacement Registry 2022.
The authors analyzed 393 primary shoulder procedures, of which 163 were pyrocarbon hemi-resurfacing (unstemmed) procedures,





163 were metal hemi-resurfacing procedures, and 67 were metal stemmed hemiarthroplasties. The cumulative percentage of revision at 6 years was 8.9% for pyrocarbon hemi-resurfacing, 17.1% for metal hemi-resurfacing, and 17.5% for metal stemmed hemiarthroplasty. Pain, prosthesis fracture, and infection were the key reasons for revision of the pyrocarbon resurfacing hemiarthroplasty.

Short to Early-Mid Term Clinical Outcomes and Survival of Pyrocarbon Shoulder Implants: A Systematic Review and Meta-Analysis 2023. 

Two year survivorship of 92%.

Short-term outcomes following 159 stemmed pyrolytic carbon shoulder hemiarthroplasties and how they compare with conventional hemiarthroplasties and total shoulder arthroplasties in patients younger than 60 years with osteoarthritis: results from the New Zealand National Joint Registry 2023. 

Among patients aged <60 years with shoulder osteoarthritis, 48 underwent pyrocarbon hemiarthroplasty compared with 150 who underwent conventional hemiarthroplasty. There was no significant difference in revision rates or clinical outcomes between the groups.

Survivorship of shoulder arthroplasty for young patients with osteoarthritis: An Analysis of the Australian Orthopaedic Association National Joint Replacement Registry 2023
For stemmed hemiarthroplasty with a metal head, the cumulative revision rates at 2 years and 5 years were 7.4% and 16.7%. Glenoid erosion was the most common cause for revision.
For stemmed hemiarthroplasty with a pyrocarbon head, the cumulative revision rates at 2 years and 5 years were 3.5% and 8.9%. Instability was the most common cause for revision.

Pyrocarbon hemiprostheses show little glenoid erosion and good clinical function at 5.5 years of follow up 2023.
31 shoulders underwent PyC hemiarthroplasty; 11 also had concentric glenoid reaming. The mean follow-up was 5.5 years. AP x-rays were analyzed: A line parallel to the superior and inferior glenoid rim was translated to the most medial point of the glenoid surface. A further parallel line was placed on the spinoglenoid notch and the distance between the two lines was measured.




Measurements were scaled using the known diameter of the implanted humeral head component. 
The mean medial glenoid erosion was 1.4 mm over 5.5 years. In the first year there was 0.8 mm of erosion, significantly more than the average erosion per year of 0.3 mm. Mean erosion per year of patients with glenoid reaming was 0.4 mm, without reaming 0.2 mm. Prosthesis survival rate was 100%. There was a weak correlation between erosion and pain improvement and no correlation between erosion and delta Constant score.

Pyrocarbon hemiarthroplasty of the shoulder: a systematic review and meta-analysis of clinical results 2023.
12 studies (536 patients with pyrocarbon hemiarthroplasties) were reviewed with a minimum 2-year follow-up. Radiographically, 22.8% of patients had evidence of glenoid erosion, 10.4% had changes in implant positioning, and 9.9% had tuberosity thinning. In addition, 1.5% of patients had radiographic subacromial space reduction. There was an 8.6% complication rate, with the most common cause being glenoid erosion. There was an overall 7.7% revision rate, with 63% of revisions undergoing conversion to reverse or total shoulder arthroplasty.

Comment: Pyrocabon humeral heads are more expensive than chrome cobalt heads due to the unique properties and specialized manufacturing processes. Chrome cobalt heads have a long and well-established track record with low revision rates. Comparing the clinical value of pyrocarbon to chrome-cobalt will require randomized trials that control for surgeon expertise, patient characteristics and shoulder characteristics as well as knowledge of the costs of the two systems. The reason randomization is essential lies in the fact that without it, 

(1) better surgeons, high volume surgeons, or surgeons with conflicts of interest might exert a selection bias on which patients received pyrocarbon

(2) healthier, better informed or socio-economically advantaged patients may be more likely to receive pyrocarbon.

These and other important variables are essentially impossible to control for without randomization.

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
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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).

Managing the failed anatomic total shoulder

Wear, loosening, and migration of the prosthetic glenoid component can complicate anatomic total shoulder arthroplasty.

Polyethylene wear can cause osteolysis of the bone around the glenoid and humeral components leading to insufficient bone stock and bone quality for re-implantation.

Although there is a trend to manage failed anatomic total shoulder arthroplasties (aTSA) with revision to a reverse total shoulder arthroplasty, such revisions can be complicated by introperative fracture, difficulties in baseplate fixation, postoperative component loosening, instability, infection, neurologic injury and acromial or scapular spine stress fractures.

Some cases of failed aTSA can be successfuly revised to a hemiarthroplasty (HA).

The authors of Revision of total shoulder arthroplasty to hemiarthroplasty: results at mean 5-year follow-up investigated the outcomes reported by patients after conversion from aTSA to HA. Intraoperative glenoid or humeral component loosening was found in all 29 patients.

76% of the patients were satisfied with the procedure. Pain improved in 87% of the patients with mean pain scores improving significantly from 6.2 to 3.1. Simple Shoulder Test (SST) scores improved from a mean of 4.1 to 7.3. 62% had improvement exceeding the SST MCID threshold of 2.4. No significant differences in patient or shoulder characteristics were found in comparing those patients who improved by an amount greater than the MCID of the SST to those patients who improved less than the MCID. However, among the 6 patients who underwent conversion from aTSA to HA with cuff failure, only 3 (50%) attained MCID improvement of SST and 3 (50%) were satisfied with their revision.

59% of the patients had ≥2 positive cultures with the same bacteria; 82% of these were with Cutibacterium. Thus obtaining cultures at the time of revision is important. Furthermore, in view of the observation that over half of the revisions met the definition of having a periprosthetic infection (even though there were no obvious preoperative signs of infection), surgeons should consider complete, rather than partial, single-stage exchange and postoperative antibiotic therapy. Seven (88%) of the 8 patients with a loose humeral component had ≥2 positive cultures with the same bacteria. Surgeons should have an even higher index of suspicion for infection in cases of humeral component loosening.

Four patients (14%) required conversion to total shoulder arthroplasty: 2 to anatomic and 2 to reverse. An additional 3 patients (10%) had a revision HA performed because of persistent pain and stiffness.

There were no intraoperative fractures, problems with component fixation, infections, neurologic injuries or scapular stress fractures.

Comment: While the technique for revision of a failed total shoulder to hemiarthroplasty is not discussed in this paper, there are several options to be considered.

(1) Humeral head component removal, retention of a securely fixed humeral stem, glenoid component removal, debridement, culturing of deep tissue and explants for Cutibacterium, smoothing of the residual glenoid bone, insertion of a new humeral head with modifications of eccentricity, head diameter of curvature, and head thickness as needed to balance the shoulder's smoothness, mobility and stability, followed by a course of antibiotics until the results of the cultures are finalized. Some case examples of this method are shown below. In the case on the left, note the use of an inferiorly excentric humeral head component. In the case on the right, note the upsizing of the diameter of curvature to help distribute the load to the rim of the remaining glenoid bone. Glenoid bone grafting was not used in these cases.

(2) Complete single stage exchange with humeral head and body removal, glenoid component removal, debridement, culturing of deep tissue and explants for Cutibacterium, smoothing of the residual glenoid bone, insertion of a new body and a humeral head with eccentricity, head diameter of curvature, and head thickness as needed to balance the shoulder's smoothness, mobility and stability, followed by a course of antibiotics until the results of the cultures are finalized. The case for this approach is based on the observation that over 50% of cases in this study had culture evidence of periprosthetic infection (PJI), even in the absence of preoperative signs of infection. The problem is that the results of the cultures are not available in time to influence the surgical decision or the decision about antibiotics immediately after surgery. Complete single stage revision would seem to be particularly indicated in cases of humeral component loosening in view of the even higher association with PJI. (see Single-Stage Revision Is Effective for Failed Shoulder Arthroplasty with Positive Cultures for Propionibacterium). See the illustrative case below.

(3) Primary conversion to a reverse with removal of humeral head and body removal, glenoid component removal, debridement, culturing of deep tissue and explants for Cutibacterium, smoothing of the residual glenoid bone, insertion of a reverse total shoulder followed by a course of antibiotics until the results of the cultures are finalized. This approach would seem to be most applicable to shoulders with combined prosthetic and rotator cuff failure - especially if the patient has pseudoparalysis. It should be undertaken with the recognition of a high complication rate as pointed out by the authors of Salvage reverse total shoulder arthroplasty for failed anatomic total shoulder arthroplasty: a cohort analysis

See this related paper What is the optimal management of a loose glenoid component after anatomic total shoulder arthroplasty: a systematic review, that discusses four types of revision: hemiarthroplasty, 1-stage TSA, 2-stage TSA, and RSA, each of which had as high as a 20% re-revision rate!

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).