Glenoid pathoanatomy: what about the B Walch types?

In his classic paper, Morphologic study of the glenoid in primary glenohumeral osteoarthritis, Gilles Walch identified the B1 and B2 glenoids as being common of types of arthritic glenohumeral pathoanatomy in patients presenting for anatomic shoulder arthroplasty. 

An important characteristic of these glenoid types is the posterior decentering of the humeral head on the glenoid, a critical element in the evaluation and management of glenohumeral arthritis.  Note that the degree of decentering was (and remains) defined by the relationship of the humeral head to the face of the glenoid (and not the plane of the scapula), as seen from this figure from his classic article.

The decentering of the head on the glenoid can be evaluated on the standardized axillary "truth" view, as shown in the five examples below.

By the "truth" view, we mean an axillary view obtained with the arm elevated in the plane of the scapula that shows the spinoglenoid notch or "eye" (red arrow) as shown in this Steve Lippitt illustration:

The rationale for evaluating decentering with the arm elevated to a functional position is that CTs or MRIs obtained with the arm at the side may not reveal it, as shown in the two images of the same shoulder shown below. The MRI obtained with the arm at the side does not reveal decentering, whereas dramatic posterior decentering is shown when the arm is elevated to a functional position in the axillary "truth" view.

While often considered together, the B1 and B2 are not the same. The B1 has posterior decentering of the humerus on the glenoid without biconcavity of the glenoid from bony erosion. By contrast, the B2 has posterior decentering of the humeral head on the glenoid with biconcavity of the glenoid as shown in these illustrations from the classic article by Walch.

A third B was added by the authors of A modification to the Walch classification of the glenoid in primary glenohumeral osteoarthritis using three-dimensional imaging.

As can be seen from these figures, the B3 is monoconcave (i.e. no biconcavity) with substantial retroversion and without posterior decentering of the humeral head on the glenoid, i.e. the humeral head is centered with respect to the glenoid.

This point is emphasized by the authors of Quantitative measurement of bony pathology in advanced glenohumeral osteoarthritis who use the term "humeral-glenoid alignment (HGA)" to indicate centering or decentering of the humeral head on the glenoid. HGA is measured as the position of the humeral head center relative to the perpendicular line drawn from the glenoid center point (without reference to the scapular axis). This relationship is shown in a figure from their article showing the centering of the humeral head in a B3 glenoid (i.e. the humeral head is not decentered).

How does all this relate to the practice of anatomic shoulder arthroplasty? A recent article, Why do primary anatomic total shoulder arthroplasties fail today? A systematic review and meta-analysis, is relevant. The authors reviewed a total of 44 studies involving 35,168 aTSA procedures; 2744 failures were identified. The three most prevalent types of failure were: 

(1) implant loosening (26.1%), with 21.7% of failures attributed to glenoid component loosening. 

(2) Rotator cuff insufficiency (17.3%).  

(3) Instability (10.4%) 

Another recent article compared the types of failure in the Kaiser and the Australian Orthopaedic Association databases.Early revision in anatomic total shoulder arthroplasty in osteoarthritis: a cross-registry comparison.

The most common reasons for revision in the AOA experience were instability/dislocation (31.1%), rotator cuff insufficiency (24.2%), and loosening/lysis and implant breakage glenoid insert (11.0% each). The most common reasons in Kaiser experience were rotator cuff tear (32.3%), glenoid component loosening (29.0%), and dislocation and infection (12.9% each). 

While these articles did not study the relationship of glenoid type to loosening or instability, we can venture that because B1 and B2 glenoids demonstrate preoperative posterior decentering, they would be at risk for postoperative instability. The B3, being centered preoperatively would seem less at risk for instability as long as the centering was not disrupted by the arthroplasty.

There are a number of approaches for shoulders with each of the different B types, each of which has its proponents, advantages and limitations. As emphasized in Short-term outcomes of anatomic total shoulderarthroplasty with nonaugmented glenoidcomponent for Walch B2 and B3 glenoidmorphology, all B's are not the same. In fact, each patient and their shoulder is a one of a kind combination. We like to say that each patient is an N of 1.

Here's an approach we commonly use for effectively and durably restoring stability and mobility. Note that usually we do not attempt to "correct" preoperative glenoid version (see Does postoperative glenoid component retroversion following anatomic total shoulder arthroplasty affect clinical outcomes? A systematic review and meta-analysis) and judge the need for an anteriorly eccentric humeral head based on intraoperative testing at surgery with trial components in place (see Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components).

We start with Anatomic total shoulder - preoperative planning and intraoperative decision making, recognizing the different characteristics among the 3 Bs

B1 - conservative reaming without attempting to alter version, preserving glenoid bone stock, excellent carpentry to assure perfect seating of the component, and use of an anteriorly eccentric humeral head to manage excessive posterior translation if that is evident on intraoperative examination with a concentric trial humeral head component in place.

B2 - conservative reaming - just sufficient to convert the biconcavity to a mono concavity without attempting to alter glenoid version, preserving glenoid bone stock, excellent carpentry to assure perfect seating of the component, and use of an anteriorly eccentric humeral head to manage excessive posterior translation if that is evident on intraoperative examination with a concentric trial humeral head component in place.

B3 - conservative reaming without attempt to alter glenoid version, preserving glenoid bone stock, excellent carpentry to assure perfect seating of the component. An anteriorly eccentric humeral head component is rarely necessary because of the absence of preoperative decentering.

For additional information on this approach see:

Anatomic Total Shoulder Arthroplasty with All-Polyethylene Glenoid Component for Primary Osteoarthritis with Glenoid Deficiencies

Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty?

Does glenoid version and its correction affect outcomes in anatomic shoulder arthroplasty? A systematic review

Anatomic total shoulder arthroplasty for posteriorly eccentric and concentric osteoarthritis: a comparison at a minimum 5-year follow-up

Glenoid retroversion does not impact clinical outcomes or implant survivorship after total shoulder arthroplasty with minimal, noncorrective reaming

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Spring 2021

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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).

B0 glenoid with functional decentering in a 44 year old man - what to do?

A 44 year old man had a previously asymptomatic left shoulder until he attempted to separate to young boys who were fighting at school. Since then he has had pain in his left shoulder, especially when he attempts to push with the arm in forward elevation. His ranges of motion are full and symmetrical to the opposite side. His pain is aggravated with cross body adduction and when he pushes forward and upward against resistance. Instability tests were all unremarkable.

An MRI taken with the arm at the side shows the humeral head centered in the glenoid. His posterior labrum appears somewhat hypertrophic (as seen in glenoid dysplasia) and appears detached from his glenoid.



His axillary "truth" view taken in the position of function and in the position most painful for him shows functional posterior decentering of the humeral head on a glenoid lacking a bony concavity posteriorly.




This case may meet the definition of a Walch B0 glenoid: pre-osteoarthritic posterior subluxation of the humeral head. The authors of that article state: "It appears that Walch B0 glenoid is a pathologic condition (initially dynamic, eventually evolving into a static condition) that may lead to posterior erosion of the glenoid, taking place once there is asymmetric increased posterior glenohumeral contact forces and possibly associated with increased glenoid retroversion."

Further discussion of this pathoanatomy can be found at
The B0 glenoid: why does the back of the glenoid wear out?

In the relevant and interesting ASES Podcast - Episode 107 - Glenohumeral Osteoarthritis Etiology Dr. Peter Chalmers and Dr. Brian Waterman conduct a roundtable interview on the etiology of glenohumeral osteoarthritis with Drs. Ben Zmistowski and Jean-David Werthel.

For our patient the question becomes "what can be done to prevent this shoulder from becoming arthritic? Will a posterior labral repair address the functional posterior decentering? Is there a bony procedure that would be more effective?

We are wondering. Share your thoughts 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
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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).

Subluxation in the arthritic shoulder - what is it and what should be done about it?

Subluxation of a joint is defined by the World Health Organization as an "incomplete or partial dislocation" 

Posterior subluxation of the humeral head on the glenoid is shown below in an axillary view taken with the arm in a position of functional elevation. Because it loads the back of the shoulder, this "truth" view may be better at detecting posterior decentering than a CT taken with the arm at the side. See Answering the critical question: "To what degree is the humeral head functionally centered on the glenoid?" in 6 easy steps.

See Functional malcentering of the humeral head and asymmetric long-term stress on the glenoid: Potential reasons for glenoid loosening in total shoulder arthroplasty ("we found that only 25% of the patients demonstrated a fixed posterior malcentering in a relaxed situation, but 85% showed a functional de-centering during elevation of the arm").

The topic of arthritic shoulder subluxation is obviously of great interest in that the number of articles relating to it is increasing each year.

The amount of posterior subluxation of the humeral head on the glenoid can be determined on an axillary projection as described by Walch et al in Primary glenohumeral osteoarthritis: clinical and radiographic classification. The Aequalis Group

Another approach uses the scapular body - rather than the glenoid articular surface - as the reference. In this method a line is drawn from the tip of the medial border of the scapula to the center of the glenoid fossa; the degree of subluxation is defined as the amount of humeral head lying posterior to this line. As shown in the figure below modified from Approach to glenoid bone loss and deformity in B3 and C glenoids: Primary anatomic shoulder arthroplasty, this method will show a substantial amount of "subluxation" in B3 and C glenoids.

However, applying the original Walch method to this example finds that the humeral head is centered in the glenoid (i.e. not subluxated).

When subluxation is defined as the relationship of the humeral head to the scapular plane, it is strongly correlated with glenoid version, as can be seen from the data presented in Association Between Rotator Cuff Muscle Size and Glenoid Deformity in Primary Glenohumeral Osteoarthritis  (correlation coefficient 0.919)

However the relationship of the humeral head to the plane of the scapula does not reveal the degree of centering or decentering of the humeral head in the glenoid. This helps us understand that the difference between an A2 glenoid and a B3 glenoid lies not in the degree to which the humeral head is centered in the glenoid, but rather in the degree of retroversion

Similarly, the humeral head is often centered on the retroverted type C glenoid.

Version can be altered using eccentric reaming, posterior bone graft or augmented glenoid components - each of which may add complexity, cost, and complications.

Thus, in the treatment of symptomatic B3 and C glenoids, the surgeon needs to decide if altering glenoid version is worthwhile. See Glenoid version: acceptors and correctors

The authors of Early to midterm outcomes of anatomic shoulder arthroplasty performed on dysplastic glenoids studied 29 patients with Type C glenoids with minimum 2 year follow-up after anatomic total shoulders with standard components compared to a matched cohort of 58 A1 glenoids. No effort was made to correct glenoid version through reaming or posterior bone graft. They found similar outcomes scores, patient satisfaction, complication rates, and revision rates.

Treatment of posterior decentering is a different matter and can usually be accomplished without changing glenoid version as demonstrated in Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components

A more extensive review of subluxation and its clinical importance can be found in  Subluxation in the Arthritic Shoulder The authors critically reviewed the use and misuse of the term "subluxation" in the characterization of arthritic shoulders. Their bullet points are listed below:

» The term “subluxation” means partial separation of the joint surfaces. In the arthritic shoulder, “arthritic glenohumeral subluxation” refers to displacement of the humeral head on the surface of the glenoid.

» The degree of arthritic glenohumeral subluxation can be measured using radiography with standardized axillary views or computed tomography (CT).

» Shoulders with a type-B1 or B2 glenoid may show more posterior subluxation on an axillary radiograph that is made with the arm in an elevated position than on a CT scan that is made with the arm at the side.

» The degree of arthritic glenohumeral subluxation is not closely related to glenoid retroversion.

» The position of the humeral head with respect to the plane of the scapula is related to glenoid retroversion and is not a measure of glenohumeral subluxation.

» Studies measuring glenohumeral subluxation before and after arthroplasty should clarify its importance to the clinical outcomes of shoulder reconstruction.

Applying the standard definition, "subluxation" refers to the displacement of the humeral head relative to the glenoid articular surface. In the diagram below, posterior displacement of the center of a circle that is fit to the humeral head articular surface (decentering) is shown with respect to the perpendicular bisector (red line) of a line segment connecting the anterior and posterior edges of the glenoid. The amount of displacement (the length of the line segment with double arrows) can be expressed as a percentage of the diameter of the circle.

The figure below shows the posterior displacement of the center of a circle fit to the humeral head articular surface with respect to the scapular body reference (long blue line). The amount of displacement (the length of the line segment with double arrows) can be expressed as a percentage of the diameter of the circle. Displacement of the humeral head relative to the plane of the scapular body is not the same as subluxation in that it does not indicate the degree of displacement of the joint surfaces. 

As shown in the diagram below, the degree of posterior subluxation ( decentering) of the humeral head realative to the glenoid (red symbols) for the different glenoid types is not related to the amount of glenoid retroversion. On the other hand the degree of posterior displacement of the humeral head relative to the scapular body (blue symbols) for the different glenoid types is essentially linearly related to the amount of glenoid retroversion. 

The amount of posterior subluxation of the humeral head relative to the glenoid is affected by the position of the arm when the image is made. In the graph below, note that the amount of posterior decentering for shoulders with B1 and B2 glenoids is greater for axillary views taken with the arm in a position of functional elevation (blue symbols, see x-ray at the top of this post) in comparison to that for CT scans taken with the arm positioned at the side (red symbols). Note also that the A1, A2 and B3 glenoids remain centered in both arm positions.

Comment: The measurement of subluxation of the humeral head in relation to the glenoid is an important element in understanding and managing the arthritic shoulder. The different glenoid types show characteristic patterns of glenohumeral subluxation that are not closely related to the degree of glenoid retroversion. The relationship of the humeral head to the body of the scapula is mostly related to glenoid retroversion and is not a measure of glenohumeral subluxation.

Consistency and appropriate use of the term “subluxation” will enhance our understanding of arthritic glenohumeral pathoanatomy and its management.

Use of the same imaging technique and arm position before and after surgery enables the surgeon to evaluate the effectiveness of arthroplasty in re-centering the humeral head on the glenoid

Thanks to Mihir Sheth, UW shoulder fellow, for his help in preparing this post.

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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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).

Answering the critical question: "To what degree is the humeral head functionally centered on the glenoid?" in 6 easy steps.

Understanding the arthritic shoulder and planning its management depends in large part on determining the anteroposterior position of the humeral head on the glenoid in a position of function.

Documenting the effectiveness of surgical management of the arthritic shoulder depends in large part on determining the postoperative anteroposterior position of the humeral head on the glenoid using the same method that was used preoperatively.

As explained in this video, these goals can most practically be accomplished by obtaining the axillary "truth" view taken with the arm forwardly elevated in a position of function. A proper axillary "truth" view will show the "eye" of the spinoglenoid notch (see arrow).

The axillary "truth" view can reveal the wide range of posterior decentering encountered in clinical practice as shown here (note the "eye" on each of these views):

Quantitating the amount of posterior decentering is easily measured on a properly taken axillary "truth" view using 6 straightforward steps:

1. A line segment (AC) is drawn from the anterior (A) to the posterior (C) edges of the glenoid. 

2. A perpendicular bisector to this line is drawn from the midpoint (B) of AC.

3. X is the center of a circle fit to the humeral articular surface 

4. A diameter of the circle (DF) is drawn through X and parallel to AC 

5. E is the intersection of DF with the perpendicular bisector drawn from B. 

6. The percentage of posterior decentering is (EF/DF – 0.5) × 100%. 

This particular shoulder demonstrates a preoperative posterior decentering of 24%.

Unfortunately, many axillary views are not "truth" views, see such an example below. Functional decentering cannot be measured on such a view.

Unfortunately, decentering in a position of function cannot be measured on a CT scan obtained with the arm at the side (see below):

The amount of decentering preoperatively in a position of function can be compared before and after surgery using the axillary "truth" view.

Examples of the utility of the axillary "truth" view can be seen in "Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components" and in "Total shoulder arthroplasty with an anterior-offset humeral head in patients with a B2 glenoid"

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).

Arthritic glenohumeral pathoanatomy, B3 or not to be.

Characterization of the Walch B3 glenoid in primary osteoarthritis

These authors suggest that a biconcave arthritic glenoid can progress to a uniconcave glenoid through additional wear. They define a "B3" glenoid as one with a single concavity and over 15 degrees of retroversion. This is in apparent contrast to an "A2" glenoid which has a single concavity and less than 15 degrees of retroversion.

They conducted 3-dimensional analysis of CT data on 52 patients with B3 glenoids. In these shoulders the mean retroversion was 24±7 degrees, superior inclination 8±6 degrees, and medialization 14±4 mm.

The position of the humeral head relative to the plane of the scapula was, as would be expected, significantly correlated with the amount of glenoid retroversion. As also would be expected from the definition, in these cases the humeral head was not decentered with respect to the face of the glenoid: i.e. the humeral head remained concentric to the erosion. 

Comment: This article prompts us to consider the surgical management of the retroverted glenoid with a centered humeral head. In our practice shoulders with osteoarthritis or capsulorrhaphy arthropathy often have glenoid version in excess of 15 degrees. Our surgical goal is not primarily to change glenoid version, but rather to stably center the humeral head in a glenoid with a single concavity.

If after insertion of the glenoid component, there is excessive posterior translation of the trial humeral head, we use an anteriorly eccentric humeral head prosthesis

without or with a rotator interval plication.

The issue of categorizing the highly variable glenohumeral pathoanatomy into types has been discussed in a previous post.

A modification to the Walch classification of the glenoid in primary glenohumeral osteoarthritis using three-dimensional imaging.

These authors proposed several modifications to the Walch classification for arthritic glenohumeral pathoanatomy.

They define a B3 glenoid as being monoconcave and worn preferentially in its posterior aspect, leading to pathologic retroversion of at least 15° or "subluxation" of 70%, or both. 

They define a D glenoid as glenoid anteversion or anterior humeral head subluxation. 

They redefine a A2 glenoid as having a line connecting the anterior and posterior native glenoid rims that transects the humeral head. 

As pointed out in prior posts (see link), there many arthritic forms that lie between and among the classically described glenoid types, so that a categorical system has difficulty capturing them all. 

For example in the proposed system, the difference between an 

and a

is based on whether or not the retroversion is greater or less than an arbitrarily selected level of 15 degrees.

In addition there is confusion when the term 'subluxation' - which should be used to describe the relationship of the humeral and glenoid articular surfaces - is used to describe the relationship of the humeral head to the scapular plane (see the discussion in this link). The B3

as described does not show the separation of the the humeral and glenoid joint surfaces that characterizes 'subluxation' in the usual sense of the word.

By contrast the B2, B1, and D meet the usual definition of subluxation - "incomplete or partial dislocation of a joint "

-

An alternative approach can be based on three parametric measurements:

(1) The percent of the glenoid surface that has a pathologic biconcavity (33% posterior in the example below).

 (2) The angle of retroversion of the glenoid face (G) in relation to the scapular body (S)

(3) The centering of the humeral head with respect to the glenoid  (the distance between the anterior glenoid lip and the center of glenohumeral contact (C) divided by the distance between the anterior and posterior glenoid lips (G)).  0.5 indicates a centered humeral head.

Using this system, 

the example "D" glenoid below would be 50% anterior biconcavity, 10 degree retroversion, and decentering of .25 (subluxation).

the example "B3" glenoid below would be 0 biconcavity, 40 degree retroversion, and centering of .5. 

the example "A2" glenoid below would be 0 biconcavity, 15 degree retroversion, and centering of .5. 

Such a system can provide the information necessary for characterizing the pathology and for planning treatment.

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