Subluxation of the shoulder - why does it matter?

It matters: the definition affects treatment

The established definition of "subluxation" is:

"Subluxation of the shoulder is a partial dislocation of the shoulder. A humeral head subluxation occurs when the ball of the shoulder doesn't fully dislocate from the glenoid fossa but has shifted out of its normal position". (Massachusetts General Hospital)

"When the ball of the upper arm comes partially out of the socket, this is called a subluxation." (AAOS).

This definition is clearly met by the case below, showing decentering of the humeral head in the glenoid.

As pointed out by Walch et al (see Morphologic study of the Glenoid in primary glenohumeral osteoarthritis) anteroposterior subluxation (or decentering) of the humeral head is commonly seen the arthritic shoulder. The measurements and clinical significance are straightforward

and can easily be obtained on the axillary truth view (see Answering the critical question: "To what degree is the humeral head functionally centered on the glenoid?" in 6 easy steps. and  Natural history of glenoid bone loss in primaryglenohumeral osteoarthritis: how does bone loss progress over a decade?)

The same method can be used to document the postoperative centering of the humeral head on the glenoid (below) in comparison to the preoperative decentering (above).

Recently, however, the term "subluxation" has been confusingly applied to something completely different. Rather than the clinically relevant relationship of the humeral head to the glenoid socket, some have redefined "subluxation" in terms of the relationship of the humeral head to the plane of the scapular body - a relationship of undetermined clinical significance. 

The Evolution of the Walch Classification for PrimaryGlenohumeral Arthritis 

Measurement of "humeral head subluxation according to the scapula axis method".

A 3-Dimensional Classification for Degenerative Glenohumeral Arthritis Based on Humeroscapular Alignment

Measurement of "humeral head subluxation according to the scapula axis method".

Walch B2 glenoids: 2-dimensional vs 3-dimensional comparison of humeral head subluxation and glenoid retroversion 

Measurement of "humeral head subluxation according to the scapula axis method".

Radiographic Severity May Not be Associated with Pain and Function in Glenohumeral Arthritis

Measurement of "humeral head subluxation according to the scapula axis method"..

Focusing on the alignment of the humeral head to the plane of the scapula can lead to the use of augmented components that may not be necessary for centering the head on the glenoid fossa.

Early clinical and radiographic outcomes ofanatomic total shoulder arthroplasty with a biconvex posterior augmented glenoid for patients with posterior glenoid erosion:minimum 2-year follow-up

Typical (A) preoperative and (B) 2-year postoperative axillary lateral radiograph showing the "correction of posterior subluxation" with the posterior augmented all polyethylene glenoid component.

Augmented glenoid components may not be necessary for obtaining a good clinical outcome.

Do glenoid retroversion and humeral subluxation affect outcomes following total shoulder arthroplasty?

An example of a patient with advanced glenoid retroversion and posterior displacement of the humeral head in relation to the plane of the scapula both before and after total shoulder arthroplasty, but with postoperative centering of the humeral head on the gleonoid. (A) The preoperative axillary radiograph showed retroversion of 38°; (B) the postoperative axillary radiograph showed retroversion of 36°. The ASES score at 5-year follow-up was 98.33.

It is interesting to compare these two postoperative axillary radiographs. The first represents the "corrector" philosophy while the second represents the "acceptor" philosophy (see "acceptors vs correctors"). Which looks more robust?

It may well be that focusing on the centering of the humeral head in the glenoid (rather than the relationship of the humeral head to the scapular plane) is what is most important to the clinical outcome.

For more on this important topic, see Subluxation in the arthritic shoulder - what is it and what should be done about it?

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

Follow on twitter: https://twitter.com/RickMatsen or https://twitter.com/shoulderarth
Follow on facebook: 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).

Is this shoulder subluxated?

 

Is this shoulder subluxated?

 

How should the retroverted glenoid be managed? Lessons from glenoid dysplasia.

 Thanks to Mihir Sheth, one of our current shoulder fellows, for helping with this post.

There is much current interest in the management of glenoid retroversion 

The dysplastic glenoid is a malformation characterized by substantial (>25 degrees) retroversion of the glenoid articular surface. The posterior glenoid labrum is typically hypertrophic (red arrow).

Publications on glenoid hypoplasia provide important lessons about glenoid retroversion.

Perhaps the most important recent publication, Early to midterm outcomes of anatomic shoulder arthroplasty performed on dysplastic glenoids evaluated the outcomes of anatomic total shoulder arthroplasties (TSA) with standard (nonaugmented) glenoid components for 29 retroverted dysplastic (type C) glenoids in comparison to a matched group of 29 TSAs for glenoids with non retroverted, minimally eroded glenoids (type A1) using the same surgical technique and implant by the same surgeon.

Type C morphology was defined as having a uniconcave glenoid with greater than 25° of retroversion and characteristic features, including hypoplasia of the posteroinferior glenoid or capular neck and reduced glenoid depth. 

There were no significant differences preoperatively among patients with type C and and type A1 glenoids with respect to sex, age, BMI, dominant side shoulder surgery, comorbidities, and length of followup. 

A single surgeon performed all the arthroplasties using a cemented standard (nonaugmented) all-polyethylene glenoid (pegged or keeled) with a press-fit humeral stem. No effort was made to correct glenoid version through reaming or posterior bone graft. No patients underwent posterior capsulorrhaphy. 

In the 29 patients with type C glenoids, there were 4 postoperative complications: aseptic glenoid loosening (2), isolated subscapularis failure (1), and superior migration of the humeral head (1). 1 patient required revision to reverse shoulder arthroplasty (RSA) and 1 patient for whom revision to RSA was recommended, giving an overall complication rate of 14% and revision rate of 7%. 

In the 29 matched cohort patients with type A1 glenoids, there were 10 postoperative complications resulting in a 17% complication rate and a 12% revision rate. All 7 revisions were to RSA for aseptic glenoid loosening at a mean of 7 years from index TSA .

Clinical outcomes and radiographic outcomes were not different between the two groups.

This study found that Walch type C dysplastic glenoids - defined by severe retroversion without posterior humeral head decenting- were effectively and safely managed by standard anatomic total shoulder arthroplasty components without attempting to "correct" glenoid retroversion by high side reaming, bone graft, augmented glenoid components, or reverse total shoulder arthroplasty. The results of TSA for patients with retroverted displastic glenoids were not inferior to those with the anatomically simpler type A1 glenoids that did not have pathologic retroversion.

Hypoplasia of the glenoid. A review of sixteen patients Patients with glenoid dysplasia having high degrees of retroversion can be asymptomatic. Those with symptoms can benefit from a non-operative,  patient-conducted rehabilitation program. A five years followup, most patients were able to return to work with resolution of symptoms. Progressive degenerative joint disease develops in some patients with the onset of refractory symptoms.

Shoulder arthroplasty for osteoarthritis secondary to glenoid dysplasia: an update Fourteen shoulders with advanced degenerative changes of the glenoid articular surface underwent total shoulder arthroplasty.  Prior to insertion of the glenoid component, eccentric reaming of the anterior aspect of the glenoid was used to in attempt to change the glenoid version. Five of the fourteen total shoulders were revised: three for glenoid component failure and two for infection. The authors concluded that in cases of glenoid dysplasia, surgery should be avoided "unless the symptoms are extreme".

Glenoid Dysplasia  Shoulders with glenoid dysplasia characteristically have over 25 degrees of glenoid retroversion. In many patients, there is an extended period of relative normalcy before the onset of symptoms. Interestingly, the humeral head typically remains centered in the socket inspire of the high degrees of retroversion.

Nonsurgical treatment is reasonably successful in younger patients, but premature degenerative changes frequently occur. Although favorable results can be obtained with the use of anatomic arthroplasty, continued subluxation and glenoid component failure can lead to unacceptable outcomes. 

Characterization of the dysplastic Walch type C glenoid

 The humeral is typically centered on a uniconcave glenoid articular surface (red line drawn perpendicular to the center of the glenoid arcticular surface). Because of the retroversion, most of the humeral head lies posterior to the plane of the glenoid (purple line).

A standard glenoid component can be inserted on the glenoid surface without changing glenoid version. 

While this may result in perforation of the cortical bone of the anterior glenoid neck, this does not compromise glenoid component fixation, especially if a component with a fluted central peg is used.

Anatomic shoulder arthroplasty in Walch type C glenoid deformity: mid- to long-term outcomes reviewed 26 of 30 patients having hypoplastic glenoid morphology and glenohumeral osteoarthritis having an anatomic total shoulder arthroplasty (aTSA) followed up at an average of 8.5 years after surgery. The humeral head was typically centered on a retroverted glenoid as shown below.

Seven different surgeons performed the aTSAs. There was a substantial variability in the surgical technique: an augmented component was used in 9 patients; a standard component was used in 17.  Of the 17 patients with non-augmented components, 9 underwent partial correction with asymmetrical reaming, 3 received a mini-inset glenoid component inserted without changing glenoid version, and 2 had an anteriorly offset humeral component. 

Patients were clinically improved and generally satisfied with the outcome. No statistically significant differences in any outcome measure were observed between patients with augmented glenoid components and those with non-augmented glenoid components. One revision to reverse shoulder arthroplasty was performed for instability at 7 years postoperatively after a traumatic dislocation. 

The changes in glenoid version from the use of partial correction or the use of augmented glenoid components was not stated, so the importance of modifying glenoid version is not known for these patients.

Comment: Taken together, these articles indicate that non-operative management is helpful in patients with glenoid dysplasia not having disabling arthritis. For those patients with disabling arthritis, total shoulder arthroplasty can be successful. At present, there is not good evidence supporting the need to "correct" glenoid retroversion in the shoulder with glenoid dysplasia (see Glenoid Version: Acceptors and Correctors). 

It is worthwhile considering whether the approach used by some of these authors to the retroverted dysplastic glenoid with a centered humeral head - no version correction, standard anatomic glenoid component - might also be applicable to the type B3 glenoid which is also retroverted with a centered humeral head.

It is also worthwhile considering whether the application of 3 dimensional CT based planning to shoulders with glenoid dysplasia may lead surgeons to use more complex implants than those standard components successfully used in some of these studies.

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).

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.

Follow on twitter (X): 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 subluxation of the shoulder - what does it mean?

 Subluxation in the Arthritic Shoulder

Posterior subluxation of the humeral head on the glenoid as shown by an axillary view taken with the arm in a position of functional elevation.

It is important to use correct and consistent terms in the analysis of preoperative glenohumeral pathoanatomy and of postoperative glenohumeral relationships. Arthritic shoulder subluxation is obviously of great interest in that the number of articles relating to it is increasing each year.

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

Follow on twitter: https://twitter.com/shoulderarth

Follow on facebook: https://www.facebook.com/frederick.matsen

Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

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

Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link)

The smooth and move for irreparable cuff tears (see this link)

The total shoulder arthroplasty (see this link).

The ream and run technique is shown in this link.

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

Shoulder rehabilitation exercises (see this link).