Shoulder instability

Glenohumeral instability is one of the most common disabling conditions of the shoulder. Yet given the great flexibility of the joint and the small, shallow socket provided by the glenoid

it is a wonder that the shoulder remains as stable as it does with everything we ask it to do

In order to understand, evaluate and manage shoulder instability, one needs to understand how the joint is normally stabilized. Our late fellow, Doug Harryman, did a great job explaining shoulder stability in these two videos: Shoulder Mechanics 1 and Shoulder Mechanics 2.  

The principles of shoulder stability are detailed in Chapter 3 of the freely available Practical Evaluation and Management of the Shoulder (see this link.). 

While the knee is stabilized by ligaments that remain isometric through its range of flexion and extension, the shoulder has no isometric structures that limit its range of motion. The surrounding soft tissues remain lax in most functional positions of the shoulder, except those performed at the extremes of shoulder motion (such as in the baseball pitch shown above).

 (N.B.: laxity is not the same thing as instability (see Laxity of the normal glenohumeral ioint: A quantitative in vivo assessment)

While the hip is stabilized by a deep acetabular socket (which limits hip range of motion when its rim is contacted by the femur), the shoulder's socket is shallow, allowing it a great range of impingement-free motion.

The essential mechanism stabilizing the shoulder is concavity compression, a mechanism that functions throughout the range of shoulder motion. Just as the compressive effect of gravity stabilizes the golf ball in the small, shallow concavity of the tee

the glenohumeral joint is stabilized when the net force on the humeral head compresses it into the small, shallow glenoid concavity of the glenoid

As long as the net force acting on the humeral head passes within the glenoid concavity, the joint is stable. The glenoid arc provides a range of positions in which this condition can be met.

The glenoid bone, cartilage and labrum each contribute to the concavity.

The concavity is less in the anteroposterior direction than in the superiorinferior direction.

As a result, the joint's stability from front to back is less than its stability from top to bottom.

If the concavity is compromised, the range of stable positions is reduced.

As pointed out in A Prospective Analysis of Patients With Anterior Versus Posterior Shoulder Instability, while anterior instability is often traumatic, posterior instability more commonly arises from repeated overloading and wear of the posterior supporting structures from pushing and lifting activities that differentially load the back of the joint. 

Recurrent posterior instability may be accompanied by progressive loss of the supportive posterior glenoid cartilage and bone (see Prospective Evaluation of Posterior Glenoid Bone Loss After First-time and Recurrent Posterior Glenohumeral Instability Events).

 

Stability is also compromised if the net force is not directed within the glenoid concavity.

Fortunately, the scapula can usually be positioned so that the concavity is aligned with the compressive force.

For example, if the hand pushes forward while the scapula is retracted, the force on the humerus is not aligned with the glenoid socket and stability is threatened.

However, if the hand pushes forward while the scapula is protracted, the force on the humerus is closely aligned with the glenoid socket, so stability is optimized.

Functional instability has been defined as instability from pathological muscle activation patterns resulting in malalignment of the net humeral force with the glenoid (see Characteristics of functional shoulder instability). 

Often functional instability can be managed by patient education and physical training to strengthen the cuff muscles that provide compression of the humeral head into the glenoid concavity while avoiding positions that risk force malalignment (such as press ups without scapular protraction as shown earlier).  In refractory cases, muscular retraining may be enhanced by using electrical stimulation (see Shoulder-Pacemaker Treatment Concept for Posterior Positional Functional Shoulder Instability: A Prospective Clinical Trial).

The specifics of surgical treatment for glenohumeral instability are beyond the scope of this post. However, understanding the concavity compression mechanism of shoulder stability can help guide practice: 

(1) when instability results from deficiencies in the labrum, cartilaginous lip, or glenoid bone, consider restoring the glenoid concavity through Bankart repair or bony procedures

(2) when instability results from malalignment of the net humeral force with the glenoid, consider restoring the constraints to excessive motion, using capsular repair/shift, rotator interval plication and/or remplissage.  

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).

Issues for anatomic total shoulder - what do they mean for surgeons and patients?

Anatomic total shoulder arthroplasty (aTSA) is the standard surgical treatment for disabling arthritis in shoulders with an intact rotator cuff. It has an established track record of safety and effectiveness extending back over 60 years. 

Here are some of the recent publications regarding anatomic total shoulder arthroplasty.

aTSA in the younger patient and patients with prior instability

See: Why do patients under the age of 50 do less well after anatomic total shoulder arthroplasty?

In addition the authors of A history of shoulder instability is more common in young patients undergoing total shoulder arthroplasty found that patients under 50 years of age were less likely than their older counterparts to have primary osteoarthritis. They were four times more likely to have a history of shoulder instability, over twice as likely to have had prior ipsilateral shoulder surgery of any type, and six times as likely to have had prior ipsilateral shoulder stabilization surgery. Evidently, shoulder instability damages the shoulder's articular cartilage and the stabilizing soft tissues in a manner that increases the risk of secondary arthritis. This finding is consistent with Comparison of patients undergoing primary shoulder arthroplasty before and after the age of fifty which found that only 21% of the younger patients had primary osteoarthritis, whereas 66% of the older patients had that diagnosis. These studies indicate that patients <50 years of age have more complex forms of arthritis, an observation that may help explain the inferior outcomes of shoulder arthroplasty in younger individuals.

Outcomes of Total Shoulder Arthroplasty in Patients with Prior Anterior Shoulder  Instability: Minimum 5-year Follow-up presented 27 male and 9 female patients having total shoulder arthroplasty after prior anterior shoulder instability (ASI).

13 males and 2 females with instability managed non-operatively underwent TSA at an average age of 64 years
14 males and 7 females with prior instability surgery (10 open and 11 arthroscopic) underwent TSA at an average age of 50.6 years.

 

While patient reported outcomes were similar, 6 of 21 (28.6%) TSAs failed in patients with prior surgery for ASI but there were no failures in the nonoperative ASI group.

Kaplan-Meier survivorship analysis demonstrated statistically superior survivorship in patients without prior ASI surgery (100% at five years) compared to those with prior ASI surgery (79% at five years). 
The difference in survivorship between patients with prior open  (72.7%) versus arthroscopic surgery (87.5%) at 5 years was not statistically significant.

aTSA outcomes for the patient with a weak shoulder

In Clinical Outcomes of Anatomic Versus Reverse Total Shoulder Arthroplasty in Primary Osteoarthritis with Preoperative External Rotation Weakness and an Intact Rotator Cuff: A Case-Control Study  defining preoperative external rotation weakness as strength ≤7.2 pounds, the authors compared 74 weak patients having aTSA to 74 patients with normal strength having aTSA.
Despite weak aTSAs having poorer preoperative strength in FE and ER, neither of these deficits were noted postoperatively compared to the normal cohort.  Postoperative outcome scores, rates of complications and need for revision surgery did not differ between the groups. The clinical outcomes showed greater improvement for the shoulders that were weak before surgery.

aTSA outcomes for the patient with a stiff shoulder

In Clinical outcomes of anatomic vs. reverse total shoulder arthroplasty in primary osteoarthritis with preoperative rotational stiffness and an intact rotator cuff: a case control study defining preoperative stiffness as ≤0 of passive external rotation (ER), the authors matched stiff aTSAs (n 257) 1:3 to non-stiff aTSAs.  Despite stiff aTSAs having poorer preoperative range of motion and functional outcome scores for all measures assessed, postoperative outcome scores, rates of complications and need for revision surgery did not differ between the groups. The improvement in active motion was greater for the stiff group.

       

What are the risk factors for complications after aTSA? Can they be modified; if not can they be anticipated and managed?

Prior research has shown that disparities in social determinants of health may account for 80% of the variability in patient treatment outcomes, while the quality of care accounts for as little as 20%. Disparities in social determinants of health are categorized as economic (e.g. unemployment), educational (e.g. illiteracy), social (e.g. incarceration), healthcare (e.g. inability to access quality medical care), and environmental (e.g. exposure to health hazards). 

The authors of Social Determinants of Health Disparities Impact Postoperative Complications in Patients Undergoing Total Shoulder Arthroplasty used a national insurance claims database to identify patients having a primary TSA with at least two years of follow-up.

Patients were grouped in one of two cohorts: (1) patients with no history of SDHD (Control) and (2) patients with a history of SDHD (SDHD group) prior to TSA. With the application of the revised Z-codes, the number of TSA patients recognized has having SDHD is rising dramatically.

The SDHD and control groups were matched 1:1 for comorbidities and demographics prior to conducting multivariable analysis for 90-day medical complications and 2-year surgical complications. There were 8,023 patients in each group. In the SDHD group, 6,486 (80.8%) patients had an economic disparity, 1,519 (18.9%) patients had a social disparity, 354 (4.41%) patients had an environmental disparity, 54 (0.67%)  patients had an educational disparity, and 14 (0.17%) patients had a health disparity.

The SDHD group had over two times higher odds for each of the major 90-day medical complications: heart failure (OR 3.7), cerebrovascular accident (OR 2.5), renal failure (OR 2.9), deep vein thrombosis (OR 3.16), pneumonia (OR 2.8), sepsis (OR 4.9), and urinary tract infection (OR 2.6). The SDHD group had significantly higher odds (OR 1.45) for revision surgery within 2-years following TSA. 

It is evident that evaluation of potential candidates for shoulder arthroplasty should include documentation of social determinants of health (e.g. employment status, social situation, etc.). Shoulder arthroplasty is rarely an emergency. While the patient's economic, social, environmental, educational and health disparities may be difficult to modify in a timely manner, there is time to anticipate the consequences of theses disparities and make plans for managing the associated adverse effects.

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).

Instability and dislocation after reverse total shoulder arthroplasty - are we any smarter about preventing them?

Instability is one of the most common complications after a reverse total shoulder.

The 56 authors of Predictors of Dislocations after Reverse Shoulder Arthroplasty: A study by the ASES Complications of RSA Multicenter Research Group identified 6,621 patients from a multicenter database with minimum 3 month (mean 19.4, range 3-84) followup after a primary or revision reverse total shoulder (RSA) performed by one of 24 experienced surgeons. The study population was 40% male with an average age of 71.0 years. The rate of dislocation was 2.1% (n=138) for the whole cohort, 1.6% (n=99) for primary RSAs, and 6.5% for revision RSAs.

Dislocations occurred at a median of 7.0 weeks after surgery; 23.0% followed a trauma.

The risk factors for dislocation identified in this study were non-modifiable:
(1) diagnosis other than glenohumeral osteoarthritis with an intact rotator cuff (e.g. fracture non-union, rotator cuff disease, failed prior arthroplasty).
(2) history of postoperative subluxations prior to radiographically confirmed dislocation,
(3) male sex,
(4) trauma
and
(5) no subscapularis repair.


Comment:
These authors did not identify modifiable risk factors for dislocation, such as implant type, implant size, implant position, distalization, lateralization, unwanted contact between the humeral component and scapula, or rehabilitation.

By contrast, the authors of Dislocation following reverse total shoulder arthroplasty found two modifiable risk factors - inadequate soft-tissue tensioning and bony impingement (especially in adduction) -  among 14 early (less than three months after surgery) and 5 late (more than 3 months after surgery) dislocations. Non-modifiable risk factors included male sex and prior surgery on the shoulder. Other findings associated with dislocation included asymmetric liner wear and mechanical liner failure; these factors may be modified by prosthesis design and surgical technique.

The authors of Classification of instability after reverse shoulder arthroplasty guides surgical management and outcomes and Revision for instability following reverse total shoulder arthroplasty: outcomes and risk factors for failure identified four categories of factors that contributed to instability in 36 patients having revision of a reverse total shoulder for glenohumeral instability. Many of these are related to implant design and surgical technique and are, therefore, modifiable. The most common mechanism leading to persistent instability was loss of compression.

 (D/R ratio is the ratio of the depth of the polyethylene cup divided by the radius of the cup's concavity).

As emphasized in The normal shoulder, aTSA, and RSA are stabilized by concavity compression and in the articles referenced above, stability of the reverse requires a compressive force aligned with a competent concavity = concavity compression.

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

Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).

Reverse total shoulder: does physical therapy improve patient satisfaction and reduce instability?

The authors of Active Physical Therapy Does Not Improve Outcomes After Reverse Total Shoulder Arthroplasty: A Multi-Center, Randomized Clinical Trial sought to compare range of motion (ROM), patient-reported outcomes (PROs), postoperative stability, complications and patient satisfaction after reverse total shoulder arthroplasty between patients receiving a structured home exercise program (HEP) (n=46) and those placed on active, supervised physiotherapy (PT) (n=43) in a multi-center randomized clinical trial.

Complications occurred in 13% of HEP and 17% of PT patients. 

There were no significant differences between groups in PROs or ROM at final follow-up.

12% (72/82) of patients described some symptoms of instability within one year postoperatively. 

While 90% (74/82) were satisfied with the outcomes,

 only 76% (62/82) stated that they would have the surgery again, given the opportunity.

Comment: Interestingly a larger clinical trial comparing PT to home exercises has been posted (see Physical Therapy After Reverse Total Shoulder Arthroplasty), but the results are not yet available.

Home exercises have some tangible advantages: less cost, less travel, and greater ability to tailor the program to the specific needs and tolerance of each patient. Offering ready access to the surgical team via email or phone can enable patients to ask questions and to be assured they're on the right track.
 

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

Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).

Reverse total shoulder - the instability problem

In Analysis of 4063 complications of shoulder arthroplasty reported to the US Food and Drug Administration from 2012 to 2016 the authors analyzed the arthroplasty the failure reports mandated by the US Food and Drug Administration for all hospitals.  For the 2390 reverse arthroplasties, the most common failure modes was dislocation/instability (32%), followed by infection (13.8%), glenosphere-baseplate dissociation (12.2%), failed/loosened baseplate (10.4%), humeral component dissociation/tray fracture (5.5%), difficulty inserting the baseplate (4.8%), and difficulty inserting the glenosphere (4.2%). 

In Complications in reverse shoulder arthroplasty the authors point out that the reported overall complication rate of primary RSA was approximately 15%; when RSA is used in the revision setting, the complication rate may approach 40%. The most common complication of RSA was instability, followed by infection, notching, loosening, nerve injury, acromial and scapular spine fractures, intra-operative fractures and component disengagement.

In Outcomes of instability after reverse shoulder arthroplasty: reoperation and persistent instability are common the authors evaluated the outcomes of 50 patients having instability after reverse shoulder arthroplasty (RSA). 40 (80%) required revision surgery while 10 (20%) were treated successfully with closed reduction. There were no significant differences between the revision and closed reduction groups with respect to age, sex, BMI, diagnosis, or nature or number of dislocations.

Patients requiring revision were more likely to have had surgery prior to the reverse total shoulder and had longer average times from the reverse total shoulder to dislocation than those managed by closed reduction (7.6 vs 2.2 months).

Following revision surgery, 17 patients (42.5%) reported recurrent instability, and 14 (35.0%) required additional revision surgery. Of the 14 patients who required additional procedures, 4 continued to have instability (28.6%) and 5 required even further surgery (35.7%). Ultimately, stability was never achieved in 7 of 50 patients (14%) after their index instability event. Patients who required >1 revision operation were more likely to have infections and to have undergone the index RSA as a revision procedure

Five patients had positive culture findings at the time of revision surgery, and 4 were considered to have probable or definitive infections.

Comment: Taken together, these papers point to the magnitude and difficulty presented by instability after a reverse total shoulder arthroplasty. Thus in performing a reverse total shoulder it is important to properly select and position the components, to check for unwanted contact between the humerus/humeral component and the scapula, and to vigorously examine the completed arthroplasty for instability, especially with the arm in adduction, extension and internal rotation.

See also Reverse total shoulder - dislocations and how to avoid them and Acromiohumeral cerclage in reverse total shoulder arthroplasty for recurrent instability

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).

Recurrent dislocations of reverse total shoulder arthroplasty

Acromiohumeral Cerclage in Reverse Total Shoulder Arthroplasty for Recurrent

Instability

Recurrent shoulder instability is one of the most frequent complications following reverse total shoulder arthroplasty (rTSA); by contrast, instability is rare after anatomic total shoulder arthroplasty.

In many cases recurrent instability of an rTSA can be managed by correcting component malposition,  upsizing the diameter of the glenosphere, adjusting soft tissue tension, avoiding unwanted contact between the humeral component and use of a retentive liner for the humeral component.

However, some case are refractory to these approaches. 

These authors describe the 1 year outcomes for 10 patients (4 female/6 male average age 64 years) in which an acromiohumeral cerclage technique was used in which the humeral component was stabilized with nonabsorbable, high-tensile suture tape looped through transosseous acromial drill tunnels as an augment to other approaches to enhance stability.

The acromial holes:

The humeral fixation (left - through holes in prosthesis fin, right - around prosthesis neck): 

These patients had an average of 2.1 revisions prior to revision with suture cerclage

augmentation. Many had procedures prior to their index reverse total shoulder.

At followup, the VAS score decreased from an average of 5.9 to 1.6, the ASES score increased from an average of 28 to 80, and active forward elevation increased from 41 to 130. 

All patients remained stable with well-positioned prostheses since their final operations with no recurrent dislocations or acromial complications. Radiographs are seen below.

Comment: Instability after a reverse total shoulder can be a devastating complication. The results reported here are surprisingly good without recognized complications. Longer term followup with a larger series of patients will be important for assessing the risk of acromial fracture and failure of fixation. Interestingly, the authors state, "although we had no acromial complications with this technique in any patient at an average of 2 years postoperatively, we think there is merit to at least considering removing the cerclage after reasonable period of stability to avoid any catastrophic acromial complications."

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).