Reverse total shoulder arthroplasty: do lateralization and distalization correlate with clinical outcome?

Surgeons want to know how the postoperative position of the humerus in relation to the scapula relates to the clinical outcome after reverse total shoulder arthroplasty (RSA).

The authors of The lateralization and distalization shoulder angles are important determinants of clinical outcomes in reverse shoulder arthroplasty studied these relationships in 46 patients having RSA for cuff tear arthropathy (CTA) using measurements of the lateralization shoulder angle (LSA) and the distalization shoulder angle (DSA) as shown below. Four different implant combinations were included.

Although they found positive correlations between the LSA and the ADLER score and the Constant score, they found no significant correlations between the LSA and ASES, SST, or SSV scores.

While they found negative correlations between the DSA and the ADLER score, they found no significant correlations between the DSA and the total Constant, ASES, SST, or SSV scores.

 

More recently the authors of Lateralization and distalization shoulder angles do not predict outcome in reverse shoulder arthroplasty for cuff tear arthropathy reviewed a larger series of 630 primary RSAs for patients with CTA. Five different implants were used.  The regression calculations for LSA or DSA did not reveal significant associations with any of the clinical outcomes.

In Influence of humeral lengthening on clinical outcomes in reverse shoulder arthroplasty no clear relationship between humeral lengthening and clinical outcomes was identified. 

In Negligible Correlation between Radiographic Measurements and Clinical Outcomes in Patients Following Primary Reverse Total Shoulder Arthroplasty the importance of radiographic measurements and their correlation with clinical and functional outcomes following rTSA was found to be limited. 

In Does glenohumeral offset affect clinical outcomes in a lateralized reverse total shoulder arthroplasty? the magnitude of lateralization did not significantly affect the clinical outcomes. 

In Medialized vs. lateralized humeral implant in reverse total shoulder arthroplasty: the comparison of outcomes in pseudoparalysis with massive rotator cuff tear  the postoperative active elevation range and functional outcomes were not affected by medialization or lateralization of the humeral implant. 

Finally, the authors of Managing rotator cuff tear arthropathy: A role for cuff tear arthropathy hemiarthroplasty as well as reverse total shoulder arthroplasty studied the postoperative relationships in 58 patients having RSA for CTA, including: 

(1) the superior/inferior position of the greater tuberosity in relation to the acromion tip

(2) the medial/lateral position of the greater tuberosity in relation to the acromion  tip

(3) the superior/inferior position of the center of rotation in relation to the bony glenoid center

(4) the medial/lateral position of the center of rotation in relation to the bony glenoid center

(5) the abduction moment 

(6) the distance from the center of rotation to the greater tuberosity

(7) the distance from the center of rotation to the acromion 

As in the prior reports, none of these parameters were significantly associated with clinical outcome.

Comment: Factors other than postoperative radiographic parameters are responsible for the amount of improvement in patient comfort and function following RSA.

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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).

Reverse total shoulder - avoiding excessive humeral lateralization

The position of the reverse humeral cup can be guided either by the humeral diaphysis or by the humeral metaphysis. In many humeri, a prosthesis that fits snugly in the diaphysis may place the humeral cup in an excessively medial position - in other words the humeral shaft is excessively lateralized. There are at least three potential problems that can result: (1) the humeral cup may not fit in the metaphysis resulting in loss of rotational control of the implant, (2) the lateralized humerus may abut against the undersurface of the acromion risking acromial/spine fractures, and (3) lateralization may excessively tighten the repaired subscapularis and residual rotator cuff.

On the other hand, inserting the prosthesis so that the cup is centered in the metaphysis may require using a stem that does not snugly fit in the diaphysis. In such a case the fit of the stem in the diaphysis can be secured using impaction grafting. This method is detailed in this video. An example is shown in the radiograph below. Note the lateral position of the stem in the canal, Had a canal fitting implant been used, the humeral cup would have been more medial and would not have fit securely in the metaphysis.

The authors of A Method to Facilitate Improved Positioning of a Reverse Prosthesis Stem During Arthroplasty Surgery: The Metaphyseal-centering Technique point out that the relationship between the diaphysis and the metaphysis is not constant among humeri

As shown in the video, the "metaphyseal-centering technique" gives priority to the positioning of the shell portion of the humeral prosthesis rather than to the stem of the implant. To ensure that a centralized shell position is achieved within the proximal humerus, the stem portion of the humeral prosthesis may need to be purposely undersized and positioned eccentrically within the humeral diaphysis. Bone autograft is used in such cases to improve the fit and fixation of the stem within the humeral canal. 

They point out in the figure below, that if the stem fits snugly in the canal, the cup may be too medial (left) or too lateral (right). 

By contrast, using metaphyseal centering with appropriately placed impaction grafting (red), both proper metaphyseal placement and secure stem fixation can be achieved even if the stem needs to be placed in valgus or varus. 

 

 

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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)

Shoulder arthritis - x-ray appearance (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).

This is a non-commercial site, the purpose of which is education, consistent with "Fair Use" as defined in Title 17 of the U.S. Code.          

Note that author has no financial relationships with any orthopaedic companies

 

 

Reverse total shoulder - do radiographic measurements relate to the patient outcome?

While reverse total shoulder can be a successful surgery for patients with pseudoparalysis, fracture and failed anatomic arthroplasty, the clinically ideal positioning and type of implant have yet to be determined. For example, while distalization of the glenosphere may lead to an increase in motion and lower risk for scapular notching, it comes with increased risk for neurological injury, acromial/scapular stress fractures and deltoid fatigue. Less distal positioning of the glenosphere may result in collision of the greater tuberosity against the acromion, with risk of loss of range of motion and acromial/spine fracture. 

In an attempt to correlate component type and position with the rate of complications and clinical outcomes, many radiographic measurements have been proposed. 

One example is "arm length" measurement - the distance between the transepicondylar line to the inferior aspect of the acromion. "Humeral lengthening" is the difference between this measurement before and after surgery.

Two other measurements are the lateralization shoulder angle (LSA below left) and the distalization shoulder angle (DSA below right)

It can be seen that these measurements do not directly reflect the position of the center of rotation nor the type or position of the humeral component. A recent article examined the clinical importance of these measurements.

Assessing the validity of the distalization and lateralization shoulder angles following reverse total shoulder arthroplasty

These authors explored the relationship between the distalization shoulder angle (DSA) and lateralization shoulder angle (LSA) and clinical outcome after reverse total shoulder arthroplasty performed in 238 patients by an individual surgeon. 

One group had a 155 degree medialized design  (Anatomical Shoulder Reverse System, Zimmer), 2.5 mm of lateral offset and a 36 mm glenosphere. 

Another group had a 135 degree laterally offset design (AltiVate system from DJO) All females with a lateralized implant had a 32 mm glenosphere with 6 mm of lateral COR offset, while all males had a 32 mm glenosphere with 10 mm of offset.

The reasons for choosing the different prostheses are not provided.

Lateralized prostheses were associated with higher LSAs (88 ± 7) vs. 82 ± 7 for medialized prostheses. While the difference was statistically significant, there was substantial overlap.

The distalization shoulder angle did not correlate with humeral lengthening.

Neither the DSA or the LSA were strongly correlated with 2-year postoperative American Shoulder and Elbow Surgeons score or shoulder range of motion.

Comment: This study did not include a multivariate analysis of the many demographic (e.g. age, sex, diagnosis) and surgical variables (e.g. implant type, size and position) that may influence outcome.  On univariate analysis the authors did not find evidence to support the view that measurements of LSA and DSA have a major influence on the function of a reverse total shoulder. 

Further study, probably using different measurements will be necessary to elucidate the reverse total shoulder geometries that are associated with the best function and the lowest risk of complications. 

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)

Shoulder arthritis - x-ray appearance (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).

This is a non-commercial site, the purpose of which is education, consistent with "Fair Use" as defined in Title 17 of the U.S. Code.          

Note that author has no financial relationships with any orthopaedic companies.

What is the optimal position of a reverse total shoulder?

The lateralization and distalization shoulder angles are important determinants of clinical outcomes in reverse shoulder arthroplasty. 

These authors sought to determine the effect of reverse total shoulder (RSA) lateralization and distalization on final functional outcomes.

They measured the “distalization shoulder angle” (DSA)

 and the  “lateralization shoulder angle” (LSA).

in 46 patients who underwent RSA. Functional outcome and radiographs were evaluated at a minimum of 2 years postoperatively.

LSA values between 75° and 95° were correlated with better active external rotation. Postoperative active anterior elevation, Constant, and Activities of Daily Living Requiring External Rotation scores had a positive correlation with the LSA.

DSA between 40° and 65° resulted in better active anterior elevation and abduction.

However there was a lot of scatter in the data

They looked at four groups of prosthetic techniques

With the exception of the low active external rotation in Group I, there were no discernible differences in outcome among the groups.

Comment: The position of the humerus relative to the scapula after reverse total shoulder arthroplasty is determined by the prosthesis selected and the position in which it is inserted. The classical Grammont approach emphasized medialization and distalization. As shown in the diagrams below by Steve Lippitt, medialization (middle figure below) can slacken the rotators resulting in the loss of active external rotation noted in this study.

More modern approaches emphasize a more anatomic reconstruction with less distalization and more lateralization as shown below.

While the two angles described in this study are of interest, we find it simpler to measure distalization directly as shown here

 and lateralization directly as shown here

Finally, since instability is one of the most common complications of reverse total shoulder arthroplasty,    it is important to prioritize the component geometry and the component position that optimizes the stability for each patient.

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Reverse total shoulder - effects of bony and prosthetic glenoid lateralization

Finite element analysis of glenoid-sided lateralization in reverse shoulder arthroplasty

These authors conducted a 3D finite element analysis (FEA) to evaluate glenoid-sided lateralization in reverse shoulder arthroplasty and compared bony and prosthetic approaches to lateralization. Bony lateralization was accomplished by the insertion of a bone graft between the baseplate and the glenoid. Prosthetic lateralization was accomplished by either increasing the thickness of the base plate or increasing the thickness of the glenosphere.

Stress and displacement were evaluated at baseline and following 5, 10, and 15 mm of bony or prosthetic lateralization. 

Maximum stress for a 36 mm glenosphere without bone graft increased by 137% for the 5 mm graft, 187% for the 10 mm graft, and 196% for the 15 mm graft. Displacement also increased progressively with increasing graft thickness. 

Stress and displacement were reduced with a smaller glenosphere, inferior tilt of the baseplate, and divergent peripheral screws. 

Compared to bony lateralization, stress was lower with prosthetic lateralization through the glenosphere or baseplate. 

Displacement with 5 mm of bony lateralization reached recommended maximal amounts for osseous integration, whereas, this level was not reached until 10–15 mm of prosthetic lateralization. 

Baseplate stress and displacement in this FEA model was lower with a smaller glenosphere, inferior tilt, and divergent screws. 

Bony lateralization increased stress and displacement to a greater degree than prosthetic lateralization.

The authors concluded that at least 10 mm of prosthetic lateralization is mechanically acceptable during RSA, but that only 5 mm of bony lateralization is advised. 

Comment: There seems to be a trend away from the original Grammont design of reverse total shoulder

because of concerns about (1) scapular notching, (2) neurologic consequences of lengthening the arm, and (3) external rotator weakness from medialization of the humerus. With the advent of secure baseplate fixation, surgeons can reduce the notching and neurologic risks with a more anatomic reconstruction that includes East-West tensioning of the residual external rotators and other soft tissues. This lateralization can be accomplished by interposing a bone graft between the baseplate and the glenoid bone 

or by having a lateral offset built into the prosthesis. While bone graft has shown a high healing rate, there is concern about the possibility of compression of the graft with loss of the intended amount of lateralization. Our preference is for an implant system that allows variable lateral prosthetic offset combined with secure baseplate fixation. 

 

This article provides additional support for the use of prosthetic lateralization.

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Reverse total shoulder - the clinical value of lateral offset of center of rotation

Clinical performance of lateralized versus non-lateralized reverse shoulder arthroplasty: a prospective randomized study.

These authors studied the effect of lateralization of the center of rotation in reverse shoulder arthroplasty (RSA) for cuff tear arthropathy (CTA). Thirty-four patients had RSA either with lateralization (n = 17) or without lateralization (n = 17) by use of a 1-cm autologous bone graft ("bony increased offset") of the humeral head for CTA.

At final follow-up, all patients showed significantly increased functional results and clinical outcomes. There were no significant differences in the evaluated parameters. 

If patients with degenerative changes of the teres minor were excluded, the lateralized group showed significantly increased external rotation. Bony integration of the graft could be verified on postoperative computed tomography scans in all patients.

In 4 patients, CT scan evaluation showed acromial stress  fractures (2 in STD group and 2 in BIO group).

RSA with bony lateralization shows a trend toward improved external rotation in lateralized RSA, with a statistically significant improvement in external rotation in patients with an intact teres minor.

Comment: Lateralization of the center of rotation can be accomplished with either the use of graft (as in this case) or with an offset glenosphere (as in technique we use). 

As nice shown in this illustration by Steve Lippitt, in medializing the center of rotation the Grammont-style reverse total shoulder (middle figure) removes the tension and function of whatever rotators may remain intact. Lateralization of the center of rotation (bottom figure) helps restore tension and function if the external rotators are intact (as shown in this study).

As stated here and here we prefer glenoid components that have different amounts of built-in lateral offset so that the tension in the residual external rotators can be adjusted.

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Reverse total shoulder - effects of lateralization of the center of rotation

The effects of progressive lateralization of the joint center of rotation of reverse total shoulder implants.

These authors used a 3-dimensional model to explore the effects of lateralizing the center of rotation (CoR) on the deltoid muscle moment arm and glenohumeral joint contact forces. This model was virtually implanted with 5 progressively lateralized reverse shoulder prostheses. The joint contact loads and deltoid moment arms were calculated for each lateralization over the course of 3 simulated standard humerothoracic motions.

In this model, lateralizing the CoR led to an increase in the overall joint contact forces across the glenosphere. Most of this increased loading occurred through compression, although increases in anterior/posterior and superior/inferior shear were also observed. Moment arms of the deltoid consistently decreased with lateralization. Bending moments at the implant interface increased with lateralization. Progressive lateralization resulted in improved stability ratios.

Comment: These observations are important, but they are also predictable from from a free body diagram (as suggested by the illustration by Steve Lippitt below). When the center of rotation is moved laterally (as in the diagram to the right), the deltoid force becomes increasingly effective in pressing the glenosphere and the humeral cup together, increasing the contact force and the stability by the concavity compression mechanism. The deltoid moment arm is decreased by lateralization (note the change in the distance between the dot at the CoR and the red deltoid muscle). The bending moment at the implant interface (the distance between the dot and the face of the glenoid bone) is increased by lateralization.

The additional benefit of lateralization - distancing the medial humeral component from the lateral glenoid neck - is also seen on these diagrams.

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Reverse total shoulder - lateral offset of the glenoid component - is bone graft best?

Bony Increased-Offset Reverse Shoulder Arthroplasty

In the abstract of this article, the authors state "Reverse shoulder arthroplasty has proven useful in numerous pathologic conditions, such as that of pseudoparalytic shoulder with severe rotator cuff deficiency with or without collapse (so-called cuff-tear arthropathy), rheumatoid arthritis, dislocations and sequelae of proximal humerus fractures, and revision shoulder arthroplasty. Despite the advances beyond the constrained reverse prostheses of the 1970s resulting from Grammont’s principles, problems remain with current systems, with high rates of scapular notching and prosthetic instability. Lateralization of the center of rotation of the shoulder joint has been viewed as a potential solution to these persistent problems, and is included in the procedure known as bony increased-offset reverse shoulder arthroplasty. This article presents our surgical technique for this procedure and promising early results of its use." The article itself is elegantly presented by the highly experienced shoulder surgeon who has exhibited mastery of this method.

The authors performed a prospective study in 42 patients with rotator cuff deficiency to determine whether BIO-RSA would avoid the problems caused by humeral medialization. At a minimum follow-up of 2 years (average, 28 months), 39 of 42 patients (93%) were satisfied or very satisfied with its functional results; 32 of the 42 patients (76%) had good or excellent adjusted Constant-Murley scores. There were no cases of loosening of the glenoid component of the prosthesis. The graft bone used with the prosthesis was observed to have healed to the glenoid in 41 of the 42 patients (98%) on follow-up examination with radiography and CT scanning. Scapular notching occurred in 19% (8 of 42) of the patients. There were no instances of instability of the prosthesis and no instances of reoperation.

Comment: In the early days of the reverse, surgeons avoided lateral offset because of concerns about the loosening moments applied to the glenosphere and a desire to optimize the deltoid moment arm. However, medial placement of the glenosphere is now recognized to risk contact between the medial aspect of the humeral component and the inferior glenoid which can lead to notching and instability. As a result, surgeons are using one of two methods for lateralizing the center of rotation: 

(1) the bony increased-offset reverse shoulder arthroplasty described in this article

and (2) glenoid components with a built-in lateral offset. 

In both instances, the lateralized center of rotation places additional demands on the fixation of the glenoid component to the scapula. Our preference is for glenoid components with a built-in lateral offset as described here and here because (a) the fixation does not depend on healing of a bone graft, (b) the quality of bone available for a bone graft is variable in patients having primary reverse total shoulders, (c) bone graft from the humeral head is not available in revision arthroplasty, (d) the operative time and special instruments for bone graft harvest are eliminated and (e) the central screw can be tightened to compress the glenoid component on the bone of the glenoid without worry of crushing the graft.

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Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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