Do lateralization and distalization after reverse total shoulder have a clinically significant relationship with patient outcome?

There are a host of variables that may affect the clinical outcome of reverse total shoulder arthroplasty. A number of authors have attempted to relate distalization and lateralization to outcome scores. For example in Managing rotator cuff tear arthropathy: a role for cuff tear arthropathy hemiarthroplasty as well as reverse total shoulder arthroplasty, the authors found that the postoperative position of the center of rotation and greater tuberosity on anteroposterior radiographs did not correlate with the clinical outcomes for either procedure.

The authors of How To Choose The Best Lateralization And Distalization Of The Reverse Shoulder Arthroplasty To Optimize The Clinical Outcome In Cuff Tear Arthropathy investigated the effect on the 1 year ASES score of combinations of lateralization and distalization of 62 patients having reverse total shoulder arthroplasty performed for cuff tear arthropathy. They measured lateralization by the LSA as shown below





and distalization by the DSA as shown below.







They found the correlation between ASES score and LSA to be = -0.43 and the correlation between ASES score and DSA to be 0.39; both values lying in the "moderate" range.


The accepted value for minimal clinically important difference for the ASES score in total shoulder arthroplasty is 20.9


The DSA of patients with ASES scores > 76 was 48.55 while the DSA of patients with ASES scores < 76. was 37.82, a difference of 10.7.


The LSA of patients with ASES > 76 was 86.43 while the LSA of patients with ASES scores <76 was 100.09, a difference of 13.7.


Thus neither measurement exceeded the threshold for clinical significance.


The authors suggest that optimal LSA should be no more than 90.5° yet of the 24 patients with LSA > 90.5 degrees 75% had ASES scores >76. Furthermore, what should be the lower limit of the LSA?







The authors also suggest that the optimal DSA should be no less than 37.5°, yet of the 17 with DSA less than 37.5, 65% had ASES scores >76. Furthermore, what should be the upper limit of the DSA?




Comment: This is a well done study that effectively uses scatter plots to show all their data. This type of presentation lends itself to an understanding of the variability in the studied relationships.


As the authors point out in their discussion, prior authors have come to varying conclusion about the clinical (rather than statistical) significance of the relationships between distalization angles and lateralization angles.


It seems curious that distalization (a linear dimension) is being measured as an angle, rather than as a linear dimension (see yellow line) and






that laterialization (a linear dimension) is being measured as an angle, rather than as a linear dimension (see yellow line).




Both lateralization and distalization affect deltoid tension, moment arms, center of rotation, stretch on the brachial plexus, the stabilizing compressive force across the articulation, the function of the remaining cuff muscles, the ability to repair the subscapularis and more. We need to know what is the "sweet spot" when the effects of these two variables are considered together?

Finally, distalization and lateralization do not reflect other clinically important variables, such as glenoid tilt, baseplate seating, baseplate fixation, as well as baseplate-bone contact. To determine the relationship of ASES score to the geometry of the reverse total shoulder arthroplasty, a multivariable analysis would be required.

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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 - 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. 

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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).

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