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.

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
Follow on facebook: https://www.facebook.com/shoulder.arthritis
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).

Minimum Clinically Important Difference (MCID) - how useful are these values?

Minimum Clinically Important Difference: Current Trends in the Orthopaedic Literature, Part I: Upper Extremity A Systematic Review

The minimum clinically important difference (MCID) for different patient reported outcomes (PROM) represent a proposed threshold value to be used in determining if a change is clinically significant. These authors point out that efforts at calculating the MCID have yielded multiple and inconsistent values. They reviewed the most recent (2014-2016) publications in leading journals to explore the limitations of its current uses, and to clarify the underpinnings of MCID calculation.

Of 1,709 clinical science articles that utilized PROMs, a MCID was referenced in 129 (7.5%). 

52 (40.3%) of  the129 were related to the upper extremity. 5 (9.6%) of 52 independently calculated MCID values, and 47 (90.4%) of 52 used previously published MCID values.

MCIDvalues were considered or calculated for 16 PROMs; 12 of these were specific to the upper extremity. 

Six different methods were used to calculate the MCID. 

Calculated MCIDs had a wide range of values for the same PROM (e.g., 8 to 36 points for Constant-Murley scores and 6.4 to 17 points for American Shoulder and Elbow Surgeons [ASES] scores). 

The authors concluded that "determining useful MCID values remains elusive and is compounded by the proliferation of PROMs in the field of orthopaedics. The fundamentals of MCID calculation methods should be critically evaluated. If necessary, these methods should be corrected or abandoned."

Comment: In determining the MCID for a PROM, the investigator attempts to tie the amount of change in the PROM to some sort of an "anchor" global assessment: i.e. "improved" or not, "better" or not, "satisfied" or not. The problems with these types of "anchor" is that they are imprecise and poorly defined. Does "improved" mean that there is an overall improvement in the condition from 6 months ago, 1 year ago or 2 years ago. If the latter, how reliably can the patient recall the shoulder's condition 2 years ago? How much of an improvement is required to establish the anchor? Does "satisfied" mean that the condition of the shoulder is different or that the care was satisfactory? As the authors state, "Unfortunately, there is no consensus agreement on what anchor or even specific anchor level (or levels)would best express a minimum important change." Beyond these issues with the anchor, there are important differences in the way data are analyzed to determine the MCID.

Furthermore, a specific MCID needs to be determined for each PROM and for each diagnosis and for each treatment. What should we do if different authors report different values for the MCIDs for a given PROM (see above examples for Constant and ASES when the values vary by >400%).

The concept of the MCID implies that - if we take 17 points on the ASES score as being the MCID - the improvement from an ASES score from zero to 17 has the same significance as the improvement from 80 to 97. It seems doubtful that the patient would see it that way.

Perhaps even more importantly is that the concept of the MCID is difficult to communicate to our primary customers: our patients. How exactly would you talk about the expected outcome of a procedure in terms of the MCID?

In our experience, the percent of maximal possible improvement addresses may of the shortcomings of the MCID. The %MPI is easily determined as the preoperative to postoperative change in the PROM divided by the difference between a "perfect" score on the PROM and the preoperative score.
The advantages of this approach are:
It does not require that the patient try to recall the pretreatment condition of the shoulder.
It does not require patients to answer an anchor question, such as "are you improved?"
It does not create a somewhat arbitrary dividing line between a good result and otherwise: is a chance in ASES score of 16 really different than an ASES score of 18?
It does not require a choice of among different methods of calculations to derive the value.
And, importantly, it the percent of maximal possible improvement is easy to explain to the patient.

The interested reader may like to visit these posts for additional examples and explanations:

Measuring clinical outcomes from total shoulder arthroplasty - it is simpler than what we might have thought

How much improvement in the SST, ASES, and VAS score is clinically significant?

=====

We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art" regarding this radically conservative approach to shoulder arthritis at this link and this link

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

How you can support progress in shoulder surgery

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