What is the outcome of shoulder joint replacement arthroplasty? - need to consider all three dimensions.

Clinical research on the effectiveness of shoulder arthroplasty commonly focuses on a single dimension (e.g. the amount of improvement in a shoulder score) and seeks to establish a threshold value for this score in determining  "success" (see Quantifying Success After Reverse Total Shoulder Arthroplasty: the Minimal Clinically Important Percentage of Maximal Possible Improvement ).

Actually, there are three important dimensions in documenting the outcome of shoulder joint replacement:

(1) Satisfaction - the degree to which the outcome realized by the patient met their expectations.

(2) The outcome score (e.g. Simple Shoulder Test (SST), ASES, Constant, SANE, SCV)  achieved - for example using the SST, the outcome score is the number of positive responses to twelve questions regarding shoulder comfort and function. 12 "yes" responses would be a perfect score.

(3) The percent of maximum possible improvement (%MPI) in the outcome scare achieved - this is calculated as the amount of improvement divided by the maximum possible improvement (followup SST score - preoperative SST score)/(12 - preoperative score).

Interestingly, these three dimensions are not closely related.

A patient may be well satisfied by a modest final score and a modest improvement if their surgeon set modest expectations before surgery. Dr Neer referred to this as "limited goals" and he was adept at setting reasonable expectations for his patients. 

Let's consider two different patients achieving an SST score of 10 out of 12 at followup. 

Patient "A" had a preoperative SST score of 9  - thus the %MPI would be ((10-9)/(12-9) or 33%. 

Patient "B: had a preoperative SST score of 2 - thus the %MPI would be ((10-2)/(12-2) or 80%.

Both of these patients may be satisfied if the surgeon suggested preoperatively that the expected outcome would be about 10 out of 12 SST functions.

Both of these patients may be unsatisfied if the surgeon suggested preoperatively that the expected outcome would be 12 out of 12 SST functions.

Many publications have advocated defining "thresholds", i.e. certain values for each of these parameters above which the outcome would be defined as being successful and report the percent of patients exceeding the threshold. However, proposed "thresholds" vary for different patient populations, diagnoses and treatments.

It is more useful to present the raw data for each of the three dimensions, for example in 100 patients having total shoulder arthroplasty for osteoarthritis the average final SST score was 10, the average %MPI was 60% and the average patient was very satisfied

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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)