Quantifying success after total shoulder arthroplasty: the substantial clinical benefit
These authors state that the term "minimal clinically important difference" (MCID) describes the minimum value for meaningful improvement, whereas "substantial clinical benefit" (SCB) describes the value for substantial improvement
At the latest follow-up for their patients having total shoulder arthroplasty, each patient was asked to rate their shoulder as “worse,” “unchanged,” “better,” or “much better” relative to his or her preoperative condition.
They quantified the SCB as the minimum difference in preoperative-to-postoperative outcome that resulted in a patient describing his or her treatment as “much better” compared with “worse” or “unchanged” for 1,568 shoulder arthroplasties with 2-year minimum follow-up performed by 13 shoulder surgeons.
The anchor-based SCB results were American Shoulder and Elbow Surgeons score, 31.5 ± 2.0; Constant Score, 19.1 ± 1.7; University of California Los Angeles Shoulder Rating Scale score, 12.6 ± 0.5; Simple Shoulder Test score, 3.4 ± 0.3; Shoulder Pain and Disability Index score, 45.4 ± 2.2; global shoulder function, 3.1 ± 0.2; visual analog scale, 3.2 ± 0.3; active abduction, 28.5° ± 3.1°; active forward flexion, 35.4° ± 3.5°; and active external rotation, 11.7° ± 1.9°.
Two-thirds of patients achieved the SCB threshold after TSA. Generally, a change of 30% of the total possible score for each outcome metric approximates or exceeds this SCB threshold.
Comment: As we've pointed out previously, the problem with an anchor question, such as "is your shoulder“worse,” “unchanged,” “better,” or “much better” relative to your preoperative condition?" is that it assumes the patient accurately recalls their preoperative condition years later. In this study the time between the preoperative condition and the posing of the question was long: the average follow-up was 44.9 ± 23.8 months (range, 24- 157 months), with an average follow-up of 49.7 ± 27.5 months for aTSA patients and 40.2 ± 18.6 months for rTSA patients.
It seems more robust to document the preoperative and postoperative scores and then express the improvement as a percent of maximal possible improvement (rather than as a percent of the total possible score.
For example the SCB for the Simple Shoulder Test was determined to be 3.4 . Thus an improvement of 4 would be considered a 'successful' outcome. However, an improvement from 0 to 4 is not likely to make the patient as happy with the outcome as an improvement from 7 to 11. The improvement from 0 to 4 represents a change of 33% of the maximal possible improvement, while an improvement from 7 to 11 would represent a change of 80% of the maximal possible improvement.
See this related post:
Quantifying success after total shoulder arthroplasty: the minimal clinically important difference
These authors sought to define a minimal clinically important difference (MCID) for different shoulder outcome metrics and range of motion after total shoulder arthroplasty (TSA) in 466 anatomic TSA (aTSA) and reverse TSA (rTSA) using an anchor-based method: asking the patient to rate his or her shoulder as “worse,” “unchanged,” “better,” or “much better” relative to the preoperative condition.
The anchor-based MCIDs were
Simple Shoulder Test score = 1.5 ± 0.3
American Shoulder and Elbow Surgeons = 13.6 ± 2.3
Constant score = 5.7 ± 1.9
University of California Los Angeles Shoulder Rating Scale = 8.7 ± 0.6
Shoulder Pain and Disability Index score = 20.6 ± 2.6
Global shoulder function = 1.4 ± 0.3
Pain visual analog scale = 1.6 ± 0.3
Active abduction = 7° ± 4°
Active forward flexion = 12° ± 4°
Active external rotation = 3° ± 2°.
Female gender and rTSA were associated with lower MCID values compared with male gender and aTSA patients.
Comment: There are two important limitations to such a study.
First, the patients' answer to the anchor question requires them to recall the condition of their shoulder prior to their surgery a long and variable time ( 44.9 ± 23.8 months (range, 24-157)) prior to the last followup.
Second, the concept of the MCID does not consider that the absolute amount of improvement (e.g. the MCID of 1.5 for the Simple Shoulder Test), may be less important than the amount of improvement expressed as a percent of the maximal possible improvement (I/MPI).
For example an improvement in the SST score by the MCID of 1.5 from a preoperative score from 0 out of 12 to a postoperative score of 2 out of 12 is an improvement of only 2/12ths or only 17% of the maximal possible improvement. Patients with a postoperative SST of 2 are rarely satisfied with the outcome of their arthroplasty (even though they improved by the MCID).
On the other hand, an improvement in the SST score by the MCID of 1.5 from a preoperative score from 8 out of 12 to a postoperative score of 10 out of 12 is an improvement of 50% of the maximal possible improvement (2/4).
Using the SST, this study showed highly respectable average I/MPI of 80% for anatomic total shoulders and an average I/MPI of 76% for reverse total shoulders.
The percentage of maximal possible improvement in the SST is easy to calculate and easily understood by patients.
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