Shoulder arthroplasty: how should we measure the benefit?

Treatment Effects of Reverse Total Shoulder Arthroplasty – A Simple Method to Measure Outcomes at 6, 12, 24 and 60 Months for Each Patient

These authors used a treatment effect effects (TE = (preoperative score – postoperative score) /
preoperative score) to assess outcomes in 183 patients with unilateral cuff arthropathy (Hamada grades >=2) treated with reversed total shoulder arthroplasty (RSA). The patients were assessed with the ASES questionnaire.

Two years postoperatively the mean ASES score improved from 20.5 to 78.7.

The 2 year TE's ranged from 1 to 0.09. We had no patient with a negative TE. A higher Hamada grade was associated with better TE’s.

Patients with higher ASA grade had lower TE’s. 

The mean TE’s diminished with time:  0.77 at 6-months, 0.81at 1 year, 0.76 at 2 years and 0.73 at 5 years.

Comment: Results of arthroplasty have been reported in a number of different ways. 

Let's use the example of a shoulder that improved from 21 to 79.

(1) Post operative score - 79

(2) Amount of improvement: Post operative score - preoperative score = 58

(3) Amount of improvement divided by preoperative score: (Post operative score - preoperative score)/preoperative score) = 2.8

(4) Percent of maximum possible improvement: 100*(Post operative score - preoperative score)/(perfect score-preoperative score) = (79-21)/(100-21) = 74%

It seems that #4 has the advantage of showing the amount of improvement in relation to the potential amount of improvement. This is easy to explain to patients: "this operation will not make your shoulder normal, but in our experience our average patient is improved by 74% the way to a normally functioning shoulder."

While there is current enthusiasm for the MCID (Minimal clinically important difference) the best methodology for determining the MCID is uncertain resulting in MCID valued for the ASES score ranging from 6 to 21 (see this link).

But the MCID has an additional problem
If we take a typical value for the ASES MCID of 20, an improvement from 60 to 79 would fail to meet the criterion of improvement by the MCID yet it would yield an improvement of 90% of the maximum possible improvement.

On the other hand, an improvement from 21 to 42 would meet the criterion for improvement by the MCID, but would only represent 27% of the maximum possible improvement.

Which of these is the better outcome?

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