Sunday, November 13, 2016

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

Determining the minimal clinically important difference for the American Shoulder and Elbow Surgeons score, Simple Shoulder Test, and visual analog scale measuring pain after shoulder arthroplasty.

Primary anatomic total shoulder arthroplasty (TSA), primary reverse TSA, or hemiarthroplasty was performed in 326 patients. The SST score, ASES score, and VAS pain score were collected preoperatively and at a minimum of 2 years postoperatively (mean, 3.5 years).

The minimal clinically important differences (MCIDs) were calculated for the ASES score, SST score, and VAS pain score using a 4-item anchor question evaluating improvement after treatment. Patients were asked the following: “Since your shoulder replacement surgery, please rate your response to treatment: A, none—no good at all, ineffective treatment; B, poor—some effect but unsatisfactory; C, good—satisfactory effect with occasional episodes of pain or stiffness; D, excellent—ideal response, virtually pain free.” Patients were classified by the anchor question as having “no change” (A group [none] and B group [poor] combined) or “change” (C group [good]). The D group (excellent) was not included in the analysis because this was considered beyond minimal change.

The MCIDs for the ASES score, SST score, and VAS pain score were 20.9 (P < .001), 2.4 (P < .0001), and 1.4 (P = .0158), respectively. 

Duration of follow-up and type of arthroplasty (anatomic TSA vs reverse TSA) did not have a significant effect on the MCIDs (P > .1) except shorter follow-up correlated with a larger MCID for the ASES score (P = .0081). 

Younger age correlated with larger MCIDs for all scores (P < .024). Female sex correlated with larger MCIDs for the VAS pain score (P = .123) and ASES score (P = .05).

Patients treated with a shoulder arthroplasty require a 1.4-point improvement in the VAS pain score, a 2.4-point improvement in the SST score, and a 21-point improvement in the ASES score to achieve a minimal clinical importance difference from the procedure.

Comment: MCID is one way of looking at the amount of improvement, but it has a problem. Consider two patient having a shoulder arthroplasty, each with an improvement of 3 in the SST score (both exceeding the 2.4 MCID improvement).

Their outcomes are not the same. For that reason we use both the preoperative to postoperative change in the SST as well as the percent of maximal possible improvement to characterize the result:

Here we can see that Smith only improved by 27% of the maximal possible improvement, whereas Jones improved by 75% of the maximal possible improvement (even though the improvement in both cases exceeded the MCID).

We've found that the concept of %MPI is easier to explain to patients than MCID.

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