The minimal clinically important difference for function and strength in patients undergoing reverse shoulder arthroplasty.
These authors conducted a prospective longitudinal study of 60 patients with a cuff-deficient shoulder treated with a reverse total should (RSA). The Constant score was recorded before surgery and at a 1-year follow-up assessment. At the 1-year follow-up, all patients also filled out a 15-item anchor questionnaire to assess their perception of change in their overall function, forward elevation, lateral rotation, internal rotation, and strength to determine the (minimal clinically important difference) MCID:
1. Compared to your presurgery state, how do you rate the overall function of your shoulder?
2. Compared to your presurgery state, how do you rate the strength of your shoulder?
3. Compared to your presurgery state, how do you rate the forward elevation of your arm?
4. Compared to your presurgery state, how do you rate the lateral rotation of your arm?
5. Compared to your presurgery state, how do you rate the internal rotation of your arm?
2. Compared to your presurgery state, how do you rate the strength of your shoulder?
3. Compared to your presurgery state, how do you rate the forward elevation of your arm?
4. Compared to your presurgery state, how do you rate the lateral rotation of your arm?
5. Compared to your presurgery state, how do you rate the internal rotation of your arm?
The purpose of this study was to determine the cutoff points for the items of the Constant score involved with function and strength. The meaning of the cutoff point is that patients who exceed it almost always perceive a benefit from the treatment performed. The cutoff points for overall function, forward elevation, lateral rotation, internal rotation, and strength in the Constant score were 8, 6, 2, 2, and 11.5 points, respectively.
While the overall Constant score domains of forward elevation, lateral rotation, and strength (except for internal rotation) were each significantly improved at one year after surgery; only 46.7%, 20%, 50%, 45.8%, and 33.3% of the patients, respectively, exceeded the MCID on each domain after surgery.
While the overall Constant score domains of forward elevation, lateral rotation, and strength (except for internal rotation) were each significantly improved at one year after surgery; only 46.7%, 20%, 50%, 45.8%, and 33.3% of the patients, respectively, exceeded the MCID on each domain after surgery.
The authors concluded that a statistically significant improvement in the Constant score can be expected after a RSA for a cuff-deficient shoulder, but a considerable number of patients do not reach the MCID in the function and strength domains. Small improvements in rotation are perceived to be beneficial by patients, whereas large improvements in forward elevation are required for the improvement to be perceived to be beneficial.
Comment: This is an important paper in that it contrasts the physician-assessed metrics of range of motion and strength with the patient-assessed metrics of perceived improvement. From their study we see that it is easier to show 'statistically significant' improvement in the former than in the latter. In that delivering improvement perceived by the patient is our goal, we may need to focus more on patient-reported outcomes.
For these reasons, many surgeon investigators prefer patient reported outcomes - such as the Simple Shoulder Test - that enable follow-up whether or not the patient is able to return to the office, are free from observer bias, and that do not require standardization of those making measurements.
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