Basic Science
The minimal detectable change of the Constant score in impingement, full-thickness tears, and massive rotator cuff tears

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Hypothesis

The purpose of this study was to determine the minimal detectable change (MDC) for the Constant score in patients with impingement, a supraspinatus tear, or a massive rotator cuff (RC) tear as observed changes smaller than the MDC might be the result of measurement error.

Methods

The Constant score was recorded in a total of 180 patients, including 34 patients with impingement, 105 with supraspinatus tears, and 41 with massive RC tears. We assessed the MDC in the 3 subgroups and total group using the samples standard deviation (SD), internal consistency (Cronbach α), and standard error of the measurement. Floor and ceiling effects were also reported.

Results

The absolute mean Constant score was 72 (SD, 11.2) in the impingement group, 44 (SD, 14.7) in the supraspinatus tear group, and 46 (SD, 18.9) in the massive RC tear group. There were no floor and ceiling effects for the absolute Constant score. In the total group, the internal consistency was 0.8 and the standard error of the measurement was 8. The MDC was 23 points on the Constant score in the total group and 17, 18, and 23 points on the Constant score for impingement, RC tears, and massive RC tears, respectively.

Conclusion

This study demonstrates that the MDCs of the Constant score are different in patients with impingement, supraspinatus tears, and massive RC tears. Studies reporting the Constant score should be interpreted by use of the population-specific MDC and minimal clinical important change.

Section snippets

Study design

This is a cross-sectional cohort study in which we analyze baseline (i.e., preoperative) data from 3 different studies on shoulder disease collected between 2003 and 2011.11, 14, 15, 24 Study 1 was a cross-sectional cohort study on the etiologic mechanisms of SIS.11 Study 2 was a randomized controlled trial comparing the treatment effect of all-arthroscopic to mini-open RC repair.24 Study 3 was a consecutive cohort study on tendon transfer surgery for massive RC tears.14, 15 Other than the

Results

The baseline characteristics of each subgroup and total group are presented in Table I. Patients with SIS were younger compared with patients with supraspinatus tears (10 years; 95% CI, 6.5-12.7; P < .001) and massive RC tears (11 years; 95% CI, 7.4-14.2; P < .001). An age difference between supraspinatus and massive RC tear groups was not detected (P = .417). Also, gender (P = .056) and affected side (P = .506) were not different between the subgroups.

The mean Constant score was significantly

Discussion

This is the first study reporting on the MDC of the Constant score in patients with SIS, supraspinatus tear, and massive RC tear.20 The MDC was 23 points on the Constant score in the overall group. The MDC was 17, 18, and 23 points on the Constant score for SIS, supraspinatus tears, and massive RC tears, respectively.

The MDC can be used to interpret outcome effects of treatment measured, next to clinical relevance of statistical effects. When using the MDC, clinicians and researchers should be

Conclusion

The MDC of the Constant score was 17, 18, and 23 for patients with SIS, with a supraspinatus tear, and with a massive RC tear, respectively. We suggest the application of the MDC to interpret treatment effects. Observed changes smaller than the MDC might be a result of measurement error due to reliability and variance in the study population. Therefore, perceived changes that are clinically relevant or statistically significant might not be detectable by the outcome measurement in patients with

Acknowledgments

We thank P.B. de Witte, MD, BSc for data acquisition of the impingement patients.

Disclaimer

The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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    This study was funded by the Dutch Arthritis Association, grant number 2013-1-060.

    Ethical Committee approval: The Leiden University Medical Center Institutional Ethics Review Board approved all the conducted studies (P07.123, P07.116, P09.227, and P11.002).

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