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

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.