The reliability, minimal detectable change and construct validity of a clinical measurement for identifying posterior shoulder tightness

Purpose/background: Posterior shoulder tightness (PST) has been implicated in the etiology of numerous shoulder disorders. Therefore, clinicians and researchers must have a reliable and valid method for quantifying PST. The purpose of this study was to investigate the interrater reliability, minimal detectable change at the 90% confidence interval (MDC(90)) and construct validity of an inclinometric measurement designed to quantify PST.

Methods: Two investigators each performed sidelying PST measurements on the non-dominant shoulder of 45 asymptomatic participants in a blinded repeated measures design. Upon completion of the PST measurements, one rater assessed active internal and external rotation for the validity component of the investigation.

Results: Interrater reliability using an intraclass correlation coefficient (ICC) model 2,k was good (ICC 5 0.90). The MDC(90) indicated that a change of greater than or equal to 9 degrees would be required to be 90% certain that a change in the measurement would not be the result of inter-trial variability or measurement error. Construct validity was evaluated using active internal rotation for convergence and external rotation for discrimination. Construct validity was supported by a good to excellent relationship between PST and internal rotation (r 5 0.88) and by an inverse relationship between PST and external rotation (r 5 20.07).

Conclusion: The sidelying procedure described in this investigation appears to be a reliable and valid means for quantifying PST when strict measurement protocols are adhered to. An advantage of this procedure lies in the ability to control scapular position to ensure motion is limited to the glenohumeral joint. Moreover, the use of inclinometry provides an absolute angle of tightness that may be used for intersubject comparison, documenting change, and to determine reference values. Clinicians and researchers should consider the MDC values presented when interpreting change values during subsequent measurement sessions.