The Reliability, Minimal Detectable Change and Construct Validity of a Clinical Measurement for Quantifying Posterior Shoulder Tightness in the Post-operative Population

Abstract

BACKGROUND: Posterior shoulder tightness (PST) has been implicated in the etiology of numerous shoulder disorders. Although reliable and valid measures have been described for the non-operative population one does not exist for the post-operative population. STUDY DESIGN: Blinded repeated measures design. PURPOSE: Investigate the intrarater reliability, minimal detectable change at the 90% confidence interval (MDC(90)) and construct validity of an inclinometric measurement designed to quantify PST in the post-operative population. METHODS: One investigator performed PST measurements on the operative shoulder of 23 participants. Passive internal and external rotation measurements were performed for the validity component of the investigation. RESULTS: Intrarater reliability using an intraclass correlation coefficient (ICC) model 3,k was good (ICC = 0.79). The MDC(90) indicated that a change of greater than or equal to 8 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 supported by a statistically significant relationship between PST and internal rotation r = 0.54 and by a relationship between PST and external rotation r = 0.30 which was not statistically significant. CONCLUSION: The sidelying procedure described in this investigation appears to be a reliable and valid means for quantifying PST in the post-operative population. 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. LEVEL OF EVIDENCE: Therapy, level 2b