The purpose of this study was to investigate the interrater reliability, minimal detectable change (MDC) and construct validity of an inclinometric measurement technique designed to quantify PST.
Construct validity was evaluated using active internal rotation (IR) for convergence given the direct relationship between posterior capsuloligamentous tension and IR. External rotation (ER) was used for discrimination as biomechanical studies have identified an absence of influence between PST and ER.
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.
Interrater reliability using an intraclass correlation coefficient (ICC) model 2,k was good (ICC 0.90). The MDC90 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 0.88) and by an inverse relationship between PST and external rotation (r 0.07).
The authors hypothesized that the PST measurement would have good interrater reliability based on the nature of the testing procedures. With regard to validity, it was hypothesized that a strong positive relationship would exist between PST and IR with little or no relationship between PST and ER.
Active measurements of IR and ER were used to establish validity since participants were healthy and without injury or neuromuscular impairments therefore soft tissue tightness was the most likely limiting factor for all measurements