Absolute and relative reliability of Pressure Pain Threshold (PPT) assessment in patients with nonspecific shoulder pain

This study investigates the intra- and interrater reliability of Pressure Pain Threshold assessments in patients with nonspecific shoulder pain, focusing on chronic and subacute stages. A sample of 26 adults was evaluated using a mechanical algometer across six anatomical points. Intrarater and interrater reliability were calculated using the intraclass correlation coefficient (ICC), standard error of measurement, and minimal detectable change (MDC). Results demonstrated almost perfect reliability for both intrarater (ICC range: 0.96-0.99) and interrater (ICC range: 0.92-0.99) assessments. Standard error of measurement and MDC values for intrarater reliability showed clinically acceptable error, except for the upper trapezius and mid-deltoid, where MDC value exceeded 25% of the grand mean, suggesting reduced precision between nonspecific shoulder pain stages. For interrater reliability, the adductor pollicis brevis, upper trapezius, and infraspinatus also showed less precision, with MDC values exceeding 25% of the grand mean, particularly in chronic patients. Despite these findings, no significant differences were observed between the subacute and chronic groups. While relative reliability was high, the findings highlight the need for caution in interpreting absolute reliability, especially for inter-rater assessments at specific muscle sites.