Pressure Pain Threshold in Subjects with Piriformis Syndrome: Test-Retest, Intra-, and Inter-Rater Reliability, and Minimal Detectible Changes

Abstract Objective This study aimed to assess the test-retest, intra-, and interrater reliability of using the pressure pain threshold (PPT) in healthy and affected piriformis muscles and to estimate its absolute reliability. As a secondary objective, the degree of tenderness of the affected piriformis muscles was compared with healthy piriformis muscles. Study Design This study used a comparative and reliability-based design. Setting Rehabilitation clinic. Participants Thirty patients with unilateral piriformis muscle syndrome (30 affected and 30 healthy piriformis muscles) were recruited, and the PPT of both the healthy and affected piriformis muscles was recorded using digital algometry. Measurements of PPT were done by two raters (rater 1 and 2), which have selected at random order. The rater 1 repeated the PPT measurements 24-72 hours after initial assessment. Interventions Not applicable. Main Outcome Measures PPT. Results Excellent intra-rater intra-class coefficient (ICC) values were observed for the PPT of the affected piriformis (ICC: 0.86–0.96) and the healthy piriformis (ICC: 0.88–0.96) in the same session. The PPT measurements using digital algometry showed good-to-excellent inter-rater reliability (ICC: 0.64–0.92) and test-retest reliability (ICC: 0.72–0.95) in both the healthy and affected piriformis muscles. The findings revealed a significant decrease in the PPT of the affected piriformis muscle in comparison to the healthy piriformis muscle (mean difference 12.76 [95% confidence interval [CI]:15.69–9.82], P Conclusion Digital algometry is a reliable tool for measuring piriformis PPT, regardless of the testing session and the rater. Patients with unilateral piriformis muscle syndrome have increased tenderness and decreased PPT in the affected piriformis muscle in comparison to the healthy piriformis muscle.