Objectives: Evaluate the construct validity (structural validity and hypothesis-testing), reliability (test-retest reliability, measurement error and internal consistency) and minimal detectable change (MDC) of the 13-item TENDINopathy Severity assessment Achilles (TENDINS A). Methods: Participants with Achilles pain completed an online survey: demographics, TENDINS A, Foot and Ankle Outcome Score (FAOS) and Victorian Institute of Sport Assessment Achilles (VISA A). Exploratory factor analysis (EFA) assessed dimensionality. Confirmatory Factor Analysis (CFA) assessed structural validity [root-mean-squared error of approximation (RMSEA); Comparative Fit Index (CFI); Tucker-Lewis Index (TLI); Standardised Root Measure Square (SRMS)]. Correlations between TENDINS A and the FAOS/ VISA-A assessed hypothesis testing. Intraclass correlation (ICC) assessed test-retest reliability. Cronbachs alpha; assessed internal consistency. Standard error of the measurement (SEM) assessed measurement error. A distribution based approach assessed MDC. Results: Seventy nine participants (51% female) with a mean (SD) age=42.6 (13.0)years, height=175.0 (11.7)cm and body mass=82.0 (19.1)kg were included. EFA identified three meaningful factors, proposed to be pain, symptoms and function. The best model identified using CFA had adequate structural validity (CFI= 0.959, TLI= 0.947, RMSEA= 0.101, SRMS=0.068) excluded three items from the original TENDINS-A, included three factors (Pain, Symptoms, and Function). TENDINS A exhibited moderate positive correlation with FAOS (rho=0.598,p<0.001), moderate, negative correlation with VISA A (r=-0.639,p<0.001). Reliability of the TENDINS A is excellent (ICC=0.930; Cronbachs alpha;=0.808; SEM=6.54 units) and has an MDC of 12 units. Conclusions: Our evaluation of the revised 10-item TENDINS A has determined it has adequate validity and reliability. Thus, the TENDINS A can be recommended for immediate use, being the preferred tool over other PROMs to assess disability in Achilles tendinopathy.

The authors have declared no competing interest.

This study did not receive any funding

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This research was approved by the University of Notre Dame Australia Human Research Ethics Committee (Approval Number: 2022-175F)

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