TENDINopathy Severity assessment – Achilles (TENDINS-A): Evaluation of reliability and validity in accordance with COSMIN recommendations

ABSTRACT 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. Cronbach’s α 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; Cronbach’s α=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.