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

Abstract

Objective To evaluate the construct validity (structural validity and hypothesis testing), reliability (test–retest reliability, measurement error and internal consistency) and minimal important change (MIC) of the 13-item TENDINopathy Severity assessment–Achilles (TENDINS-A).

Methods Participants with Achilles pain completed an online survey including: 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 square error of approximation (RMSEA); Comparative Fit Index (CFI); Tucker-Lewis Index (TLI); standardised root measure square (SRMS)). Correlations between TENDINS-A and the FAOS or VISA-A assessed hypothesis testing. Intraclass correlation (ICC) assessed test–retest reliability. Cronbach’s alpha assessed internal consistency. SE of the measurement (SEM) assessed measurement error. A distribution-based approach assessed MIC.

Results 79 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 as pain, symptoms and function. The best model identified using CFA for TENDINS-A had structural validity (RMSEA=0.101, CFI=0.959, TLI=0.947, SRMS=0.068), which included three factors (pain, symptoms and function), but excluded three items from the original TENDINS-A. TENDINS-A exhibited moderate positive correlation with FAOS (r=0.598, p<0.001) and a moderate negative correlation with VISA-A (r=−0.639, p<0.001). Reliability of the TENDINS-A was excellent (ICC=0.930; Cronbach’s α=0.808; SEM=6.54 units), with an MIC of 12 units.

Conclusions Our evaluation of the revised 10-item TENDINS-A determined it has construct validity and excellent reliability, compared with the VISA-A and FAOS which lack content and construct validity. The TENDINS-A is recommended as the preferred patient-reported outcome measure to assess disability in people with Achilles tendinopathy.