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

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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This research was approved by the University of Notre Dame Australia Human Research Ethics Committee (Approval Number: 2022-175F) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors